On the basis of variation of resistivity with temperature, identify the correct statements in the following.
A. Resistivity of materials like Nichrome has a very weak dependence on temperature.
B. Resistivity of a conductor increases with increase in temperature.
C. Resistivity of a conductor decreases with increase in temperature.
D. Resistivity of a semiconductor increases with increase in temperature.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A and B only
How resistivity changes with temperature depends on whether heating mainly changes the relaxation time (metals) or the number of charge carriers (semiconductors).
(A) Resistivity of materials like Nichrome has a very weak dependence on temperature. — Correct. Alloys such as nichrome, manganin and constantan have a very small temperature coefficient, which is why they are used in standard resistors and heating elements.
(B) Resistivity of a conductor increases with increase in temperature. — Correct. In a metal the electron density is fixed; heating makes collisions more frequent, the relaxation time falls, and \( \rho = m/(ne^{2}\tau) \) rises.
(C) Resistivity of a conductor decreases with increase in temperature. — Incorrect. This is the opposite of (B).
(D) Resistivity of a semiconductor increases with increase in temperature. — Incorrect. In a semiconductor the carrier density rises sharply on heating, so its resistivity decreases.
NCERT (2026-27):
Temperature Dependence of Resistivity – “… Some materials like Nichrome (which is an alloy of nickel, iron and chromium) exhibit a very weak dependence of resistivity with temperature (Fig. 3.9). … Unlike metals, the resistivities of semiconductors decrease with increasing temperatures. … In a metal, \( n \) is not dependent on temperature to any appreciable extent and thus the decrease in the value of \( \tau \) with rise in temperature causes \( \rho \) to increase as we have observed.”