Q: Define drift velocity.
Answer: Drift velocity is defined as the average velocity with which the free electrons of a conductor move when an external electric field is applied across the conductor.
It is of the order of 10-4 ms-1.
Q: What is Average Relaxation Time (τ)?
Answer: Average Relaxation Time (τ) is the average time that has elapsed since each electron suffered its last collision with the ions/atoms of the conductor.
Q: What is mean free path?
Answer: When an electron moves through a conductor, it suffers multiple collisions with the ions/atoms of the conductor. The average value of the distances covered between two such collisions is called the mean free path of the electron.