Chapter 8.4 - Mean Drift Velocity

Question 1

Number density definition

Answer 1

Number of free charge carriers per unit volume

Question 2

How are materials classified according to number density

Answer 2

• Conductors - highest number density (≈10^28)
• Semiconductors - middle number density (≈10^17)
• Insulators - lowest number density

Question 3

How do semiconductors carry current

Answer 3

• [Since] Number density is lower

• Electrons must move faster
-Increases temperature

Question 4

New current equation

Answer 4

I = Anev

I - Current

A - cross-sectional area of conductor

n- number density

e - elementary charge (1.60 X 10^-19)

v - mean drift velocity of charge carriers

Question 5

What happens when changing the cross-sectional area

Answer 5

• Mean drift velocity is inversely proportional with cross-sectional area of wire
• Cross sectional area changes. So does mean drift velocity

• Less area = Greater mean drift velocity
-because current must be the same

Question 6

New current equation derivation

Answer 6

• I = Q/t
• number of electrons in given volume is nV
• n = number density
• V = volume

• Charge of number of electrons in given volume is neV
- e = elementary charge

Current = certain volume passing a given point per second
I = V/t
- t = time

Finish the rest at home with notes on laptop