experiment on verification of ohm's law

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

Aims of the ohm’s law experiment are as followings –

• Verification of Ohm’s Law by showing that the Voltage to Current ratio is constant.
• To determine the resistance of a wire by plotting a graph for potential difference (V) versus current (I) using Ohm’s Law.
• To find the resistivity of a wire by plotting a graph for potential difference versus current.

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)

Where I is current, V is the potential difference and R is the resistance.

Again, the formula for the resistance of a wire is, \color{Blue}R=\frac{\rho L}{A}

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.

In this experiment, we will find the current and the potential difference across the sample wire by using Ammeter and Voltmeter respectively. Then the resistance of the wire can be found by using equation (1).

Again, We have to take at least five sets of data for different voltages and currents. Then a graph is needed to plot the current along the positive Y-axis and the potential difference along the positive X-axis.

• Ohm’s Law can be verified by finding the Voltage to current ratio. If the ratio remains constant [equation- (1)] for all sets of data, then we can say that the voltage across the resistance is proportional to the current through it which is nothing but Ohm’s Law.
• One can easily find the value of resistance of the wire from the slope of the graph. R = \frac{V}{I}
• One can find the resistivity of the wire from equation (2) by using the value of R from the graph. Usually, the examiner supplies the radius (r) or diameter (2r) and length (L). If radius and Length are not given then we have to find those by using a screw gauge and meter scale respectively.

Apparatus Used

The apparatus used for this experiment –

• A power supply (Voltage source or Battery): The used battery can supply the voltage from 0 to 12 volts.
• An Ammeter (A) to measure current. This Ammeter can measure the current from 0 to 3 amperes.
• A Voltmeter (V) to measure Voltage. The used Voltmeter can measure the voltage from 0 to 3 volts.
• A rheostat controls and adjusts the current through the circuit.

Circuit Diagram

Fig. (1) gives the circuit diagram for the verification of Ohm’s Law lab experiment.

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

The formulae used for the Ohms law lab work are

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

Experimental data

The least count of Ammeter = Smallest division of Ammeter = 0.05 ampere

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

So, we can see that in each observation the voltage-to-current ratio is almost the same. Thus, the voltage across the wire is proportional to the current through the wire. Hence Ohm’s law is verified .

Now we got the calculated value of the resistance of the wire is R = 1.02 ohm.

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

Discussions

• When the voltage V = 0, the reading of the ammeter is zero. That means the current through the wire is zero. Now, one cannot calculate the resistance for this data because one cannot measure the opposition faced by the current until the current flows.
• In the last two data, the current has not increased as much as first three observations. This is because of the increase in resistance of the wire due to heating. Here current flow through the wire causes joule’s heating.
• The calculated value of resistance almost matches the resistance calculated from the graph.
• If the radius (r) and length (L) of the wire are not supplied, then we have to determine those parameters by screw gauge and the meter scale respectively.
• In this experiment 1) verification of ohm’s law is done 2) Unknown resistance of the wire and 3) Resistivity of the material of the wire is determined.

This is all from this post on experimental verification of ohm’s law. If you find this post helpful, share it with your classmates and friends.

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• Current Electricity

Ohm’s law states the relationship between electric current and potential difference. The current that flows through most conductors is directly proportional to the voltage applied to it. Georg Simon Ohm, a German physicist was the first to verify Ohm’s law experimentally.

Ohm’s Law Explanation

One of the most basic and important laws of electric circuits is Ohm’s law.

Ohm’s law states that the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperatures remain constant.

Mathematically, this current-voltage relationship is written as,

In the equation, the constant of proportionality, R, is called Resistance and has units of ohms, with the symbol Ω.

The same formula can be rewritten in order to calculate the current and resistance respectively as follows:

Ohm’s law only holds true if the provided temperature and the other physical factors remain constant. In certain components, increasing the current raises the temperature . An example of this is the filament of a light bulb, in which the temperature rises as the current is increased. In this case, Ohm’s law cannot be applied. The lightbulb filament violates Ohm’s Law .

Relationship Between Voltage, Current and Resistance

Water Pipe Analogy for Ohm’s Law

Ohm’s Law describes the current flow through a resistance when different electric potentials (voltage) are applied at each end of the resistance . Since we can’t see electrons, the water-pipe analogy helps us understand the electric circuits better. Water flowing through pipes is a good mechanical system that is analogous to an electrical circuit.

Here, the voltage is analogous to water pressure, the current is the amount of water flowing through the pipe, and the resistance is the size of the pipe. More water will flow through the pipe (current) when more pressure is applied (voltage) and the bigger the pipe (lower the resistance).

The video below shows the physical demonstration of the Waterpipe analogy and explains to you the factors that affect the flow of current

Experimental Verification of Ohm’s Law

Ohm’s Law can be easily verified by the following experiment:

Apparatus Required:

• Initially, the key K is closed and the rheostat is adjusted to get the minimum reading in ammeter A and voltmeter V.
• The current in the circuit is increased gradually by moving the sliding terminal of the rheostat. During the process, the current flowing in the circuit and the corresponding value of potential difference across the resistance wire R are recorded.
• This way different sets of values of voltage and current are obtained.
• For each set of values of V and I, the ratio of V/I is calculated.
• When you calculate the ratio V/I for each case, you will come to notice that it is almost the same. So V/I = R, which is a constant.
• Plot a graph of the current against the potential difference, it will be a straight line. This shows that the current is proportional to the potential difference.

Similar Reading:

• Kirchhoff’s Law
• Faraday’s Laws
• Laws of Thermodynamics

Ohm’s Law Magic Triangle

Ohm’s Law Solved Problems

Example 1: If the resistance of an electric iron is 50 Ω and a current of 3.2 A flows through the resistance. Find the voltage between two points.

If we are asked to calculate the value of voltage with the value of current and resistance, then cover V in the triangle. Now, we are left with I and R or more precisely I × R.

Therefore, we use the following formula to calculate the value of V:

Substituting the values in the equation, we get

V = 3.2 A × 50 Ω = 160 V

Example 2: An EMF source of 8.0 V is connected to a purely resistive electrical appliance (a light bulb). An electric current of 2.0 A flows through it. Consider the conducting wires to be resistance-free. Calculate the resistance offered by the electrical appliance.

When we are asked to determine the value of resistance when the values of voltage and current are given, we cover R in the triangle. This leaves us with only V and I, more precisely V ÷ I.

R = 8 V ÷ 2 A = 4 Ω

Calculating Electrical Power Using Ohm’s Law

The rate at which energy is converted from the electrical energy of the moving charges to some other form of energy like mechanical energy, heat energy, energy stored in magnetic fields or electric fields, is known as electric power. The unit of power is the watt. The electrical power can be calculated using Ohm’s law and by substituting the values of voltage, current and resistance.

Formula to find power

What is a Power Triangle?

The power triangle can be employed to determine the value of electric power, voltage and current when the values of the other two parameters are given to us. In the power triangle, the power (P) is on the top and current (I) and voltage (V) are at the bottom.

Ohm’s Law Pie Chart

Ohm’s Law Matrix Table

Ohm’s Law Applications

The main applications of Ohm’s law are:

• To determine the voltage, resistance or current of an electric circuit.
• Ohm’s law maintains the desired voltage drop across the electronic components.
• Ohm’s law is also used in DC ammeter and other DC shunts to divert the current.

Limitations of Ohm’s Law

Following are the limitations of Ohm’s law:

• Ohm’s law is not applicable for unilateral electrical elements like diodes and transistors as they allow the current to flow through in one direction only.
• For non-linear electrical elements with parameters like capacitance, resistance etc the ratio ofvoltage and current won’t be constant with respect to time making it difficult to use Ohm’s law.

The video about conductance, resistance, and ohm’s law

Frequently Asked Questions – FAQs

What does ohm’s law state.

Ohm’s law states that the current through a conductor between two points is directly proportional to the voltage across the two points.

What can Ohm’s law be used for?

Ohm’s law is used to validate the static values of circuit components such as current levels, voltage supplies, and voltage drops.

Is Ohm’s law Universal?

No. Ohm’s law is not a universal law. This is because Ohm’s law is only applicable to ohmic conductors such as iron and copper but is not applicable to non-ohmic conductors such as semiconductors.

Why is Ohm’s law not applicable to semiconductors?

Ohm’s law doesn’t apply to semiconducting devices because they are nonlinear devices. This means that the ratio of voltage to current doesn’t remain constant for variations in voltage.

When does Ohm’s law fail?

Ohm’s law fails to explain the behaviour of semiconductors and unilateral devices such as diodes. Ohm’s law may not give the desired results if the physical conditions such as temperature or pressure are not kept constant.

Watch the video and solve important questions in the chapter Electricity Class 10

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

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Learn all about Ohm's law

Ohm’s Law Lab Report [With Graph, Observations and Verification]

Ohm’s law is the fundamental law of Electrical Engineering. It relates the current flowing through any resistor to the voltage applied to its ends. According to the statement: The current flowing through a constant resistor is directly proportional to the voltage applied to its ends. This article presents the complete  Ohm’s law  Lab report and various questions regarding the lab. The latter portion simplifies the law for beginners by delineating the absolute basic concepts for beginners.

Objectives of Ohms Law Lab report

To verify that voltage and current are directly proportional using a 1kΩ resistor.

List of Components

• Variable DC Power supply
• 1kΩ resistor (Color code Brown, Black, Red, Gold)
• Connecting wires (Jumper wires)

Circuit Diagram

Setup the circuit diagram as shown below:

• Implement the circuit on the breadboard as shown in circuit diagram.
• Initially set the VDC supply to 0 V and note the current on ammeter.
• Increase the voltage to 1 V, observe the ammeter and note the readings.
• Repeat the above step for 2 V, 3V … 10 V.
• Plot a graph for measured readings.
• Compare the plot with theoretical calculations.

Observation table

Calculations [Verification of Ohm’s law report]

The theoretical calculations are achieved from the original formula, V = IR. You can also verify them from the  basic Ohm’s law calculator .

Graph for Ohm’s Law Lab report

The real (practically calculated – red color) vs the theoretical values (blue) are plotted on the graph. While most theoretical values are identical to practical values, one might note a difference of red dot for 2.99 mA and 6.99 mA.

Conclusion from Ohm’s Law lab Report

We learned that current and voltage hold a direct relationship for resistive components. (They are linearly proportional).

Basic Questions for Ohm’s Law Lab Report

Question: What is Variable DC supply?

Answer: A variable DC (direct current) supply provides variable output voltages. It contains a rotary knob which can be rotated to achieve our desired output voltages. Its symbol is similar to dc battery with the difference of an arrowhead over it.

Question: What is ammeter?

Answer: It is the current measuring instrument which is used in series to the circuit. It measures current and displays the amperes on LCD.

Question: What is the resistor, and what is resistor color coding?

Answer: Resistor is an electrical component which is used to control the flow of electrical current. Carbon resistors are the most commonly available type of resistors. They have color bands over their bodies which are used to identify the amount of resistance they possess.

Question: What are jumper wires?

Answer: They are special types of wires which can be easily mounted and used on the breadboards.

Question: Is Ohm’s Law important to learn?

Answer: Yes Ohm’s law is a fundamental law of Electrical Engineering and it’s very important. You can easily learn each and everything about the law from our website.

Question: Why practical results are different from theoretical results?

Answer: While no scientific-practical can perfectly match the theory, the actual results depend on environmental conditions, the accuracy of equipment under test. The quality of resistor also impacts the measurements, while in our lab report we got excellent results, you might get different results based on your theory.

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