resistance in a wire experiment conclusion

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Lab Report Explained: Length and Electrical Resistance of a Wire

• Lab Report Explained: Length and…

INTRODUCTION AND BACKGROUND THEORY

When electrons travel through wires or other external circuits, they travel in a zigzag pattern that results in a collision between the electrons and the ions in the conductor, and this is known as resistance. The resistance of a wire causes difficulty for the flow of the electrical current of a wire to move and is typically measured in Ohms (Ω).

George Ohm discovered that the potential difference of a circuit corresponds to the current flowing throughout a circuit and that a circuit sometimes resists the flow of electricity. The said scientist hence came up with a rule for working out resistance, shown on the image on the side:

Resistance is an important factor to pay attention to because, one, an overly-high resistance can cause a wire to overheat due to the friction that is caused when the electrons move against the opposition of resistance, which is potentially dangerous as it could melt or even set fire. It is therefore important to take note of the resistance when dealing with wires to supply power to a device or so.

A real life application would be a toaster where the wires are sized to get hot enough to toast bread but not enough to melt.

Secondly, resistance can also be used a very useful tool that enables you to control certain things. An example from the real-life world would be LED lights that require a resistor to control the flow of the electrical current to prevent getting damaged by high electrical current. Another example would be the volume control on a radio where a resistor is used to portion out the signal, which allows you to control the volume level.

It is clear now that resistance is an important attribute that has been applied to many forms of technology to perform a useful function, and this experiment aims to see how we can control it. The resistance of a wire varies according to the four factors of the wire; are temperature, material, diameter/thickness, and length of the wire.

This experiment will be focusing specifically on that last factor – length – and investigate just how much of a role a length of a wire would have on its electrical resistance by using a range of wire lengths to test with.

RESEARCH QUESTION

How does changing the length of a nichrome wire with a diameter of 0.315 mm – cut into measurements of 10cm, 20cm, 30cm, 40cm and 50cm — affect the electrical resistance generated within the nichrome wires that can be captured by an ohmmeter while keeping the temperature and the location of the experiment controlled?

If the length of nichrome wire is increased by an increment of 10cm starting from 10cm in length, then the graph measuring the electrical resistance of the wires will observe a positive slope with the mathematical function of y = mx that displays the increasing amount of resistance generated.

REASON FOR HYPOTHESIS

Doubling a length of a wire is just like having two of the shorter wires in series. If one short wire has a resistance of 1 ohm, then 2 shorts wires would have a resistance of 2 ohms when connected in series.

A longer wire also means that it would have more atoms, which means it will be more likely for moving electrons to collide with them; hence, higher resistance. For instance, a 10cm wire has 5 atoms, a 20cm wire has 10 atoms. If say 5 electrons try to pass through those two wires, the chances of them bumping into atoms are higher in the 20cm wire than the 10cm one. Therefore, the longer the wire, the higher the resistance.

Source: “Resistance” Physics Classroom. The Physics Classroom, n.d. Web. May 8. 2018. [http://www.physicsclassroom.com/class/circuits/Lesson-3/Resistance]

MATERIAL AND APPARATUS

EXPERIMENT DESIGN SETUP WITH CLEAR LABELS

• Put on safety goggles, lab coats, gloves and masks for safety.
• Handle all materials carefully.
• Have a clear and clear working space for the experiment.
• Do not consume any of the materials used, and keep them away from the eyes.
• Complete all trials in the same area/room, at the same time of the day, using the same materials.
• Clean up the lab area after the experiment.
• Wash all materials thoroughly with warm water and soap after the experiment.

EXPERIMENT METHOD/PROCEDURE

• Gather materials and set up the circuit as shown in the experiment diagram above.
• Set the multimeter into ohmmeter, and connect the red probe to the output that says COM and the black probe to the output that has the mAVΩ label.
• Get 150cm of nichrome wire and scrap or rub it with sandpaper in order to make it conductive.
• Cut the wire with scissors into 5 separate wires with measurements of 10, 20, 30, 40 and 50cm.
• Measure each wire by putting the points of both probes to the edges of the wires, and measure them four times/trials each.
• Record the resistance reading from the multimeter of each of the 5 wires.

Recorded Resistance for 5 Different Lengths of Nichrome Wire

SAMPLE CALCULATION OF PROCESSED DATA

Average data no. 3: (6.50+7.00+6.50+7.90) ÷ 4 = 6.98 Average uncertainty data of no. 3: (7.90-6.50) ÷ 2 = 0.70

GRAPH (based on average data)

CONCLUSION & EVALUATION

The graph shows an increasing linear trend-line with the mathematical function of Y = 0.132X + 2.3, which displays a positive correlation as seen in the line that goes above and to the right, which indicates positive values, as well as the gradient that displays a positive value. The graph also has an identified slope or gradient of 0.132.

This unit for this gradient is ohm/cm, and the gradient represents the rate of the overall increase in the dependent variable as the independent variable progresses. The slope reveals that when the length of a wire is increased, the resistance would go up by an approximate measurement of 1.25 Ω, which could be proven by the calculation of the graph where all the average was calculated from the average increments of each wire — (0.7+0.78+2.42+1.1)÷4=1.25.

Another aspect from the mathematical function that can be identified is the Y intercept which was 2.3, and it represents the average resistance (dv) of the first data of the independent variable, which was 3.48 Ω.

The data for the length of wires (independent variable) was 10cm to 50cm with an increment of 10cm between each wire, while the resistance (dependent variable) seemed to display the lowest data of 3.48 Ω and the highest data of 8.48 Ω, which seems to fit well with modeled best fit line graph, which is visibly supported by the coefficient determination (R2) which states that the best-fit line fits the scattered data by 94.98%

The data does not perfectly fit the modeled best fit line as errors did occur along with the experiment, as displayed by the rather large error bars over the data. The maximum error bar that can be identified there is the 4th independent variable, which was the 40cm wire, and the minimum error bar was located in the 1st data, which was the 10cm wire.

Two data of the largest errors went way above the predicted line, which from it we can infer that the collected data is considered to have an inconsistent precision. When coming to measure those two data, the data gained from each trial were very inconsistent, which was presumably caused by the inconsistent rubbing with sandpaper, which will be further elaborated in the suggestions for improvements.

The pattern on the graph supports the hypothesis of the experiment which predicted that if the length of the wire increased, the resistance measured would increase as well, the graph will observe a positive gradient with the mathematical function of y = mx + c which is supposed to display the increasing amount of resistance.

This was proven and supported by the trend-line in the graph which basically shows a positive correlation in the increase in resistance at the same rate as the independent variable increases, which is just as the hypothesis predicted. The graph also manifested a positive mathematical function of y = 0.132x + 2.3 with a positive gradient (0.132x) as well.

There is, however, a scientific explanation behind all this. It has been a known fact that the length of a wire is one of the four factors that have a role in the resistance of the wire, and this experiment has simply confirmed it.

The logical explanation would be that a longer wire also means that it would have more atoms, which means it will be more likely for moving electrons to collide with them; hence, higher resistance. For instance, a 10cm wire has 5 atoms, a 20cm wire has 10 atoms. If say 5 electrons try to pass through those two wires, the chances of them bumping into atoms are higher in the 20cm wire than the 10cm one. Therefore, the longer the wire, the higher the resistance.

In conclusion, the experiment was a successful investigation that successfully answers the research question of how basically changing the length of a wire (especially a nichrome wire with a diameter of 0.315 cut into measurements of 10cm, 20cm, 30cm, 40cm and 50cm) could affect the electrical resistance generated within the wires.

The investigation has concluded that there is a clear relationship between the length and the resistance of a wire and that the former does in fact affect the latter.

EVALUATION AND SUGGESTIONS

BIBLIOGRAPHY

• “Potential Difference” BBC – GCSE Bitesize. BBC, Sep 15. 2006. Web. May 8. 2018. [http:// bbc.co.uk/schools/gcsebitesize/design/electronics/calculationsrev1.shtml]
• “Resistance” Physics Classroom. The Physics Classroom, n.d. Web. May 8. 2018. [http:// physicsclassroom.com/class/circuits/Lesson-3/Resistance]
• “Resistance and Resistivity” N.p., n.d. Web. May 8. 2018. [http://resources.schoolscience.co.uk/CDA/16plus/copelech2pg1.html]
• “Resistance: Chapter 1 – Basic Concepts of Electricity” All About Circuits. EETech Media, LLC, n.d. Web. May 8. 2018. [https://www.allaboutcircuits.com/textbook/direct-current/chpt-1/resistance/]

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excellent work. thank you ever so much.

Glowing regards, Shan

Data analysis?

indeed a great help

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GCSE Physics Required Practical: Investigating Resistance

• 1.1 Meaning
• 1.2.1 Variables
• 1.2.2 Method
• 1.2.3 Improving Accuracy
• 1.2.4 Improving Precision
• 1.3.1 Variables
• 1.3.2 Method
• 1.3.3 Improving Accuracy
• 1.3.4 Improving Precision
• 1.4.1 Variables
• 1.4.2 Method
• 1.4.3 Improving Accuracy
• 1.4.4 Improving Precision
• 1.5.1 Variables
• 1.5.2 Method
• 1.5.3 Improving Accuracy
• 1.5.4 Improving Precision

Key Stage 4

Investigate the factors affecting the resistance in a circuit .

Experiment 1a: Resistance and Length of a Wire

• Place the clips for the voltmeter at 5cm apart on the wire .
• Close the switch and read and record the current from the ammeter .
• Read and record the potential difference on the voltmeter .
• Use the equation \(V=IR\) to calculate the resistance of this length of wire .
• Repeat steps 3 and 4 increasing the distance between the clips by an interval of 5cm a further 5 times.
• Plot a scatter graph with the length of wire on the x-axis and the resistance on the y-axis . The gradient of line of best fit will show the relationship between the length of the wire and its resistance .

Improving Accuracy

Improving precision, experiment 1b: resistance and length of a wire.

• Place the clips for the circuit at 10cm apart on the wire .
• Close the switch .
• Read and record the potential difference on the voltmeter and the current from the ammeter .
• Repeat steps 4 and 5 increasing the distance between the clips by an interval of 10cm a further 5 times.

Experiment 2: Resistors in Series

• Connect a power supply and an ammeter in series with a resistor .
• Connect a voltmeter in parallel across the single resistor .
• Read and record the current from the ammeter and the potential difference from the voltmeter .
• Use the equation \(V=IR\) to calculate the resistance .
• Add an identical resistor in series and connect the voltmeter in parallel across both resistors .
• Repeat steps 3-5 for as many resistors as is available.

Experiment 2: Resistors in Parallel

• Add an identical resistor in parallel and connect the voltmeter in parallel across both resistors .

Collection of Physics Experiments

Dependence of wire resistance on its parameters, experiment number : 1763, goal of experiment.

This experiment verifies the dependence of wire resistance on its parameters (length, cross section) and conductor material. This experiment also involves a problem task.

Resistance of a conductor depends on the length, cross section and material of the conductor:

where ρ  is the electrical resistivity of the conductor, l  is its length and S  its cross section.

Electrical resistivity (also known as just resistivity) of a conductor made from a particular material can be found in The Handbook of Chemistry and Physics. Among the best conductors belong e.g. silver, copper, gold, etc. Bad conductors are e.g. Kanthal, constantan, carbon and others. The unit of electrical resistivity is derived from the equation (1) above after determining ρ :

Wires made from a material with a large resistivity are called resistance wires. Their resistivity varies from about 0.42·10 -6  Ω·m (nickeline) to e.g 1.4·10 -6  Ω·m (Kanthal).

Note: Equation (1) applies accurately to the wire with cylindrical shape, in which the current flows in the direction of its axis, but this is usually met with a normal wire.

• resistance wire
• ruler at least 1 meter long
• circuit connecting wires, crocodile clips
• scissors and sellotape if necessary

Use the ohmmeter to measure the resistance of the wire step by step by 10 cm. Make sure that the wire is properly attached to the ruler by crocodile clips.

Plot the measured values in a graph of resistance vs. length.

Measure the diameter of the wire and according to the relation (2) determine the electrical resistivity of the wire. Compare the resulting value with the value stated in The Handbook of Chemistry and Physics.

Sample result

This measurement was performed with a Kanthal wire 0.9 meter long with a diameter of 0.7×0.1 mm (the cross section is oblong, not circular). The measured values are listed in the table below.

If we plot the measured resistance values in a graph, the gradient of fitted line is the resistance of one meter of the wire.

The resistance of Kanthal wire one meter long is about 22.8 Ω.

If we substitute the measured values into the relationship for electrical resistivity of the wire (2) we obtain:

For comparison, the table value of resistivity of Kanthal is 1.4 μΩ·m.

The difference between the measured and the table value is given mainly by the contact resistance between the clips and the wire.

Technical notes

When conducting this experiment, you need to take into account the transition resistance between the crocodile clips and the wire – pay attention to the correct fixation of the clips; if needed, you can clean the oxidized ends of the wire with a sand paper.

It is necessary to conduct this experiment with a resistance wire, since the electrical resistivity of a copper wire is too small.

Problem task – cutting wire in half

What is the resistance of the wire, if we cut it in half and measure the resistance of both halves as shown in Figure 3.

Result of problem task – cutting wire in half

The solution is obvious from the equation (1) – the wire cut in half is two times shorter and has twice the cross section, its resistance will therefore be a quarter of the resistance of the whole wire. In our case the resistance is 5.6 Ω.

Link to a related problem

To solve a similar problem, see Electrical Resistances of Conductors of Different Lengths .

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Resistance of a Wire

14 Mar 2022

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For this experiment we must first explain two concepts, electrical resistance of materials and heating of materials by electrical energy:

Resistance is an electrical quantity that measures how the device or material reduces the electric current flow through it.  If we make an analogy to water flow in pipes, the resistance is bigger when the pipe is thinner, so the water flow is decreased. This is why copper is used in wiring in houses as opposed to other materials. Copper has a very low resistance and as such does not reduce the electric current flow very much. 

Some materials produce a great amount of heat when a current is passed through them. This can be seen in the case of light bulbs. When a current flows through the light bulb the filament heats up to a great temperature and then produces light. If you feel a lightbulb after it has been on for a while you can feel the heat produced. However more and more bulbs are no longer filament bulbs and are becoming LED bulbs which do not produced heat. Another example are fuses. Fuses are thin wires which, if the current gets too high, produces too much heat and melts the wire, burning aout the fuse and stopping the flow of electricity. 

Another example of a wire producing heat is in a calorimeter.  A calorimeter is a metal cylinder which is covered in an insulating material inside another cylinder. The lid if the calorimeter often has a coil of wire connected two two terminals on the outside of the lid. This coil goes down into the cylinder into a liquid, usually water. When current is passed through the coil of wire, the wire heats rapidly and that heat radiates out into the water heating it and the metal cylinder. The temperture of the water is measured using a digital thermometer.

The specific heat capacity of the system (Q) can be calculated by using: Q = (Cc * Mc + Cw * Mw )ΔT where Cc is the specific heat capacity of the inside cylinder, in this case aluminium,  Mc is the mass of the inside cylinder, Cw is the specific heat capacity of water and Mw is the mass of the water used. 

If the current remains steady over a time t, the rate at which electrical energy is converted to thermal energy in the coil (the power generated ) is given by P = Q/t where P is power and t is time.

The resistance of a section of an electric circuit is defined as R = P/I^2, where P is the thermal power generated in that section and I is the current through the wire. 

Putting all this together R = Q/(I^2 * t), the resitance of the wire can be calculated by

• first calculating the specific heat capacity of the system (Q) as described above
• Measuring the current going through the wire using an ammeter as seen in the diagram above (I)
• Measuring the total time the power is on (t)

You can try this lab out yourself with theis simulation / online lab:  Electrical Determination of Specific Heat Lab

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Verification of Ohm’s Law experiment with data and graph

In the previous article, we discussed Ohm’s Law of current electricity. In this article, we’re going to perform an experiment for the verification of Ohm’s law. This practical verification of Ohm’s law is very important for the students of grades 10 and 12. This is a lab-based experiment to verify Ohm’s law or Ohm’s law practical.

Aim of the Experiment

Theory of the ohm’s law experiment.

From Ohm’s law , we know that the relation between electric current and potential difference is V = IR

or, \color{Blue}R=\frac{V}{I} ………….. (1)

or, resistivity, \color{Blue}\rho = \frac{RA}{L} ………. (2)

Where A is the cross-section area of the wire. A = πr 2 where r is the radius of the wire. L is the length of the wire.

Apparatus Used

The apparatus used for this experiment –

Circuit Diagram

Here, R is the resistance of the wire, A is the ammeter, V is the Voltmeter, Rh is the rheostat and K is the key. The arrow sign indicates the direction of the current flow in the circuit .

Formula used for the Ohm’s law lab experiment

\color{Blue}R = \frac{V}{I} ………….. (1) and \color{Blue}\rho = \frac{RA}{L} ………. (2)

Experimental data

The least count of Voltmeter = Smallest division of voltmeter = 0.05 Volt

We also need to plot I-V graph to confirm the experimental value of R.

Current versus Voltage graph (Ohm’s Law graph)

If we plot the Current as a function of voltage with the help of the above data then we will get a straight line passing through the origin.

Calculations

Calculation of resistance from the graph.

The inverse of the I-V graph gives the resistance of the wire. Now, from the graph, change in current, ∆I = AB = 0.5 amp corresponding change in voltage, ∆V = BC = 0.5 volt Thus, the Resistance from the graph, R = ∆V/∆I = 0.5/0.5 = 1.00 ohm

Calculation of resistivity of the wire

Length of the wire is, L = 50 cm = 0.5 m Radius of the wire. r = 0.25 mm = 0.25 × 10 -3 m So, the cross-section area of the wire, A = πr 2 = 3.14 × (0.25×10 -3 ) 2 = 0.196 × 10 -6 m 2 Thus from the equation-2 we get the resistivity of the material of the wire is, \rho = (1 × 0.196 ×10 -6 )/0.5 or, \rho = 0.392 × 10 -6 = 3.92 ×10 -7 ohm.m Thus the resistivity of the material of the wire is 3.92 ×10 -7 ohm.m

Final result

The resistance of the wire from the Current-Voltage graph is, R = 1.00 ohm The calculated value of the resistance of the wire is, R = 1.02 ohm. Resistivity of the material of the wire is 3.92 ×10 -7 ohm.m

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• Misconceptions
• Classroom Physics

Investigating the resistance of wires

Class practical

A simple investigation of the factors affecting the resistance of a wire.

Apparatus and Materials

For each student group

• Cells, 1.5 V , with holders, 2
• Crocodile clips, 2
• Ammeter (0 - 1 amp), DC
• Leads, 4 mm, 5
• Wire available for class use (see technical notes)
• Power supply, 0 to 12 V , DC (OPTIONAL)
• Metre rule (OPTIONAL)
• Insulating tape (OPTIONAL)
• Digital and analogue ammeters, 0-1 A (OPTIONAL)
• Digital and analogue voltmeters, 0- 12 V (OPTIONAL)
• Micrometer (OPTIONAL)

Health & Safety and Technical Notes

Modern dry cell construction uses a steel can connected to the positive (raised) contact. The negative connection is the centre of the base with an annular ring of insulator between it and the can. Some cell holders have clips which can bridge the insulator causing a short circuit . This discharges the cell rapidly and can make it explode. The risk is reduced by using low power , zinc chloride cells not high power , alkaline manganese ones.

When using a power supply, high currents will cause the safety cut-out on the power packs to automatically switch it off. If short lengths of wire are used with relatively high currents and voltages, then significant electrical heating may also occur. Students should be encouraged to adjust the voltage to keep currents small with every set of readings. At each stage they can connect the circuit, take readings quickly and then disconnect the power supply.

If you use a mains power supply, use one that is designed to limit the output current to about 1 amp, and preferably with a current overload indicator.

Read our standard health & safety guidance

The following apparatus should be available for class use:

• Selection of reels of Eureka wire (also known as Constantan or Contra) of different gauges, e.g. 0.71 mm (22 SWG), 0.46 mm (26 SWG), 0.32 mm (30 SWG) and 0.24 mm (34 SWG).
• Selection of reels of different wires (e.g. copper, Eureka, iron) of same gauge (e.g. 34 SWG).

• Connect up a series circuit of two cells, and the ammeter, with a 30 cm length of one of the wires closing a gap between two crocodile clips. Note the reading on the ammeter.
• Replace the specimen of wire with another of the same length but different gauge or material.
• Investigate how the current depends on the thickness of the wire, its length and the material from which it is made.

Teaching Notes

• Use fine gauge wires. If too thick a wire is used, the results may be affected by warming of the wires.
• If coils of copper and Eureka wires of the same gauge can be prepared so that they have equal resistances, the effect is very striking. However, this would then lose its value as an open investigation.
• Students should come to understand that the resistance of a wire depends on its length, its cross sectional area, and the material out of which it is made. With some students you could go further and introduce the concept of resistivity ρ, through the relationship R = ρ l / A where R = resistance, ρ = resistivity, l = length and A = cross-sectional area.
• This may also be an opportunity for a large scale demonstration of the effect by the teacher. But note: if the current is too large, the voltage of the cells will fall due to their internal resistance. For this reason, it is important to keep the current very low - copper wire is effectively a short.
• How Science Works extension: This experiment can be used as a more open-ended investigation. Students can select the variables, the ranges of results and the equipment used. The amount of guidance will depend greatly upon the teaching group. Investigating the effect of length on resistance is common but some students may wish to investigate the effect of the thickness of wire. In either case, different wires should be made of the same material. Students may need to know the conversion between SWG (standard wire gauge) and wire diameter/radius.
• Students will find it easier to measure at a prescribed length if they tape the wire to a metre rule with insulating tape and make connections with flying leads rather than crocodile clips.

This experiment was safety-checked in August 2007

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Determination of the specific resistance of a wire using a metre bridge

Introduction

Experimental Data

Reading of the balance point

Calculation

Percentage of error

• The wire used may not be uniform area of cross-section. So, it is essential to choose a suitable wire.
• Effect of end resistance due to copper strips, connecting screws, may affect the measurement. So, it is essential for taking proper measurement.
• All the connections and plugs must be tight.
• Jockey must be moved gently over the metre bridge wire.
• Null point may be far away from the middle.
• It is essential to take determine the diameter of the wire accurately.
• E.M.F of the cell must check before starting the experiment. The E.M.F of cell must be constant.
• The length measurements l and l΄ may have error if the metre bridge wire taut and along the scale in the metre bridge. So, it must be ensure to taut the metre bridge along the scale.
• The resistance of end pieces/metal strips may not be negligible. The error introduced by it can be reduced by interchanging the known and unknown resistance in gaps.[6]
• The percentage of error increases if the resistance box or other materials may not be clean. So, all the materials must be clean.
• The reading of screw gauge might be accurate.

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Resistance and Wires

21st Century Additional Science

Written Science Experiment - Resistance and Wires

How is the resistance of nickel-chrome wire affected by its length and diameter?

Introduction

This investigation determines how changing the length of Nickel-Chrome (nichrome) wires, when passing an electrical current through them, affects their resistance. It also determines how resistance is affected by a change in the diameter of the wire used. Resistance is "the property of failing to conduct electrical or thermal energy".

Resistance is a force which opposes the flow of an electric current around a circuit so that more energy is required to push the charged particles around the circuit. The circuit itself can resist the flow of particles if the wires are either very thin or very long, e.g. the filament across an electric light bulb.

Resistance is measured in ohms. A resistor has the resistance of one ohm if a voltage of one volt is required to push a current of one amp through it.

George Ohm discovered that the emf (electromagnetic force) of a circuit is directly proportional to the current flowing through the circuit. This means that if you triple one, you triple the other. He also discovered that a circuit sometimes resisted the flow of electricity. He called this, resistance. He then came up with a rule for working out the resistance of a circuit:

V÷I = R, V= I×R and R=V÷I

V –Voltage (volts) I – current (amps) R – resistance (ohms)

In conducting this experiment I examined the resistance of Nickel-chrome wire. I am investigating 2 variables that affect the resistance of the wire in this investigation. They are the diameter of the wire and the length of the wire. This experiment queries the relationship between voltage, amps and resistance flowing through nickel-chrome wire with various properties. The results of both experiments will be compared and conclusions drawn about how the resistance changes, according to the length of the wire and the diameter of the wire. A description of comparisons between the trends in the results of each experiment will be made and the ways in which the resistance of nickel-chrome wire changes as its length and diameter are adjusted, will also be evaluated.

Before the experiment had begun, I predicted that concerning the first experiment, the longer wire the more the resistance and in the second experiment the thinner the wire the higher the resistance. This is because the electrons of a current flowing through short wire have less distance to travel and therefore have fewer collisions causing less resistance than they would get traveling further. Collisions cause a loss of energy. In a thick wire they have more space to move around and are therefore less likely to collide with each other. (The more the electrons collide together, the higher the resistance.)

During each test in this investigation there were several factors that I needed to control or keep constant, to ensure that my results would be as reliable as possible. These included temperature of the wire and the voltage and current in the circuit. These are dependent upon the voltage input. By ensuring that the voltage in each experiment is low enough that it does not heat up the wire and yet high enough that I can record clear readings, the test will be as fair and useful as it could be. The temperature contributes to the amount of resistance in the circuit. Therefore, I will have to keep it constant, to enable me to be sure that my results can be trusted. To reduce the chance that the wire is hot when tested, I made sure that I turned off all power in the circuit between each recording. This meant that the wire had less time to heat up. By including an ammeter in series with my circuit, I will be able to record the amount of current flowing through it and check that it stays constant before each test. This will also enable me to calculate resistance. There was no change in current during the first experiment however in the second each diameter caused a change in current. This change was taken into consideration when I came to calculate resistance. By using the same voltage input, from the power pack each time in my investigation, I was also able to ensure that the voltage in the circuit was the same each time. I also made sure that the external temperature was approximately constant throughout my investigation.

It was necessary not allow the wires to build up heat. This is because in metal conductors, electrical current flows due to the electrons being transferred between atoms. As electrons move through a metal conductor, some collide with atoms or other electrons. ( See diagrams on figure 1 on next page) . These collisions cause resistance which generates heat. Heating the wire causes atoms in the wire to vibrate more, which in turn makes it more difficult for the electrons to flow, increasing resistance. This increase in resistance changes the recordings of data by increasing potential difference and therefore increasing resistance. This would have make the test unfair and caused the results to be inaccurate and unreliable. This factor had to be controlled during each area of investigation.

I took special care in deciding what voltage to use for each experiment because a large amount of voltage can cause the wire to heat up, causing resistance, however a voltage that is too low, can cause inaccurate or unclear readings.

The variable in the first experiment was the length, of test wire that is used in the circuit. The variable in the second part of the investigation was the diameter of 10cm of nickel-chrome wire. I chose these variables for this investigation because they can be manipulated in various ways as shown in the experiment. They are of reasonable complexity, with many variations to the experiment. The data once analyzed reveals many patterns and the equipment needed for this test was reasonably easy to get.

Experiment 1

The purpose of experiment 1 was to examine how resistance is affected by a change in length of wire.

For this experiment, a factor that could affect the resistance of the wire, and which is not a variable in this experiment is the heat of the wire. This factor is a major reason for resistance in hot wires and is a factor which I am not intending to record the effects of, in this investigation. As described above, heat in a wire causes more resistance than if there was no heat. Therefore this factor will need to be controlled during the experiment ( see figure 1 on page 3b, in the introduction section) .This can be done by making the voltage as low as possible, without it being so low that a clear reading cannot be recorded. Resistance in the copper wire need not be an issue, because copper is a very good conductor of electricity and transfers the electrons most efficiently.

In the first experiment, I measured each recording of the test wire in exactly the same way to ensure that the test was fair. I measured the potential difference of the length of test wire. In order to do this, the conducting rod was placed at points along the wire. The conducting rod was fixed to the circuit at one end, and when connected to the test wire, created a complete circuit where the current could flow through the test wire. The voltmeter displays the potential difference of the test wire. The points were recorded in stages of 10cm. I took 10 readings from 10cm up to 100cm (1m). This means that when the rod is placed only 10cm away from the beginning of the wire, the current only flows through that 10cm of the test wire. As the rod is moved along the test wire, more of the test wire is used by the circuit. Therefore, as more test wire is being used, the potential difference of the wire changes.

I conducted the first experiment, to find out how changing the length of nickel-chrome wire affected its resistance. To enable me to conduct this second experiment, I used the following equipment:

• Power pack - as a supply of power
• 5 wires – to connect up the circuit and measure voltage
• An ammeter – to measure current
• A voltmeter – to measure voltage
• The 100cm length of nichrome wire attached to a ruler – to enable the length of wire to be calculated accurately, increasing reliability and accuracy.

The circuit diagram below shows the circuit used in the experiment:

CIRCUIT DIAGRAM 1

As shown, the ammeter was in series wire the circuit. This was necessary to give an accurate reading of current. The voltmeter was used in parallel because I was measuring potential difference. The voltmeter measured the potential difference of the area of which it was in parallel with.

Due to the fact that this experiment involves a long wire, I chose to use 10v DC in the circuit. This will ensure that a clear range of potential difference can be recorded from beginning to end of the test wire. Heat in the test wire at this voltage should not have been a problem, providing the power is turned off in between each recording to ensure that there is no gradual build up of heat in the test wire. 10v would ensure that potential difference could be accurately recorded right up to the end of the test wire. I did however make sure that the wire did not heat up during the experiment by feeling for heat. I also made sure that I turned off the power between each experiment to prevent any gradual increase in heat due to resistance. I only turned on the power for a brief moment to give me enough time to take the readings.

I had an instant when I had set up the investigation wrong in this experiment and the circuit was not correct. This caused a large amount of heat build up in the wire so much that it causes the wire to burn through the ruler which it was attached to and burned through itself causing it to break. This burning happed when the conducting rod was near the end of the wire. I later concluded that the reason for this was partly due to the fact that I was using such a high voltage, but mainly because all of the energy was being transferred into heat due to the resistance in the wire over a short amount of space. This is because there was only a short amount of nichrome wire that was being used to conduct the voltage. This caused over heating due to the resistance. As heat increased, the rate that the wire was heating up increased because the extra heat was causing more resistance, causing more heat do be developed at a faster rate.

To ensure that the results are as accurately, each reading will be taken 3 separate times and a mean will be calculated from them. This will improve the accuracy and reliability of the recorded data.

By recording the current (using the ammeter) and potential difference (using the voltmeter), change in resistance can be calculated. This data will be placed on a graph and analyzed.

I will use various calculations to find the resistance of the wire (in Ohms), as different lengths of nickel-chrome are used. These include: V÷I = R which can be manipulated into V= I×R. The drawing (figure 1) shows the circuit diagram.

In my prediction I stated my opinion that resistance should increase as the length of the wire increases. After conducting the test, I found that my prediction was indeed correct and there was a clear trend which showed an increase in resistance at a steady rate. The graph shows this trend.

Analysis of Experiment 1

This is a preview of the whole essay.

This table shows the potential difference of various lengths of nichrome wire when included in the 10v circuit:

To show how the resistance was calculated, here is an example of the process of calculating resistance. This calculation was for the first recording of the mean of 10cm of wire. I used the formula, V÷I=R. (1.00+0.97+0.93) ÷ 3 = 0.97 (mean). 0.97(voltage) ÷ 0.56 (amps) = 1.7(ohms).

These tests were done using a 1m length of wire with a diameter of 34mm. I chose to use 10v of voltage because it gave the clearer results than a lower voltage because the numbers where higher. I made certain that this voltage did not heat up the wire. I felt the wire and found no heating effect.  Therefore there was little additional resistance caused by the temperature of the wire.

I originally chose to record the results for this experiment using 3 decimal places (3d.p.) however due to an error in the recording of current in this experiment; the only data available is resistance to 1d.p. The error in this experiment was a small and single mistake but one which had a huge affect on the results. When I was recording the current for this experiment, it is most likely that I either misread the ammeter when recording current (56amps instead of 0.56amps), or it could have been a typing error. I may have entered 56amps into the table instead of 0.56amps. I chose to use the results to 3d.p. because I realized the mistake, the results for resistances were all in decimal places, and therefore the significant figures were all below the decimal point. Therefore by having 3d.p, plotting an accurate graph is easier and the results are clearer to analyze and evaluate.

These results support the claim that the results are very accurate. There is also a definite trend or pattern which the results follow. This also supports the fact that the data is accurate because it there are no stray results and each reading fits nicely into a pattern when drawn on the graph.

See Graph on the next page

The graph shows the relationship between the length of nichrome wire, and its resistance. Length (cm) is plotted on the 'X' axis as the independent variable and on the 'Y' axis is the resistance (ohms) being the dependent variable.

The results from the graph indicate a steady increase in resistance as the length of wire increases, shows by the positive correlation of the graph. The relationship between the length and resistance of the wires is shown by the graph to be a proportional relationship. The resistance of the wire is proportional to the length of the wire. The graph clearly shows that the longer the wire, the higher the resistance. As the wire gets longer, the resistance is increased.

E.g. At 20cm there is a mean of 3.3ohms of resistance. At 80cm of wire, the mean resistance is 12.4ohms.

This is evidence to suggest that the longer a piece of wire, the more resistance it has. This increase of resistance is at a steady and constant rate of increase. This is shows because the ‘line of best fit’, goes through the center of each mean recording. This is also shown as the increase of resistance every 10cm is the same. The graph indicates an increase of 1.5ohms every 10cm. So for every 10cm of nickel-chrome wire with a diameter of 34mm, 1.5ohms of resistance is added on.

The range bars, shown on the graph show how accurate the results are. A smaller range bar indicates a very high degree of accuracy; however a larger range bar indicates a low degree of accuracy. As shown on the key, on the graph, the highest line on the range bar represents the value of the highest recording taken from the experiment, and the lower line represents the lowest value. The cross in between the two lines represents the mean result. This is the most accurate result, calculated by dividing the sum of each recording by the number of recordings. The graph is indicated additionally accurate due to the fact that the ‘line of best fit’, goes through each mean recording. In this test there are no anomalies, shown because each recording fits into the general trend. In other words there is a narrow channel in the spread of data, shown in the range bars and ‘line of best fit’.

The graph shows a trend in the results that goes up, as length is increased. This shows that the relationship between length of the nichrome with and resistance is that the more length that the wire has, the more resistance the wire has.

This graph could be described using the equation y=nx. For example if n was 3 and x=2 then y would equal 6. This can be found by dividing the mean resistance by the length of wire. So for the first test for 10cm, 10÷1.7=5.88(2d.p.). So in this case y=nx, if n=5.88(2d.p.) and x=1.7. For the second result for 20cm, 20÷3.3=6.06(2d.p.). So for the second result, y=nx, if n=6.06(2d.p) and x=3.3. This graph showed what ‘n’ is for each length of wire.

This graph tells us what ‘n’ would be to enable the formula y=nx, to work for each result. This is useful to us in that it enables us to see in detail, the accuracy of our results. This is because the results appear to be in exact proportion between their length and resistance. This calculation tells us that that is in fact not completely true for this experiment. As shown in the table, the results do tend to increase. This should not be the case if the two variables are in direct proportion to each other. This increase in the value of ‘n’, can however be explained. My explanation for this is similar to the reason for the range bars increasing in size of scatter as length is increased. I assume that it is due to the fact that I conducted the tests chronologically from the shorter length of wires, to the longer lengths. Due to the fact that I used the same wire each time, the temperature could have increased marginally despite the fact that I momentarily turned the power off between each recording. This amount of time when the power pack was off, may not have been long enough. The heat could be building up in the test wire, causing an increase in resistance and shown on the diagrams on page 3b in the introduction section. If drawn on a graph, and if the results had been more accurate by me waiting for the wire to cool down for longer,  the results for ‘n’, in the equation y=nx, would have shown an exactly straight line because the relationship between length and resistance is directly and exactly proportional as calculated below.

I calculated the mean value of ‘n’ by using the values of ‘n’ for the various lengths. I calculated the value of the mean by adding up all the 10 values for ‘n’, and dividing that sum by the amount of results which was 10. This gave me 6.31. This mean is not however accurate due to the results not being completely accurate as mentioned above. A much more accurate way of calculating a value of ‘n’ that should would work in the equation y=nx would be to use the value of ‘n’ for the result taken first in chronological order because here there is no unfairness in the result caused by heat because the wire could not have been heated. This value is 5.88. Obviously this value is not 100% accurate, partly due the fact that the calculations of ‘n’ were only taken to 2d.p, but it is the most accurate reading of ‘n’ that I can conclude with. This value of ‘n’ can be used for any length due to the fact that the relationship between length (y) and resistance (x) is always directly proportional.

Therefore this value of ‘n’ can be used to calculate the resistance of any length of wire. For example if ‘n’ is always 5.88, then y=5.88×x. So 5.88×x will always give the length of wire that has that specific resistance. And y/5.88 will always give the amount of resistance that that length of wire has. This value of ‘n’ only is relevant to wires with the same diameter as that of which ‘n’ was calculated (34mm). For example, if I were to find the value of the resistance of a wire with a length of 250cm I would use the calculation 250/5.88. This would give me an answer of 42.5ohms. Or if I were to calculate the length of wire with a diameter of 34mm when the resistance was 5ohms, I would use the calculation 5.88×5. This would give me an answer of 29.4cm. This can be proved to be reasonably accurate when plotted on the graph. I have done this as shown on the graph. The reading given by the graph is 31cm, which considering the possibly inaccuracy of the value of ‘n’, is evident to support the reliability of the equation and the accuracy of the recorded results.

It is possible to calculate the amount of resistance 10cm of wire has by reading the graph to measure how much resistance increases every 10cm along the wire. To calculate the amount of resistance that 10cm of wire has, I simply read across the graph from the mean point of 10cm to the ‘y’ axis and found the resistance to be 1.8ohms. Then I did the same for the recording of 20cm, and found a measurement for 3.3ohms. To calculate the resistance change I deducted 1.8 from 3.3 which revealed a change in resistance of 1.5ohms. This is therefore shown to be the amount of resistance that 10cm of the wire has because the different in resistance between 10cm and 20cm (10cm difference in length) is 1.5ohms.

I calculated the resistance of 15cm of the wire, by reading the resistance in ohms when the length of wire is at 25cm. The graph shows how I read the recording. The graph showed that at 25cm, there was a resistance of 4.0ohms. By deducting the previous recording for 10cm of 1.8 from 4.0, 2.2ohms remains. ). 2.2ohms is therefore the amount of resistance that 15cm of wire has because the difference between 10cm and 25cm is 15cm. This method can be used to find the amount of resistance for any length of wire, providing it is nickel-chrome wire with a diameter of 0.34mm. This method will only be accurate with a wire with these properties because the wire used to record this data did have these properties. Any change in these properties would resistance to be different and therefore each length of wire would have a different resistance.

As briefly mentioned before, these results, on the whole are very accurate due to the fact that careful consideration was taken in planning to produce results with very small parameters, shown by the narrow range bars. Accuracy is also shown as each mean results is almost an exact fit into the ‘line of best fit’ of the graph.

Despite this accuracy, the results from higher lengths of wire are shown to have a wider parameter in the range bars. This indicates slight inaccuracy in the recordings. A possible reason for this could be that despite me turning off the equipment in between each recording, the wire could have heated up, and retained some of the heat from the previous recording. This theory fits the pattern because the range bars become wider as the length of wire is increased. Due to the fact that the shorter amount of wire was measured first, an increase in heat over time could have caused a gradual increase in resistance, which produced the increase in the size of the range bars. This is not a certain reason, however it is probable. Assuming that this idea is correct, the lower parameters would have been recorded first at a lower temperature, and the higher parameters of the range bars would have been recorded later on when the wire was hotter.

 If I were to conduct this experiment a second time, I would increase the amount of time that the power was turned off, to ensure a sufficient amount of time to allow the wire to fully cool down. This would mean that each range bar would be of a more similar size and they would not increase as length was increased.

As shown on the graph, the line of best fit if kept straight would not go through the point (0, 0) on the graph. It is assumed that the graph may go through this point; however this is not indicated by the graph. This could either be due to a recording error or a lack of detail in the recordings. The idea of a recording error can be tested by re-conducting the experiment. A much more likely explanation is that the measurements were not detailed enough to show a slight curve in the beginning of the ‘line of best fit’. Assuming that the results are in the correct positions, the remaining explanation would be that if the gaps between the independent variables were smaller, e.g. every 1cm, results could have revealed a slight curve in the trend of results. This would answer this question.

It is possible that as shown with the current data, the results, despite a lack of detail, do not appear to curve towards (0, 0), but instead continue to around (0, 0.004).This could be possible because at the instant that the length reaches the ‘Y’ axis, the resistance could drop to 0 ohms. This is surely the case because no wire, has no resistance, however the minutest amount of wire could begin at a certain amount of resistance, without following a proportional ‘line of best fit’ from (0, 0), at a rate of increase of 2.6ohms per 10cm. The presence of a small amount of wire could result in a disproportional amount of initial resistance.

In conclusion of this experiment, the results show that as the length of the nichrome wire is increased, the resistance of it increases. The amount of resistance caused by a certain length of wire being added on can be calculated by measuring the difference in resistance between two values of length with a difference of the amount of wire that is being measured for resistance. For example to find the resistance of 10cm of the 34mm nichrome wire the calculation would subtract the resistance of 20cm of wire with the resistance of 10cm to reveal the resistance of 10cm of wire. As shown above, this difference in resistance is 1.5ohms. Therefore it is clear that for every 10cm of wire added on with the same diameter, 1.5ohms of resistance will be added. These results support my initial prediction and so my prediction about the relationship between resistance and length was indeed correct.

There are, however some limitations to the conclusion due to the scatter in the range bars. The scatter or size of range bars increases quite a large amount as the length of wire is increased. This increase in the amount of scatter is not coincidence and there is no certain explanation for this. As explained above the simplest explanation is that between each recording, a fragment of heat had been built up in the wire, despite the precaution of turning off the power pack between each reading. No definite conclusion can be drawn from this due to the fact that the reason for this scatter is unsure. This limits the amount or detail of the conclusions that can be made, and therefore decreases the complexity of the investigation, however if I were to re-conduct this experiment, it would be possible to leave more time for the wire to cool down. If then, there was not an increase in the range of scatter, it would give sufficient evidence to support this previously described explanation and therefore a more confident conclusion could have been made and supported with accurate data.

To extend this part of the investigation further I could have drawn a graph that would have shown the results of the calculations of the n th term. This would have enabled me to analyze further, the reasons and causes for the slight increase in the value ‘n’ as length is increased. It would also have more graphically displayed the trend. I would have also been able to include the mean value of ‘n’ on the graph. I could have annotated the graph to explain in more detail how this equation works.

Experiment 2

In the second part of the investigation I am going to use several lengths of nickel-chrome wire with different diameters to find out any change in resistance between the different diameters of wire.

In this second experiment I chose to use only 2v DC of voltage because the test wire was that much shorter than in the first experiment.

To ensure that the results are as accurate as they can be, each reading will be taken 3 separate times and a mean will be calculated from them. The diameter of each wire will be calculated 3 times and a mean taken to ensure an accurate reading. This will improve the accuracy and reliability of the recorded data.

Preliminary Test

I have conducted a preliminary test, to ensure that the second part of my experiment will work and have clear results which show a definite trend. The width of the nickel-chrome wire will make a difference in the resistance of the wire because in a thin wire, there are a lot of electrons which have to travel in a proportionally small channel. This causes a lot of collision with other electrons. This collision causes friction, which produces heat. This heat energy which is produced causes resistance because electrical energy from the current is being transferred into heat energy. These facts are backed up with the data results from my preliminary test, shown below. Resistance was calculated using the formula V÷I = R.

As I was conducting this preliminary test I made absolute certain, that my results were accurate by ensuring that each length of wire was exactly the same length, and I reduced the voltage input from 12v DC down to 2v DC in order that the wires, particularly the thinner wire, did not heat up. This would have altered the resistance of the wire because the more heat energy that the wire has, the faster atoms move in the wire, and so the electrons in the current have more collisions. This causes friction, which produces heat ( see figure 1 on page 3b, in the introduction section) . Heat is produced using energy from the electrical current. This causes the overall resistance to increase because there is energy being taken from the electrical current. These results show that a thicker wire has a much smaller resistance than a thinner wire. This preliminary data supports my initial prediction which stated that thinner wire will have more resistance than thicker wire. I calculated the resistance of each wire using the formula, R=V÷I. R is resistance in Ohms, V is voltage or potential difference in Volts and 'I' is current, measured in amperes/amps. The higher that the number of Ohms is, the higher the resistance of the wire is. In conducting the preliminary test, I used the following instruments: power supply (set to 2V), 5 copper wires, 2 crocodile clips, an ammeter, a voltmeter, and the nickel-chrome wires both thick and thin.

• Collect apparatus: a voltmeter, an ammeter, 5x wires, 2 crocodile clips, 7 nichrome wires with different diameters and a power pack.
• Set apparatus up as shown:

DRAW DIAGRAM OF CIRCUIT 2

• Set the power pack on as low a voltage as possible, 2v. (So that the voltage doesn’t cause the wire to heat up.)
• Place the nichrome between the two crocodile clips to complete the circuit.
• Turn on the power pack and record the current from the ammeter and the voltage from the voltmeter.
• Turn off the power pack.
• Repeat this process for all the diameters of wires.
• Work out the resistance for all the results using Ohm's law. V = I*R
• Record the results on a graph.

My results are shown to be accurate because I conducted the test 3 times and calculated the mean to 2 decimal places. The results above are the mean values. I also conducted the short experiment using only 2v DC to ensure that neither of the wires began to heat up.

To increase the accuracy of the measurements taken of the diameter of each wire, I conducted an experiment whereby each wire was measured using a micrometer 3 times. A micrometer works by clamping the wire between the spindle face and anvil face. They are adjusted by rotating the ratchet. This moves the spindle and thimble down the sleeve. The sleeve has numbers on it which displays the wires diameter when tightened. The table of results from the measurement of the wires is shown below:

The mean was calculated in the way shown in the calculation: (Test 1 + Test 2 + Test 3) ÷ 3 = mean. So, (0.25 + 0.26 + 0.22) ÷ 3 = 0.24.

These results are clearly very accurate because each measurement for the same wire, are very close to each other, (each within 0.2mm). This is good evidence to support the accuracy of my results. I will use these results when analyzing the data. Due to the fact that these are accurate, any outliers in the graph will be due to an error in the readings or calculations of voltage, current or resistance.

I conducted the second experiment, whereby nickel-chrome wires of 7 different diameters were tested for resistance.

The set up of the circuit is very much similar to the first experiment. I used for this test, an ammeter, a voltmeter, lengths of copper wire, 2 crocodile clips, and a power pack in addition to the test wires. The power pack was adjusted to output only 2v DC. This was to prevent the wires from heating up which would cause additional resistance. The ammeter will be placed in series with the circuit and will record the current flowing through the circuit. The voltmeter will be put in parallel with the test wire using crocodile clips. Any recorded potential difference is in fact that of the test wire only and not of the copper wire since the voltmeter was in parallel, only to the test wire. See diagram above.

Analysis of Experiment 2

I initially planned to use a higher voltage of 10v for this experiment but this caused the wire to rapidly heat up making it impossible to take an accurate reading of the potential difference. The heat as mentioned above causes additional resistance. As I was experimenting before the investigation began I found that 10v did heat up the wire. There was only one outlier or anomaly in this experiment which was the recording of the current of the wire with a diameter of 0.88mm. This was recorded in set 1, as 2.85amps. This reading was 22mm different from the recording in set 2, whereas other recordings of wires with different diameters had been much closer to each other. This is not a major difference, however could have affected the overall pattern. In order to take appropriate action I therefore did not include these results when calculating the mean for this diameter, and therefore did not use the reading for voltage in set 1. I therefore calculated the mean by using only 2 results. This should not however have affected the accuracy of the mean, because the calculation of resistance of this diameter remains to fit in the trend line on the graph.

Here the graph shows the relationship between the diameter of 10cm of nichrome wire, and the resistance it has. Diameter is plotted on the 'X' axis and is the independent variable, however on the 'Y' axis is the resistance which is the dependent variable.

The results from this experiment are shown on the graph comparing diameter with resistance. The displaying of the results indicates that the thicker the wire is, the less resistance it produces. This assumption is based on the narrow range of results shown. As described above, these results are highly accurate. The range bars support this claim as they have a very small range. This shows that the range of data recorded for each diameter of wire is very close to each other and so the possibility that the results are inaccurate from this perspective is very unlikely.

As shown by the graph comparing diameter with resistance, the majority of change in resistance is between 0.24mm to 0.56mm. This means that between these narrow ranges a large percentage of the overall resistance change is lost. In contrast, the range of diameter from 0.9mm to 1.2mm has a much smaller drop in resistance. These figures indicate that when a nichrome wire has a diameter of 1.2mm or more, there is only a small change in resistance is the wire was to increase in diameter. These assumptions do only apply for nichrome wire when a voltage of 2v is passed through them. To expand this experiment, a similar test could be done, however with different ranges of voltage. This would enable me to analyze how the voltage changes resistance, in wires with various diameters

To manipulate this data it is possible to record how much resistance is loosed between different ranges of diameter. This can be done by measuring how much resistance is lost every time the diameter of the wire changes 0.1 of a millimeter. For reasons due to a lack of data, I can only being by recording from 0.3-0.4mm. This is because my results do not cover diameters of 0.2 and below and so this would not be accurate. As shown on the graph, I have drawn a trend line to fill in the gaps between the results to predict the resistance of more detailed diameters. In other word the trend line shows me what the resistance of the diameters of wire which were not recorded was most likely to be. This is a reasonably accurate technique due to the fact that my results are accurate, shown by the range bars.

This trend line enables me to read the resistance of the wires of a diameter with a whole decimal number, e.g. 0.3, 0.4, and 0.5, 0.6 etc.

This table of results shows the recordings.

The cumulative frequency was calculated by adding up the difference in resistance of each previous parameter.

This table of results shows how in general, providing the range bars are of the same difference in diameter, the thinner the wires in the range bar, the greater the change in resistance between them. By calculating the cumulative frequency of these results it becomes clear that this is the case because difference in resistance between each range becomes smaller because the loss of resistance is becoming less after a certain point. The results in the table do follow this idea generally however in detail the differences between some ranges do not follow the pattern. This is not because the idea is the error, but because the reading of the data is in error. When reading the results from the graph I rounded each reading to the nearest single figure. This meant that particularly towards the ranges which included thicker diameters, the results did not follow an exact pattern. This is due to the fact that some readings are close together and therefore were rounded up or down to the same reading of resistance. The markings on the graph show how several reading can be rounded up or down to the same value of resistance. It also shows graphically that the difference in resistance between wire with thinner diameters were bigger. This supports my claim also.

In order to manipulate the available data further and to greater the depth of the investigation, I used the mathematical equation of ‘pi × (radius, squared)’ = the area of the flat circle of the wire. This answer when multiplied by 100 (mm), gave the total area of the wire used in each test.  These results are shown on the table below.

The graph of area and resistance shows the relationship between the area of wire and its resistance, only when the wire is nichrome as used in this experiment. The graph indicates a similar pattern to the graph measuring diameter and resistance. The bigger that the area of wire is, the less the resistance of the wire is. This does not however indicate that every 10cm2 of wire has a certain amount of resistance because that is not the way in which the graph was calculated. This graph simply shows the resistance of an area of wire when it is 10cm long. Therefore the change in resistance of different areas shown on the graph is due to the change of diameter because the diameter is the only factor that changes throughout this data manipulation. The area indicating a higher resistance, only has a higher resistance because it has a smaller diameter. The length stays the same, but the change in area between each recording of wire is due to the change of diameter between the wires. This is the reason for the graph looking similar to the initial graph which showed the relationship of diameter and resistance.

A second graph displays 2 variables given using the results from the calculations shown above in the table. These two variables are the area of 10cm of nichrome wire on ‘Y’ axis, and the diameter of the same wire ‘X’ axis. The graph with a trend line shows that the larger the diameter of the wire, the larger the area of the wire. These results also are very accurate due to the fact that the only data used to calculate this data is the diameter of the wire, which was measured 3 times each for precision and accuracy. Calculations were the only other means of manipulating that data to give these results. Pi was multiplied by the radius (half of the diameter) squared. Then, the answer was multiplied by 100 (mm) (10cm), to give the final reading for area. Pi is never ending number used in mathematics to calculate area and circumference of circles. Its first digits 3 are 3.14.

As shown on the graph there is a slight bend in the trend line which implies that as the diameter of the wire increases, the rate of increase in area increases. In other words, the rate that the area increases with diameter is accelerating. This could be due to the fact that as diameter increases, the whole length of wire increases diameter. Therefore area accelerates when the rate of increase in diameter remains constant, because the bigger the diameter of the wire the bigger the increase in overall area because area is added to a larger surface area than it was to a previous diameter. In other words the bigger the diameter of the wire when increased, the more surface area needs to be filled to fulfill the diameter increase for the whole length of wire and therefore the more the added amount of area is.

Despite the fact that my lowest recording in this graph is of a diameter of 0.24mm, one would assume that the trend line would continue to curve down to point (0, 0) because clearly, if a wire has a diameter of 0, then it therefore cannot have an area because there is nothing of it. This can be proven by using the calculation: Pi times 0 squared =0. This is because 0 squared =0 and 3.14 times 0=0.

This graph is a reciprocal graph because it is a curve that is approached, but never reached by the graph... The curve is of the sort of y=a/x (‘y’=‘a’ over ‘x’). For example when ‘x’ is 2, ‘y’ should be 0.5. This is not the actual pattern; however the shape of the graph is similar to this. This type of line represents a line when neither ends of the line become straight, vertical or horizontal.

Secondly the second experiment concluded that the thinner that the nichrome wire is, the larger the resistance. This is also evidence to support my prediction. The prediction made concerning the relationship between resistance and diameter of the wire, was in fact correct also. After conducting further manipulation and analysis of the results from the second investigation, it became clear how resistance is affected by area of wire. Results indicate that the smaller the area of wire, the smaller the resistance, however this cannot be trusted because the larger the diameter as shown in experiment 2, the smaller the resistance, however the larger the diameter of a wire, the larger its area will be.

If more results and data were available, I could have expanded this investigation further to talk about how various wires with different diameters change resistance as voltages are changed. For example I could have recorded how resistance changes in a wire as voltage through the wire is increased. If I had access to this data I could have compared how resistance changes when various voltages are used. I could otherwise have recorded how resistance changes with heat to support the claim that heat causes an increase in resistance. These all could have been used to expand and develop the experiment further.

If I were to conduct this experiment again, I would try to include some of these additional sub-investigations. I would conduct an experiment concerning the relationship between heat in a wire and its resistance. I could conduct this experiment for various diameters and lengths of wire. I may also have conducted an experiment whereby various lengths of wire were tested to see how long it would take for wire of various lengths to heat up to a level that a certain change in resistance was achieved due to the heat. These all would have developed the investigation and made the conclusions all the more in depth and interesting.

There are a range of additional sets of data which could have been beneficial in improving the complexity and reliability of the investigation. To improve the reliability of the experiment, I could have taken more readings of the recordings of each length of wire. This would have meant that I could have calculated a more accurate mean and hade a more detailed range bar. I could have backed up statements by conducting tests challenging them. For example to back up the statement about heat in a wire causing its resistance to be higher, I could have conducted a test whereby a nichrome wire was used to record its resistance at different temperatures, otherwise I could have supported the statement that heat is built up when the circuit is left on over time. I could have done this by measuring resistance of a thin wire every 10 seconds, when the power is left constantly on at a high voltage. This could have given me more to write about and would have increased the complexity of the investigation.

Evaluation        

There was a small mistake in the conduction of the first experiment, which if not noticed, could have lead to major inaccuracies in the results of the data.  The mistake was that I read the current of the first experiment to be 56amps throughout the investigation. The ammeter was unclear about where the decimal place was and the actual reading was in fact 0.56amps. The results have now been changed by multiplying the resistance by 100. This has been checked several times for accuracy. This mistake was noticed when I realized, after I had calculated resistance, that 56amps in a wire of the diameter used would cause far too much resistance which would have lead to heat in the wire so much that the wire would have broken in two due to the heat. This I did not notice as I was conducting the experiment so my conclusion was that the amp recording must have been wrong. I re-calculated the resistance of each length of wire and spent some time checking my work for other inaccuracies. The likelihood if this is now minimal.

The apparatus in both experiments was carefully considered before any recording of data to prevent any bad recordings or unfair data. The length of copper wire in the circuit was kept to a minimum to prevent the loss of too much voltage as resistance. This would have made the test unfair. I also checked the position of the ammeter and voltmeter, they were in the positions shown on the circuit diagrams, I also check the wire for immediate heating effects. The power output setting was also checked before any recording. All of these precautions were taken in order to maximize the reliability and accuracy of the recorded data and to reduce the chance of any outliers (anomalous readings).

The safety of the experiment was purposefully kept to a maximum. The power packs had a block on them to prevent a voltage higher than 10v. This meant that it was reasonably safe to touch unprotected wire. The only other safety hazard could have been the high temperature of the wire. This was certainly the most hazardous factor of the entire investigation; however was not a major threat to safety of the investigation. It was controlled by using low voltages which prevented the wire from becoming dangerously over heated. A natural safety measure of the wire was that if it because too hot, it broke, thus breaking the connection of the circuit and allowing the wire to cool down.

As mentioned in the introduction, there were a few factors that could have affected the accuracy of the experiments and quality of results ( see figure 1 on page 3b, in the introduction section) , however as shown in the analysis in previous paragraphs, despite slight inaccuracy, the results are sufficiently trustworthy to be able to be analyzed in detail.

It would have possible for us to improve our investigation by heightening the accuracy of the results. This could have been done by repeating each recording more times. This would have given us more accurate mean. Due to the fact that the experiment was only conducted 3 times, the mean is not as accurate as is could have been. This could have affected the quality of the results. Despite this, the results show a high degree of accuracy because there is very little scatter in the results. Therefore the range bars are very small. This indicates a small range in data which leads to an indication of accuracy in the results and an accurate mean.

In the analysis of experiment 2, I mentioned the anomaly in the recording of current in set 1 of 2.85amps. This recording may have affected the accuracy of the results and could have lead to an unfair conclusion which would have reduced accuracy. I felt it necessary to deduct this result from the calculation of mean, to increase accuracy of the range bars in the graph, and quality of conclusion.

I have high confidence in the reliability of the conclusion, due to the accuracy of the results indicated and explained in the analysis of both investigations. The small range bars indicate a high degree of accuracy in the results. Secondly, the data of which I did not conduct an experiment for, but which I received from another source was also very accurate. This information was taken from the BBC GCSE Bitesize website which includes accurate information concerning resistance in wires. Assumptions and explanations made from this information, I have a great deal of confidence in. For example the explanation for the increase in size of range bars in experiment 1 was based on information from this source which can be relied on.

The first statement, concluded in the first experiment stated that resistance increases at a proportional rate that length of the wire is increased. This is because the longer that the wire is, the more particles of the metal element there are for the electrons to collide with, and so there are more they do collide with. This causes a small amount of friction per electron collision, which all adds up. This friction produces heat. The heat energy is energy transferred from electrical energy in the current. This transfer of energy means that there is less energy that remains as electrical energy. Therefore this removal of electrical energy is resistance. This resistance over a length of wire causes a change in electrical energy or voltage which I recorded as potential difference. The more potential difference that a wire has, the higher its resistance is.

The second conclusion was that taken from the results of the second experiment. It states that the larger the diameter of a wire, the less resistance it has, therefore the thinner the wire or the smaller its diameter, the more resistance it has. This is because a thicker wire allows more space for the same amount of electrons to flow through it and therefore mean that the amount of collisions between electrons I much higher. These collisions cause a lot of friction which causes a production of heat. The heat is transferred to the element or wire and causes the particles in the wire to vibrate; this creates more collisions because it makes it harder for the electrons to pass through. Therefore there is more friction, more heat transferred and a larger increase in resistance.

This investigation has clearly shown that resistance changes proportionally as length increases, and as diameter is increased, resistance rapidly decreases. These two statements are both supported by the results from the enclosed graphs and have been analyzing in their following paragraphs. These two statements also compliment my initial prediction which stated exactly that.

Due to the fact that there is very little scatter in my results, it gives me very little to right about in my conclusions. If the range bars had been bigger or had more scatter, I could have suggested reasons why the results were as they were and attempt to justify the inaccuracies using scientific terminology and detailed explanations or theories as to why the results were as they were. I have explained in detail the reason for the increase in the size of the range bars in the first experiment. Due to the fact that the scatter is so small in the second experiment there is very little to be mentioned. If the results had been inaccurate of had more scatter I could have critically discussed the cause for this.

Bibliography

I used the following websites only for research into resistance:

There was no other resource or external source of data used other than these. All other data was from the results of the experiments and knowledge of this subject.

Document Details

• Word Count 9978
• Page Count 24
• Subject Science

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Determination of the specific resistance of a wire using meter bridge

Meter Bridge is very easy and useful technique for measurement of unknown resistance. The resistance per unit length of meter bridge wire is determined using this technique. Resistivity of a wire is also measured by using this method.[1] The specific resistance of the giver wire is found 10.4 X 10-6 Ω-cm. with an error of 24.96%. This technique is very useful to determine unknown resistance and resistivity.

Related papers

In this paper the measurement of a resistance by means of a Wheatstone bridge in which the detector is a digital voltmeter (DVM) is investigated. The relationships for the determination of the Wheatstone bridge resistances in order to accurate measurement of a resistance are derived. To validate the derived relationships some experimental results are carried out.

International Journal of Engineering and Advanced Technology

Many devices have components that have very low ohmic properties. The resistances of these components should be measured to ensure their value doesn’t change. An overview is presented on precision resistance measurement for values less than 100Ω. Few techniques like Wheatstone bridge, current-voltage method, current comparators are discussed here.

American Journal of Scientific and Industrial Research, 2011

International Journal of Applied Mathematics, Electronics and Computers, 2015

Automatic Bridge Balance and Measurement of Resistance using Microcontroller (ABBMRM) is implemented effectively for balancing the Wheatstone bridge using the Microcontroller (8051) with higher accuracy.

Serbian Journal of Electrical Engineering, 2013

The paper presents the real instrument functional characteristics and describes the way of practical solutions of its performance improvement. It presents the design process of the instrument made for resistance measuring. In order to achieve desired objectives, a great number of experiments have been carried out during the development. Basically, the comparison method has been applied. At first, it was intended for the small resistor measuring as a single range unit. Later, the device has been improved and upgraded for a wide range resistance measuring. Finally, some of the difficulties have been detected and explained as well. The paper contains solutions developed and applied for their overcoming.

IEEE Transactions on Instrumentation and Measurement, 2000

-The procedure for the measurement of low ohmic resistance is developed;the indirect method is used, which allows to determine the best estimate of the magnitude of a low ohmic resistance without the need for a Kelvin bridge. Starting from Ohm's law and the four-terminal configuration of a resistor, the mathematical model that involves the readings of a voltmeter, an ammeter and a thermometer is developed; this model implies the correction by temperature at 20 [°C] of the measured magnitude. In addition, an experimental example and the numerical results obtained are shown.

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Materials Science and Engineering: A, 2007

Electronics And Electrical Engineering, 2011

MAPAN, 2011

Facta universitatis - series: Electronics and Energetics, 2019

International Journal of Engineering Research and Technology (IJERT), 2013

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Experimental Mechanics, 1992

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Measurement, 2017

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Electronics 

Ohm's law.

Ohm's law is a fundamental equation that shows how voltage, electrical current and electrical resistance are related in simple conductors such as resistors. This experiments allows you to explore Ohm's law and how the coloured bands on resistors codes their resistance. In doing this you will also learn how to use a power supply and 'digital multimeters'.

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• Quick Guide
• Full Instructions

Ohm’s law

Voltage , current and resistance are the most fundamental quantities for describing the flow of electricity . Ohm’s law shows how these three quantities are related and so is a powerful way of understanding the basic nature of electricity.

This is relevant to vast areas of technology today, including national electricity grids, power generation, design of all electronic devices and all electronic circuits, heating, electrical safety and understanding of natural phenomena such as lightning. This experiment will allow you to explore Ohm’s law by making measurements of voltage, current and resistance.

Resistors are the simplest and most commonly used electronic component and almost all electronic circuits contain them. They can be used to change the properties of any circuit they are part of, such as current flow , how voltage is distributed across components, the speed of a circuit , the amount of amplification from a circuit, the response of a sensor or the amount of electrical heating from a circuit.

The simplest resistors are made of a thin film or wound wire of carbon or metal . They usually have a series of coloured bands that represents both their target resistance value and how much the actual value might vary from this (the ‘ tolerance ’). This experiment lets you practise selecting the appropriate colour bands on a resistor to achieve a certain resistance value.

Digital Multimeters

Digital multimeters (DMMs) are versatile pieces of equipment commonly found in electronics, physics and engineering labs. In this experiment you’ll learn how to use a DMM to measure voltage , current and resistance . You’ll see this piece of equipment in many other FlashyScience experiments!

Use this experiment to find out more!

Download the file below for the quick guide for the  Ohm's Law  experiment (requires login) or follow these brief instructions:

To measure resistance:

• On the right-hand Digital Multimeter (DMM), rotate the switch to resistance measurement.
• Click and drag the clips on the wires attached to the right-hand DMM so that they snap to the wires either side of the resistor (make sure the power supply is turned off).
• Note the resistance value shown on the DMM screen.

To change the resistor:

• Click the resistor you wish to change to move to the  Selection  screen.
• Click on the colour band you wish to change.
• Click on the palette colour you wish to select.
• Click on the resistor wire to return to the main screen.

To use voltage and current:

• Turn on the power supply (right hand side of screen) and turn the dial to set the voltage.
• To measure  current through the resistor  – turn the  left-hand DMM  dial to DC current.
• To measure the  voltage across the resistor  – turn the  right-hand DMM  dial to DC voltage.
• NOTE: in this experiment the power supply voltage is also shown directly on its display.

​Download the file below for full instructions for the Ohm's Law  experiment (requires log in).

Download the files below for activities for the Ohm's Law  experiment (requires login).

• ACTIVITY 1: Investigate what the different coloured bands on resistors mean
• ACTIVITY 2: Learn how to use a DMM to measure electrical resistance
• ACTIVITY 3: Explore the effect of the tolerance band (band 4) on resistors
• ACTIVITY 4: Explore the statistics of resistance values from resistors with the same band colour coding
• ACTIVITY 5: Investigate Ohm’s law by measurement of voltage and current with a resistor
• ACTIVITY 6: Investigate Ohm’s law by measurement of current for different resistors with a fixed voltage
• ACTIVITY 7: Investigate Ohm’s law by measurement of voltage for different resistors with a constant current
• ACTIVITY 8: Investigate the power consumption due to electricity flowing in a single resistor
• ACTIVITY 9: Investigate the power consumption due to electricity flowing through different resistances

(Available as separate downloads or all activities)

*NEW* Now also available in editable Microsoft Word format

Download the file below for the background science behind the Ohm's Law  experiment (requires log in).

Potential Divider

A potential divider is a simple circuit that uses resistors to supply a variable 'potential difference' (i.e. voltage).This can be used for many applications, including control of temperature in a fridge or as audio volume controls. Understanding how the resistors in the circuit allow this is important for designing many electronic circuits. Here you can investigate how changes in the two resistors can lead to different voltages across them. 

Most electrical or electronic circuits use the voltage across the circuit components to perform some task. This includes motors, sensors, speakers, computer chips, LEDs and diode lasers, communications antennas (e.g. in mobile phones), heaters, turbines, and mains electricity delivery to houses and industry.

It is important to know how to control the voltages in these circuits to make the applications work! The simplest circuit to start to understand this is the  potential divider , which is made up of two resistors in series . Other circuits may be made of more advanced components but often use the same principles of voltage (i.e. ‘potential’) division. For example: two  transistors  in opposite high or low resistance states and connected in series are used to define whether a ‘ logic gate ’ is set to a digital ( Boolean ) value of 1 or 0, and are a fundamental building block of how a digital computer processor works.

Sensors can be made from a fixed resistor and a component that has a resistance that depends on whatever is being sensed connected, e.g. a  thermistor  for sensing heat or a  light-dependent resistor  for sensing light. A voltage applied to the two components in series allows the voltage across the fixed resistor to be a measure of the resistance of the sensing element’s resistance. This approach can avoid some difficulties of just using the single element, such as high power consumption.

Electrical heaters (including room heaters, cookers and hair dryers) use a fixed resistance   heating element  (e.g. a coil of wire) and a variable resistance   transistor  in series. The resistance of the transistor then controls how much voltage is across the heating element and, therefore, how much electrical heating is produced!

This experiment allows you to gain a good understanding of the  potential  divider . It also allows you to reinforce your understanding of  Ohm’s law , how  resistor  coloured bands code for resistance, and how to use  digital multimeters  (DMMs), which you may have already met in the FlashyScience  Ohm’s L aw  experiment.

​Download the file below for the quick guide for the  Potential Divider  experiment (requires login) or follow these brief instructions:

• On the right-hand Digital Multimeter (DMM) rotate the switch to resistance measurement.
• Click and drag the clips on the wires attached to the right-hand DMM so that they snap to the wires either side of either or both resistors (make sure the power supply is turned off).

To change a resistor:

To measure voltage and current:

• NOTE: the output voltage of the power supply is also shown on its display.

Download the file below for full instructions for the Potential Divider  experiment (requires log in).

Download the file below for activities for the Potential Divider  experiment (requires login).

• ACTIVITY 1: Investigate how the resistances of resistors in series combine
• ACTIVITY 2: Investigate how the current in a potential divider is controlled
• ACTIVITY 3: Explore how voltage in a potential divider depends on the resistor values
• ACTIVITY 4: Consider the voltage ratios across resistors in a potential divider
• ACTIVITY 5: Achieve certain voltages by changing the resistor values
• ACTIVITY 6: Explore power consumption in a potential divider
• ACTIVITY 7: Achieving particular property values in potential dividers
• ACTIVITY 8: Design a potential divider heating element
• ACTIVITY 9: Design a volume control element
• ACTIVITY 10: Design a sensor circuit

Download the file below for the background science behind the Potential Divider  experiment (requires log in).

Resistivity of a Wire

The electrical resistivity of a wire tells us how well the wire material conducts electricity. This is crucial information for any application that involves conducting electricity, including wind turbines, electric vehicles, household electrical goods and computers. Here you can measure the resistivity of wires of different materials and widths, and consider which would be best suited for conducting electricity.

Electronic materials are crucial to our life today , and electrical ‘resistivity’ tells us how good or poor a material is at conducting electricity.

We use materials with low electrical resistivity to transmit electrical power from generators, across grid distribution networks , and to homes and workplaces for use . Designers of electrical devices rely on knowing the resistivity of wire used in order to calculate the resistance of components.

These devices range in size from enormous machines such as wind turbines or industrial lifting equipment ; motors or engines in electric vehicles and all-new electric aircraft ; consumer products such as washing machines, hair dryers and ovens ; and the nanoscale components within the computer chips found in smart devices, laptops, and mobile phones .  

In fact, modern computing is based on controlling the resistivity of semiconductor materials in a type of transistor (known as ‘field effect transistors’ using ‘CMOS’ technology).

Measuring electrical resistivity helps us to understand the properties of materials, to monitor manufacturing processes, and to select the best material for an application.

Download the file below for the quick guide for the  Resistivity of a Wire  experiment (requires login) or follow these brief instructions:

• Click on the right hand wire post to move to the  Select Wire  screen.
• Open the micrometer by dragging the thumbwheel down.
• Choose a material and drag the unlabelled wire into the micrometer.
• Close the micrometer and measure the wire's width.
• Click on the wire while it's in the micrometer to return to the  main screen .
• Click on the switch to turn it on.
• Measure voltage and current for a variety of contact positions on the wire.
• Calculate resistance for each contact position. 
• Plot resistance vs contact position and calculate the gradient of a line of best fit.
• Multiply the line's gradient by the wire's cross-sectional area to obtain the wire's electrical resistivity.

Download the file below for full instructions for the Resistivity of a Wire  experiment (requires log in).

Download the file below for activities for the Resitivity of a Wire  experiment (requires login).

• QUICK ACTIVITIES: 5 quick activities to try
• ACTIVITY 1: Different wire lengths

(Available as separate downloads or all activities)

Download the file below for the background science behind the Resitivity of a Wire  experiment (requires log in).

IV Characteristics of Devices

An 'IV characteristic' of a device shows how the electrical current in the device changes with applied potential difference. The IV characteristic is linear for some devices and nonlinear for others. This experiment allows you to explore the IV characteristics of resistors, a filament lamp and diodes by changing and measuring potential difference and current. 

Electricity powers the modern world. It is essential for electronic devices, home appliances, travel and school, work and leisure.

The widespread use of electricity is because we can make so many components that have different electrical behaviours, and then combine them to make all sorts of devices and machines. These behaviours can be seen most easily by creating a graph of the electrical current ( I ) through a component against the potential difference ( V ) placed across it. This graph is known as a component’s IV characteristic .

The simplest component is the electrical resistor . These have fixed electrical resistance , which means the electrical current is proportional to the potential difference and the IV characteristic is linear . Resistors are vital to almost all electrical devices, from a mobile phone to the world’s most powerful supercomputer, a flashlight to electric vehicles, an electric toothbrush to a medical scanner, your internet router to a communications satellite, or a vacuum cleaner to air-conditioning.

Diodes  are made of two different semiconductor materials joined together and only allow electricity to flow in one direcion through them. They are hugely important in electronics and electrical engineering. They are most often used to convert alternating current (AC) electricity to direct current (DC), for example to convert mains electricity into 12 V DC used for charging mobile devices. They are also widely used to protect electronic circuits by preventing unwanted currents. 

Filament lamps might not be used for lighting as much as they once were but they show interesting electrical effects. They contain a long, thin metal 'filament' that heats up when high electrical current is flowing, which results in it starting to glow and give off light. The heating also changes the filament's electrical resistance, which results in a non-linear IV characteristic .

This virtual experiment will allow you to explore the electrical behaviour of resistors, diodes and filament lamps. You can take measurements of current and potential difference, plot a graph of their IV characteristics, and find their resistance values .

Download the file below for the quick guide for the IV Characteristics of Devices  experiment (requires login).

Download the file below for full instructions for the IV Characteristics of Devices  experiment (requires log in).

Download the files below for activities for the IV Characteristics of Devices  experiment (requires login).

• ACTIVITY 1: IV characteristics of resistors
• ACTIVITY 2: IV characteristic of a filament lamp
• ACTIVITY 3: IV characteristic of a diode
• ACTIVITY 4: Power consumption of resistors (advanced)
• ACTIVITY 5: Power consumption of  a filament lamp (advanced)

(Available as separate downloads or all activities)

Download the file below for the background science behind the IV Characteristics of Devices experiment (requires log in).

Resistance (of a wire)

Understanding the electric resistance of metal wires is fundamental to being able to design electrical machines and electronic devices. In this experiment, you can vary the effective length of a wire by moving an electrical contact and then go on to measure the wire's electric resistance by measuring potential difference and electric current on analogue dials. 

Electricity powers so much of our life today. We use metal wires to transmit electrical power from power generators, such as power stations, ‘PV’ (photovoltaic) devices and wind turbines, to our homes and workplaces.

We use ‘ resistance ’ to measure how easily materials allow electrical current to flow. It is vital to the design of power distribution networks over long distances to understand how the length of a metal wire affects its resistance.

On smaller scales, it is important to know how the length of a conducting wire changes its resistance for applications that use motors , from washing machines through to electric cars and industrial machines . Electricity is also used in heaters , from industrial furnaces for large-scale materials processing through to ovens, underfloor heating and kettles, and in all sorts of electronic devices , such as computers , screens and sensors .

Designing any of these applications to be efficient and effective requires understanding how electricity flows through the materials in the various devices.

Download the file below for the quick guide for the Resistance (of a wire)  experiment (requires login).

Download the file below for full instructions for the Resistance (of a wire)  experiment (requires log in).

Download the files below for activities and associated worksheets for the Resistance (of a wire ) experiment (requires login).

• ACTIVITY 1: Effect of wire length on its resistance
• ACTIVITY 2: Effect of wire width on its resistance
• ACTIVITY 3: The resistance of different materials

(Available as separate downloads or all activities/all worksheets)

Download the file below for the background science behind the Resitance (of a wire) experiment (requires log in).