Module 4 - 4.1.2 Mean Drift Velocity

Question 1

Carrier Density

Answer 1

The number of free charges per cubic metre

Question 2

Mean Drift Velocity

Answer 2

The average displacement per unit time of charge carriers travelling along a wire

Question 3

Compare Drift Speeds with Electricity

Answer 3

Drift Speeds = very slow
Electricity = instantaneous

Question 4

Electron Drift: Normal Temperature

Answer 4

• electrons hurtle around continuously
• collide with ions
• no net energy transfer (due to random movement)
• therefore no current

Question 5

Electron Drift: When Voltage is Applied

Answer 5

• electron accelerated from -ve to +ve
• movement is superimposed on top of random velocities
• responsible for electrical effects

Question 6

Conductors
- n
- increasing temp (4)

Answer 6

Large value for n
Increasing the temperature:
- increases vibrations of the ions
- increases resistivity
- decreases current
- decreases drift speed

Question 7

Insulators
- n

Answer 7

n is near to 0

Question 8

Semiconductors
- n
- increasing temp (2)

Answer 8

n about a million times smaller than conductors
Increasing the temperature:
- increases carrier density
- decreases resistivity (thermistor)

Question 9

Conduction Electrons travel …

Answer 9

faster in semiconductors than in conductors (as n is low)

Question 10

You can alter n (carrier density) by

Answer 10

Adding impurities (doping)