今次係electricity問題....

Upon the action of an applied electric field, electrons in a conducting wire accelerate and pick up speed. But there are collisions between the accelerated electrons and the atoms of the wire. Kinetic energy from the electrons is then transferred to the atoms and make them vibrate more virgorously. Since vigorous vibration of atoms contributes to heat, this is the reason why electric current can heat up the conducting wire.

After collision with the atoms, electrons lose their kinetic energy and slow down. The applied electric field then accelerates the electrons, and the whole process is repeated again.

Thus, electrons in the wire is undergoing repeated acceleration, collision, and acceleration... and so on and so forth.

In the equation: i = naqv
v is the mean drift velocity. It represents the average velocity of the "acceleration-collision" process of the electrons.