To measure the temperature coefficient of resistivity α of a semiconductor, an electrical arrangement shown in the figure is prepared. The arm BC is…

To measure the temperature coefficient of resistivity $\displaystyle \alpha$ 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 $\displaystyle 25^{\circ} \mathrm{C}$ and resistance of the semiconductor arm is $\displaystyle 3 \mathrm{~m} \Omega$. Arm BC is cooled at a constant rate of $\displaystyle 2^{\circ} \mathrm{C} / \mathrm{s}$. If the galvanometer G shows no deflection after $\displaystyle 10$ s , then $\displaystyle \alpha$ is :