Unit 3

Question 1

Define the Valence Band

Answer 1

The highest energy band where electrons normally reside

Question 2

Define Conduction Band

Answer 2

The energy band abige the valence band

Question 3

In a conductor, what is happening with thr valence and conduction bands

Answer 3

They overlap which means that electrons can move freely between the bands and through the material so electrons can flow and the materials conduct electricity.

Question 4

In an insulator, what is hapoening in terms of the valence and conduction bands
?

Answer 4

The Valence and Conduction band are seperated by a large ‘band gap’.

Question 5

In a semi-conductor, what is happening with the valence and conduction bands

Answer 5

There is a small band gap

Question 6

What impact does doping have?

Answer 6

Improves performance by lowering resistance

Question 7

How does doping work?

Answer 7

Adds charge carriers which lowers resistance

Question 8

How do you work out vPeak from an Osciloscope Practical Experiment

Answer 8

(Distance between X axis and top of wave) x yGain

Question 9

How do you work out Frequency in a oscilloscope experiment

Answer 9

T = (how many boxes wide one wave is)x TimeBase

Question 10

What is the definition of alternating current

Answer 10

Where the current changes directions many times per second

Question 11

What is meant by an e.m.f of 9V?

Answer 11

9 Joules of energy are given to each coulomb of charge that passes through the cell.

Question 12

How do you calculate the internal resistance when you have access to a graph with V(E.M.F) plotted against I(Short Circuit)

Answer 12

Get the -gradient of the straight line

Question 13

What is a capacitor

Answer 13

A capacitor is a device which stores electrical charge.
The amount of charge it can store is dependent on its capacitance (measured in farads) and the voltage to which it is charged.

Question 14

Complete the following:

Silicon and other semi-conductors can be doped to form ….

Answer 14

P-type and n-type semi-conductors

Question 15

Describe LED Theory

Answer 15

Electrons fall from conduction band of n-type to valence band of p-type. This results in the emission of a photon.

Question 16

Using band theory, explain why conduction can take place in a semiconductor at room temperature.

Answer 16

The bandgap between the valence and conduction bands is small.

Some electrons have enough energy to move from the valence to the conduction band.

Question 17

A potential difference is produced when photons enter the layer between the p-type and n-type materials. State the name of this effect.

Answer 17

Photovoltaic Effect

Question 18

What is the formula for lost volts

Answer 18

Ir

Question 19

List all the formulas for electricity etc

Answer 19

E = V + Ir 
E = IR + Ir
E= V + Vlost
E = IR + Vlost
V = IR
Vlost = Ir
E = I(R + r)

Question 20

What is meant by capacitance

Answer 20

The charge stored per unit of potential difference