Question

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

Answer 1

Hint: As we know the ohm’s law gives a relation between the voltage applied and the flow of current in a circuit. There are certain limitations to this law, which will be verified by an experiment. Further, the experiment will give us the required answer.

Formula used:
$\eqalign{& I \propto V \cr
  & I = \dfrac{V}{R} \cr} $

Complete step-by-step solution
According to Ohm's law on the constant temperature, the current “I” passing through the conductor is directly proportional to the potential difference V across its ends.
$\eqalign{& I \propto V \cr
  & I = \dfrac{V}{R} \cr} $
We can verify ohm’s law experimentally as:
The circuit diagram of the experimental setup is shown in the figure. Here, XY is the Resistance wire, A represents an Ammeter and V represents the Voltmeter. A battery of 4 cells is being used as a current source and K is a Plug Key.

1). Initially use one cell only. Put Plugin Key K and note current and voltage by noting Ammeter and Voltmeter reading respectively. Let these be $I_1$​ and $V_1$​.
2). Then connect the two cells in the circuit and note current $I_2$ ​and potential difference $V_2$​ across the resistance.
3). Similarly, we can take readings with the third and fourth cells given in the circuit.
4). Now, from the observations we find that
$\dfrac{{{V_1}}}{{{I_1}}} = \dfrac{{{V_2}}}{{{I_2}}} = \dfrac{{{V_3}}}{{{I_3}}} = \dfrac{{{V_4}}}{{{I_4}}} = const. = R$
If we Plot V-I Graph comes out to be a straight line. It experimentally verified Ohm's law.

So, we can say that ohm’s law doesn't hold under all conditions like non-constant temperature and pressure.
Therefore, ohm’s law is true for conductors only.

Additional information:
The valence band and conduction band of conductors overlap each other, which makes it easy for the electrons to transfer from one band to another, thereby making them good conductors of electricity and heat as well. Whereas the gap between the valence band and conduction band in an insulator is very large, this cannot be overcome by the electrons, thereby making them bad conductors of electricity and heat.

Note: There are limitations to Ohm’s law. They are valid only for conductors not for all materials. We should also note that resistance is inversely proportional to the flow of current. The unit of resistance is the ohm, named after the scientist.