Why does a paramagnetic substance display greater magnetisation for .the same magnetising field when cooled. How does a diamagnetic substance respondto similar temperature changes?

When water is heated at its boiling point or melting point, its temperature does not change. Why is there no change in temperature?

When potential difference is applied between the ends of conductor the electrons will flow through the conductor with a constant average velocity. A potential ‘V’ Is applied across a conductor of length l . Keeping the potential difference same, the length of the conductor is halved. How does the velocity of electrons change?