Question

State Ohm’s law? How can it be verified experimentally? Does it hold good under all conditions? Comment on it.

Answer 1

Ohm's law states that the electrical current (I) flowing in a circuit is proportional to the voltage (V) and inversely proportional to the resistance (R). Therefore, if the voltage is increased, the current will increase provided the resistance of the circuit does not change.
$I=\frac{V}{R}$
Experimental Verification -
Apparatus: Rheostat, Ammeter, Voltmeter, Voltage supply of 5V D.C
Procedure:
1. Connect the variable voltage supply to both the ends of the rheostat.
2. Connect the ammeter in series with the rheostat.
3. Connect the voltmeter in parallel with the rheostat.
4. Start measuring the voltage and current as you move the rheostat, moving the hand from minimum position to the maximum position in the steps of constant increase in current.
5. Plot a graph between the voltage and the current using the data obtained by the experiment.
6. Observe the graph obtained.

The graph verifies ohm’s law.
Ohm’s law does not hold for all conditions. Ohm's law fails in semiconductor devices like a diode or a transistor, as in there the current flowing through the device is not proportional to the applied voltage across its terminals.