With increase in temperature, the relaxation time ( average time between successive collisions) decreases and hence resistivity increases
OR
In metals there are free electrons at normal temperature so when we increase temperature it resistivity gets increases,so conductivity decreases,while in semiconductor the electrons are not free so when we increase the temperature the covalent bonds begin to break and the electron becomes free so conductivity get increases.
Answers & Comments
With increase in temperature, the relaxation time ( average time between successive collisions) decreases and hence resistivity increases
OR
In metals there are free electrons at normal temperature so when we increase temperature it resistivity gets increases,so conductivity decreases,while in semiconductor the electrons are not free so when we increase the temperature the covalent bonds begin to break and the electron becomes free so conductivity get increases.
In physics, energy is preserved. As resistance takes energy from electrical energy, it will cause the transfer to the heat energy.
As resistance increases, the increase in heat energy will follow.