Consider the following two statements. (A) Free-electron density is...

Peltier effect is the evolution or absorption of heat at the junction of two different metals when an electric current is passed through it.

This effect arises because different metals possess different free-electron densities (Statement A). When electrons cross the junction from one metal to another, their average energy changes due to the difference in electron densities, resulting in the absorption or release of heat.

Since the Peltier effect occurs at a junction that can initially be at a uniform temperature, it does not depend on the temperature variation of the free-electron density (Statement B).

Therefore, the Peltier effect is caused due to A but not due to B.