When heat is introduced into a material, the average kinetic energy of the molecules increases. As a result they continually bump each other thereby resulting in an overall increase in volume of the material.
Electrical resistance is the opposition to the flow of current, current is the drifting of electrons when p.d has been applied to the ends of a conductor. Electrical resistance is due to the fact that the moving electrons hit each other and the atoms within the conductor.
I hope i answered that well though!!