NCERT · Class 10 · Science · ElectricityState Ohm's law. Describe an activity to verify Ohm's law experimentally. Draw a labeled circuit diagram and the expected V-I graph.

Ohm's Law\nOhm's law states that the electric current flowing through a metallic wire is directly proportional to the potential difference $V$ across its ends, provided its temperature remains constant.\nMathematically: $V \propto I$ or $V = IR$, where $R$ is resistance.

Experimental Verification\nTo verify Ohm's law, we set up an electric circuit.

Apparatus Required

• A resistance wire (or resistor)
• An ammeter (to measure current)
• A voltmeter (to measure potential difference)
• A battery or cell
• A plug key
• Connecting wires

Circuit Diagram and Setup

1. Connect the resistance wire in series with the ammeter, battery, and plug key.
2. Connect the voltmeter in parallel across the ends of the resistance wire.
3. Ensure the positive terminals of both meters are connected to the positive terminal of the battery.

Procedure

1. Close the key so that current starts flowing in the circuit.
2. Note down the reading of the ammeter ($I$) and the voltmeter ($V$).
3. Introduce one more cell in the circuit to change the potential difference. Note down the new readings of $V$ and $I$.
4. Repeat this process by using different numbers of cells one by one.
5. Calculate the ratio $V/I$ for each set of readings.

Observations and Calculations

• It is observed that the ratio $V/I$ is nearly constant for all readings.
• When a graph is plotted between the potential difference ($V$) along the x-axis and current ($I$) along the y-axis, we obtain a straight line passing through the origin.

Conclusion\nThis straight line graph confirms that current is directly proportional to the potential difference, thus verifying Ohm's law.