Current causes the temperature of a real resistor to increase why? What effect does thisheating have on the resistance? Explain

The basis of this effect is kinetic molecular theory -
which means that the particles in all matter are always in motion as long as the
temperature is above absolute zero. Their rate of motion is directly related to the
temperature of the material.

So in a copper wire the atoms
are constantly interacting and vibrating. When a current is passed through the wire it,
in a sense, has  to force its way through the material in the wire. This results in
internal friction which then produces heat. The heat, in turn, causes the particles to
move even faster, producing more heat and more
resistance.

So the higher the temperature of a material,
the more resistance the material has.

This phenomenon also
is at work in high voltage transmission lines. Much of the energy produced at the power
plant is lost as the current flows through the lines to the end
users.

Engineers have proposed cooling these lines to
relatively low temperatures to decrease the resistance of the current in the lines.  If
the temperature is reduced enough, to the critical temperature of the material, the
resistance disappears and the material becomes a superconductor. Much research is being
done to find alloys whose critical temperature is relatively high so not as much energy
is needed to cool them down.