Electrons at Work

Question 1

What is a conductor?

Answer 1

A material that allows electrons to move relatively easily (has a low resistance)

Question 2

What is an insulator?

Answer 2

A Material that does not allow electrons to move easily (has a high resistance)

Question 3

What is a semiconductor?

Answer 3

A Material that can act as a conductor or an insulator under certain conditions

Question 4

What are the energy levels like in a conductor atom?

Answer 4

The outer energy level contains electrons but not enough to fill it allowing a degree of movement for the electrons

Question 5

What are the energy levels like in an insulator?

Answer 5

The outer energy level is full and the electrons are fixed or tied in the one level

Question 6

What happens when atoms are brought together?

Answer 6

The outer energy levels form an energy band (the conduction band)

Question 7

What happens in the outer band of a metal?

Answer 7

Electrons can move from atom to atom within the band

Question 8

What is the band level below the conduction band?

Answer 8

The valence band

Question 9

What happens at room temperature in the valence band in semi conductors?

Answer 9

The valence band slightly overlaps with the conduction band allowing electrons to move out to the conduction band and assist conduction

Question 10

Why don’t insulators conduct?

Answer 10

Because the outer level is full so there is no transfer of movement of electrons and charge. This is the valence band meaning the conduction band us empty and without electrons

Question 11

How can you force insulators to conduct?

Answer 11

By providing huge amounts of energy in the form of a large voltage

Question 12

What is the breakdown voltage?

Answer 12

The voltage at which electrons in an unilateral leave the valence bad to jump to the conduction band

Question 13

What happens if you increase the temperature of a semiconductor?

Answer 13

It can conduct more easily

Question 14

What is the band gap like in insulators?

Answer 14

The gap between the valence and conduction band is large and electrons cannot move between them

Question 15

How do thermistors work?

Answer 15

Raising the temperature of a semiconductor increases the number of active charge carriers promoting them to the conduction band so the material can conduct more current

Question 16

What is an ntype semiconductor?

Answer 16

A semiconductor with the addition of an electron making the majority of charge carriers negative

Question 17

How does ntype doping work?

Answer 17

The extra electron means there’s a surplus so can displace electrons in other atoms leading to a chain reaction of moving electrons allowing electricity to flow

Question 18

What is a ptype semiconductor?

Answer 18

When there’s a missing electron in a material leading to the majority of charge carriers to be positive

Question 19

How does ptype doping work?

Answer 19

Due to the missing electron surrounding electrons move in to try and stabilise the atom this leads to more electrons missing as they try to fill the surrounding ‘holes’ allowing electricity to flow (in the opposite direction)

Question 20

What does doping do?

Answer 20

The addition of impurities to produce ntype or ptype semiconductors with increased conductivity

Question 21

What is the depletion layer?

Answer 21

A layer formed by the electrostatic attraction of n-type and p-type semiconductors that have been brought together. Where conduction and valence bands ‘overlap’ in a p-n junction

Question 22

What happens when light is incident on the depletion layer?

Answer 22

Photons can transfer energy to electrons allowing them to move to a higher energy band creating a potential difference and allowing currents to flow. (Photovoltaic effect)

Question 23

How do LEDs work?

Answer 23

When current flows across the depletion layer electrons pass into holes in the layer and move to lower energy levels creating excess energy which is released as a photon

Question 24

What determines the colour of an LED?

Answer 24

The amount of energy released by the electron moving to a lower level. Red light is the lowest frequency so required the least energy