An object that conducts electricity poorly at low temperatures.

• A. Semiconductor
• B. Conductor
• C. Insulator
• D. Superconductor

Answer: (A)

The important idea is how temperature affects a material’s ability to conduct electricity, especially in semiconductors. In intrinsic semiconductors, charge carriers come from electrons gaining energy to jump from the valence band to the conduction band. At low temperatures there isn’t enough thermal energy to generate many carriers, so the material acts as a poor conductor with high resistance. As temperature increases, more electrons are thermally excited, boosting conductivity. Metals already have many free electrons, so they remain good conductors even when cooled, and superconductors become essentially perfect conductors only below their critical temperature, not poor ones. Insulators stay poor conductors, but the pronounced drop in conduction with decreasing temperature is characteristic of semiconductors, making this the best fit for a material that conducts poorly at low temperatures.