Question

What is meant by drift speed of free electrons?

Answer 1

Hint: Recall the term drift velocity of the electrons. The drift speed of the electrons is the same physical quantity only in scale form. Explain the process of how the electrons get drifted towards the ends of the conductor and hence define the term drift speed of the electrons.

Complete answer:
In a current carrying conductor, there are always free electrons available at room temperature for the electric current to flow through it. These electrons are not in a steady state. They are always moving with a random speed in any random direction and colliding with its neighbor atoms and electrons. Hence, the et velocity of such electrons is always zero.

But when a potential difference is applied across the two terminals of the current carrying conductor, the electrons being negatively charged starts moving towards the positively charged higher potential terminal of the conductor.

Now the speed of these electrons depends on the applied potential difference across the terminals of the conductor. Though the electrons are moving or drifting towards the positive terminal, they are not moving in a specified path. They still continue their random motion and collision with each other.

When the electron collides with the other electron or atom, it loses a part of the kinetic energy it has and bounces off in the opposite direction. But due to the applied potential, the electron again gets accelerated and starts moving randomly towards the positive terminal.

This process continues until the electrons reach the positive terminal of the conductor.This average speed attained by the electrons by virtue of the applied electric field is called drift speed of the electrons.

Note:The students may assume that each of the electrons moving towards the positive terminal of the conductor has the same drift velocity. But the drift velocity of all these electrons is not the same but is the average of all the velocities of electrons moving towards the positive terminal of the conductor.