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The temperature dependence of resistances of Cu and undoped Si in the temperature range 300-400 K, is best described by:

1. Linear increase for Cu, exponential decrease of Si.
2. Linear decrease for Cu, linear decrease for Si.
3. Linear increase for Cu, linear increase for Si.
4. Linear increase for Cu, exponential increase for Si.

Correct answer: Linear increase for Cu, exponential decrease of Si.

Solution

Copper (Cu) is a metal, and its resistance typically increases linearly with temperature due to increased lattice vibrations that scatter electrons. In contrast, undoped silicon (Si) is a semiconductor, and its resistance decreases exponentially with temperature as more charge carriers are thermally excited across the band gap.

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