Question

Silicon and copper are cooled from 300 K to 100 K, the specific resistance (resistivity)

• A. increases in both copper and silicon
• B. decreases in both copper and silicon
• C. decreases in copper and increases in silicon
• D. increases in copper and decreases in silicon

Hint:

Always remember their opposite temperature behaviors: Conductors become better at conducting when cold (resistivity $\downarrow$), while Semiconductors freeze out their charge carriers and turn into insulators when cold (resistivity $\uparrow$)!

Answer 1

The Correct Option is C

The variation of electrical resistivity (specific resistance) with temperature depends fundamentally on the type of material: * **Copper (Conductor):** In metallic conductors, cooling slows down thermal lattice vibrations, reducing electron collisions. This causes the resistivity of a conductor to **decrease** when cooled. * **Silicon (Semiconductor):** In semiconductors, the number of charge carriers available for conduction drops exponentially as temperature drops because fewer electrons can cross the energy gap. This causes the resistivity of a semiconductor to **increase** when cooled. Therefore, cooling the materials from 300 K to 100 K decreases the resistivity of copper while increasing the resistivity of silicon.
Final Answer:
The resistivity decreases in copper and increases in silicon, matching option (C).