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Class 12 › Physics › Current Electricity
CBSE2018Class Class 12 · Physics1 Marks · Mcq✅ Verified
Pieces of copper and silicon are initially at room temperature. Both are heated to temperature $T$. The conductivity of
A. both increases
B. both decreases
C. copper increases and silicon decreases
D. copper decreases and silicon increases
✅ Answer & Solution
✅ Correct Answer: D
Copper is a metal: as temperature increases, relaxation time $\tau$ decreases, so conductivity $\sigma$ decreases.
Silicon is a semiconductor: as temperature increases, number of charge carriers $n$ increases, so conductivity increases.
$$\sigma = \frac{ne^2\tau}{m}$$
Hence copper decreases, silicon increases.
