Question

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

Answer 1

Ohm's law:

1. 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.
2. Mathematically, it is stated as below: $V=IR$
3. where V is the voltage across the resistor R and I is the current passing through it.
4. Ohm's law can easily be verified by implementing the following circuit:

Procedure:

1. Set up a circuit as shown.
2. Vary the voltage across the resistor using a potentiometer or a rheostat in series with the supply.
3. Measure the voltage and the corresponding current for various voltages applied using a voltmeter and ammeter respectively.
4. Then calculate the ratio of all the voltages to their corresponding currents (V/I).
5. It will be observed that the resistance offered will be observed to be the same.

Ohm's does not hold good under all conditions:

If a graph of Voltage vs Current is plotted, the curve is found to be linear as shown below:

The slope of this curve is the resistance R. Since, the curve obtained is linear, the slope at every point on the curve is constant, which implies that the resistance R is constant.

Ohm's law holds only when all the physical and environmental variables remain constant. Resistors could vary if local environment temperatures are changed during the experiment, and hence Ohm's law will not be valid.