The materials and devices do not obey Ohm's law when(A) The relation…

The correct answer is Option (2) → (A), (B) and (C) only

A material obeys Ohm's law when \( V = IR \) with a constant \( R \): the V-I graph is a single straight line through the origin, the same for both directions of current. Any departure from this makes the material or device non-ohmic.

(A) The relation between \( V \) and \( I \) is not unique, i.e., there is more than one value of \( V \) for the same current \( I \) — Correct. If one current corresponds to more than one voltage (as in a GaAs device), \( V/I \) is not a single constant, so Ohm's law fails.

(B) The relation between \( V \) and \( I \) depends on the sign of \( V \) — Correct. A diode conducts easily one way and hardly at all the other way; reversing \( V \) does not just reverse \( I \), so it is non-ohmic.

(C) \( V \) ceases to be proportional to \( I \) — Correct. A non-linear V-I graph (for example a filament lamp at high current) means \( R \) is not constant.

(D) The relation between \( V \) and \( I \) is linear — Incorrect. A linear relation is exactly what Ohm's law describes; it is the condition for obeying the law, not for departing from it.

NCERT (2026-27):
Limitations of Ohm’s Law – “Although Ohm’s law has been found valid over a large class of materials, there do exist materials and devices used in electric circuits where the proportionality of V and I does not hold. The deviations broadly are one or more of the following types: (a) V ceases to be proportional to I (Fig. 3.5). (b) The relation between V and I depends on the sign of V.”

Limitations of Ohm’s Law – “… (c) The relation between V and I is not unique, i.e., there is more than one value of V for the same current I (Fig. 3.7).”