Answer: (3) the average velocity of a free electron over a large period of time is zero (4) the average of the velocities of all the free electrons at an instant is zero
When the conductor is not subjected to an electric field, each electron moves in a straight line at constant speeds and collides with the lattice ions. The orientation of electrons changes randomly with each collision.
- A random sequence of straight segments is the consequence of any electron’s path over a long period of time, covering many collisions.
- As a result, the average number of electrons passing any small area in any direction is nearly equal.
- So the average electron movement in any direction over a long period of time is also zero. Thus in any direction, the average velocity component is zero.