Question

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

Answer 1

According to Ohm law on constant temperature the current passing through conductor is directly proportional to the potential difference across it's end's.

Mathematically we can write:

$I\propto V$

or $I=VR$

Here, constant R is known as the Resistance of given conductor.

For a given conductor it's Resistance is constant at a given temperature.

One can verify Ohm's law by following Experiment:

The circuit Diagram of the experimental set up has been shown.

Here, XY is the Resistance wire, A an Ammeter and V an Voltmeter.

A battery of 4 cells is being used as a current source and K is a Plug Key.

Step 1:

Initially use one cell only. Put Plug in Key K and note current an voltage by noting Ammeter and Voltmeter reading respectively. Let these be $I_1$ and $V_1$

Step 2:

Then connect the two cell's in the circuit and note current $I_2$ and potential Difference $V_2$ across the resistance.

Step 3:

Similarly, take reading's with $3$ and $4$ cell's in the circuit.

From the observation's we find that

$V_1/I_1=V_2/I_2=V_3/I_3=V_4/I_4=\text{constant}=R$

If we Plot V-I Graph comes out to be a straight line. It experimentally verifies Ohm's law.

No, It doesn't hold under conditions like non-constant temperature and pressure.

It is true for conductors only.