Assertion (A) When a wire of aluminium and another wire of silicon are heated from room temperature to…
Assertion (A) When a wire of aluminium and another wire of silicon are heated from room temperature to $80^{\circ} \mathrm{C}$, the conductivity of aluminium increases and that of silicon decreases.
Reason (R) Aluminium has positive temperature coefficient of resistivity and silicon has negative temperature coefficient of resistivity.
Both (A) and (R) are correct and (R) is the correct explanation of (A).
Both (A) and (R) are correct but (R) is not the correct explanation of (A).
(A) is correct but (R) is not correct.
(A) is not correct but (R) is correct.
Solution
Key Idea In nature, metals have positive
temperature coefficient and semiconductors have negative temperature coefficient.
Aluminium is a metal, so its conductivity decreases with increase in temperature, due to the excessive collision of electron. Whereas, $\mathrm{Si}$ is a semiconductor therefore its conductivity increases with increase in temperature.
All metals have positive temperature coefficient of resistivity and semiconductor has negative temperature coefficient of resistivity. Hence, assertion (A) is incorrect but reason (R) is correct.