When a steady current flows through a resistor, the resistor heats up. We say that "electrical energy is dissipated" by the resistor, that is, converted into heat. But if energy is dissipated, where did it come from? Did it come from the voltage source through the wires?

Consider an insulating crystal, made up of layers of atoms. what form would you expect the temperature dependence of the phonon heat capacity to approach at extremely low temperatures if the interlayer coupling is i)very strong (rigid coupling), and ii) very weak. explain.