Lesson 2, Topic 2
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# Experimental Verification of Ohm’s Law

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Aim of Experiment: To verify ohm’s law.

Apparatus: Ammeter, voltmeter, rheostat, standard resistor, cell, connection wires and switch.

Set-up Diagram: The connection diagram for verification of Ohm’s law is shown below.

Procedure:

A conductor of resistance R ohms is connected in series with an ammeter A, rheostat (variable resistance) and a battery B through key K. To measure the potential difference across the resistance, voltmeter V is connected across the ends of the resistor.

Press Key K to close the switch so that current flows in the circuit.

Read and record the values of current that flow in the circuit and voltage across the resistor using an ammeter and voltmeter respectively.

After relapsing the key K adjust the rheostat to a new position so as to change the resistance of the circuit. Close the switch by pressing Key K again. Record the new voltmeter and ammeter readings.

Repeat the process at least three more times. Read and record the corresponding values of I and V recorded by the ammeter and voltmeter.

Results

### Graph of Voltage V Against Current I:

The different values of Voltages V that were obtained are plotted on the vertical axis against different values of current I on the horizontal axis. A straight line graph which passes through the origin is obtained as shown below.

From the observations, it will be found that the ratio of voltmeter reading and ammeter reading remains the same i.e.

$$\frac{V_1}{I_1} = \frac{V_2}{I_2} = \frac{V_3}{I_3} = \frac{V_4}{I_4} = \frac{V_5}{I_5}$$

Constant = R, the resistance of the conductor.

The slope of the graph represents the resistance as shown below.

Slope = $$\frac{V_2 \: -\: V_1}{I_2 \: – \: I_1} \\ = \frac{Voltage}{Current}$$

R = $$\frac{Voltage}{Current}$$

Therefore, Slope = Resistance.

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