Question

Why the resistivity decrease as the temperature increase in semiconductor and vise versa in metals?

Answer 1

Semi-conductors are those which conduct electricity partially, due to the availability of few free or conduction  electrons. Semiconductors possess negative temperature coefficient  of resistance. i.e. with increase in temperature, the resistance of semiconductors decreases due to which their conducting nature increases with rise in temperature. Whereas when a metal gets heated, the bondage between molecules and atoms start decreasing and since the metal will expand due to heat the space between the atoms tend to be more. Hence one has to pass through more space in the metal and thereby the resistance increases.

Answer 2

R is inversely related to temperature T so as temperature increases resistance decreases. Specifically, R increases if the T coefficient is pos.(P.T.C) And decreases if T coefficient is neg. (N.T.C) Most conductors have P.T.C and most nsulators have (N.T.C) . xept. like carbon.