Current Electricity Question 5
Question 5 - 2024 (01 Feb Shift 2)
To measure the temperature coefficient of resistivity $\alpha$ of a semiconductor, an electrical arrangement shown in the figure is prepared. The arm $BC$ is made up of the semiconductor. The experiment is being conducted at $25^{\circ} C$ and resistance of the semiconductor arm is $3 m \Omega$. Arm BC is cooled at a constant rate of $2^{\circ} C / s$. If the galvanometer $G$ shows no deflection after $10 s$, then $\alpha$ is :
(1) $-2 \times 10^{-2 \circ} C^{-1}$
(2) $-1.5 \times 10^{-2 \circ} C^{-1}$
(3) $-1 \times 10^{-2 \circ} C^{-1}$
(4) $-2.5 \times 10^{-2}{ }^{\circ} C^{-1}$
Show Answer
Answer: (3)
Solution:
For no deflection $\frac{0.8}{1}=\frac{R}{3}$
$\Rightarrow R=2.4 m \Omega$
Temperature fall in $10 s=20^{\circ} C$
$\Delta R=R \alpha \Delta t$
$\alpha=\frac{\Delta R}{R \Delta t}=\frac{-0.6}{3 \times 20}$
$=-10^{-2} \mathbf{C}^{-1}$
