Module 4 - Charge and current (Mean Drift Velocity)

Question 1

What is meant by the mean drift velocity

Answer 1

The average displacement of electrons along a wire per unit time

Question 2

Why is the mean drift velocity taken as an average

Answer 2

The electrons are often moving randomly in all directions

Question 3

What is meant by the number density of a material

Answer 3

The number of free charge carries per unit volume

Question 4

What is the equation for number density

Answer 4

n = n(free charge carriers)/v

Question 5

What is the relationship between number density and electric conductivity

Answer 5

The higher the number density the better the conductor

Question 6

What is the order of number density of conductors

Answer 6

28

Question 7

What is the order of number density of semi-conductors

Answer 7

17

Question 8

What is the order of number density of insulators

Answer 8

Negligible

Question 9

Derive the equation I=Anev

Answer 9

For any given wire you have the length and the cross-sectional area: A, l
Volume = Axl
Number density = num of free chargers per unit volume (Al)
num of free Charge carriers = Q/e
num density (n) = (Q/e)/Al
Q =Alen , Q= It
It = Alen
I = Aen x l/t
I = Aenv
I= Anev