Question

Assertion $\left(A\right)$: A piece of copper and other of germanium are cooled from room temperature to $100\text{K}$. Conductivity of copper increases and that of germanium decreases.
Reason $\left(R\right)$: Copper has positive temperature coefficient where as germamium has negative temperature coefficient.

Study both the statements carefully and then
Select your answers, according to the codes given below

• A. Both $A$ and $R$ are true and $R$ is the correct explanation of $A$.
• B. Both $A$ and $R$ are true and $R$ is not the correct explanation of $A$
• C. $A$ is true and $R$ is false
• D. $A$ is false and $R$ is true

Answer 1

The correct option is A Both $A$ and $R$ are true and $R$ is the correct explanation of $A$.

Variation of resistivity with temperature is
$\rho ={\rho }_0(1+\alpha \Delta T)$
As copper is a conductor and germanium is a semi-conductor, copper has positive temperature coefficient where as germamium has negative temperature coefficient.
So, when cooled resistivity of copper decreases, while its conductivity increases.
Similarly, when cooled resistivity of germanium increases, while its conductivity decreases.