1. Why does the resistance of a conductor increase with temperature while that of a semi-conductor decreases with temperature?

In a semi-conductor such as silicon, carbon or germanium,
as temperature rises, electrons leave the crystalline arrangement and are set free to
move around. The location they move out from is left with what is called a hole. The
conductance in semiconductors is due to the holes and the free electrons. As the
temperature rises it creates more free electron and holes. This gives semiconductors a
negative temperature coefficient of resistance. In a conductor like a metal the
resistance rises with temperature as the increased vibrations in the atoms impedes the
free movement of electrons.