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

Step 1: Look at copper.
Copper is a metal. Cooling it calms the lattice vibrations, so electrons flow more freely and the resistivity drops.

Step 2: Look at silicon.
Silicon is a semiconductor. Cooling it leaves fewer free charge carriers, so the resistivity rises.

Step 3: Combine.
So on cooling, copper's resistivity decreases while silicon's increases. \[ \boxed{\text{decreases in copper, increases in silicon}} \]