Can someone explain to me what potential difference is? simple answers are always better! p. s : last time my electricity question was taken down becuase i put it in teh physics section but i believe it is physics or at least fits physics the best. people answering the question dont mind this.

A47.2 g block of copper whose temperature is 480 k is placed in an insulating box with a 91.8 g block of lead whose temperature is 200 k. (a) what is the equilibrium temperature of the two-block system? (b) what is the change in the internal energy of the two-block system between the initial state and the equilibrium state? (c) what is the change in the entropy of the two-block system? the heat capacities of copper and lead are 386 j/kg·k and 128 j/kg·k, respectively.