A wire has a resistance of \( 2.1\,\Omega \) at 25°C and a resistance of \( 2.8\,\Omega \) at 100°C. The temperature coefficient of the resistance is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( 4.4\times10^{-3}\,{}^{\circ}\mathrm{C}^{-1} \)
The temperature coefficient of resistance \( \alpha \) is the fractional change in resistance per degree rise in temperature. Taking the resistance at 25°C as the reference:
\( \displaystyle R_2 = R_1\left[1 + \alpha\,(T_2 - T_1)\right] \;\Rightarrow\; \alpha = \frac{R_2 - R_1}{R_1\,(T_2 - T_1)} \)
\( R_1 = 2.1\,\Omega,\ T_1 = 25^{\circ}\mathrm{C} \)
\( R_2 = 2.8\,\Omega,\ T_2 = 100^{\circ}\mathrm{C} \)
\( \displaystyle \alpha = \frac{2.8 - 2.1}{2.1 \times (100 - 25)} = \frac{0.7}{157.5} \approx 4.4\times10^{-3}\,{}^{\circ}\mathrm{C}^{-1} \)
Note: NTA picked this question from an NCERT (2026-27) exercise and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
Exercises – …
