Question

What is the drift speed of free electrons?

Answer 1

Recall what happens when electrons under random motion start experiencing a Force due to electric field. The speed at which the shift in the path of electrons happens is called the drift velocity.

Complete step-by-step answer:
We know that the electrons in a metal are not bound to the nucleus and exist as a 'sea' where they are not restricted to have only discrete energy but could have any energy. Thus, electrons in a metal are always in random motion due to the thermal energy that they absorb.

When we apply a voltage across a conductor, all these electrons start experiencing a common force in the same direction. Due to this force, electrons start drifting in a common direction. Though the electrons would continue their random motion, we would see a slight shift in their path. The average of this speed with which an electron shifts its path is called the drift velocity.

Additional information
The drift velocity of electrons in a conductor depends on the number of free electrons present in it and on the average time an electron travels without colliding with another electron. The relation for drift velocity is:
${v_d} = \dfrac{{n{e^2}\tau }}{m}$

Note: Note that the speed with which an electron moves is not the speed of electricity in a wire. An electron need not reach from one end of the wire to the other for current to flow. There are electrons throughout the length of the wire which starts moving as soon as they experience the force. So the speed of electricity is the speed of electric field propagation in that conductor, which is the speed of light in the conductor.