Why does the resistance of a metal conductor increase with temperature?

• A. Because electrons gain kinetic energy and move faster, reducing collisions.
• B. Because cross-sectional area increases with temperature.
• C. Because the material becomes superconductive.
• D. Because lattice ions vibrate more, making it harder for electrons to move, increasing resistance.

Answer: (D)

The main idea is that resistance in metals comes from collisions of conduction electrons with the vibrating lattice ions. As temperature rises, the ions vibrate more strongly (more phonons). These bigger vibrations cause electrons to scatter more often and more effectively, so their drift under a given electric field is hindered more, and the resistance increases. Thermal expansion of the metal is a smaller secondary effect, while superconductivity does not occur at ordinary temperatures, so it doesn’t apply here.