Chapter 5 🗽

Question 1

What is the equation for energy transferred from the mains?

Answer 1

Energy transferred from the mains (J)= power x time

Question 2

What is the equation for power supplied (W)?

Answer 2

Power = current x potential difference

Question 3

How do electrical appliances waste energy?

Answer 3

Heating the surroundings

Friction in moving parts

Question 4

Equation for efficiency

Answer 4

Efficiency = output power/input power x 100

Question 5

What is charge flow?

Answer 5

The electrons being forced round a circuit

Question 6

Equation for charge flow

Answer 6

Charge flow (C) = current x time

Question 7

When the charge flows around a circuit for a given time, the envy supplied by the battery is equal to what?

Answer 7

The energy transferred to all the components in a circuit

Question 8

Why does a resistor get hot when charge flows through it?

Answer 8

Energy is transferred to the resistor because the electrons collide with the resistor ions, heating it up

Question 9

What is the equation for power?

Answer 9

Power = energy transferred/time

Question 10

What is the current in an electrical appliance?

Answer 10

The current is the charge that flows through it each second

Question 11

What is the potential difference of an electrical appliance?

Answer 11

The energy that is transferred to the appliance by the charge passing through it

Question 12

Equation for power supplied?

Answer 12

Power supplied = current x potential difference

Question 13

Equation for power using current and resistance

Answer 13

Power = current^2 x resistance

Question 14

What does the earth wire do?

Answer 14

It carries the current into the earth if something goes wrong

Question 15

Why are plugs, sockets and cables made of insulators?

Answer 15

To stop them carrying a current

Question 16

What is the potential difference of the earth wire?

Answer 16

0V

Question 17

Why are the pins made of brass?

Answer 17

Brass is a good conductor and doesn’t rust

Question 18

What does the fuse do?

Answer 18

If the current gets too high, it melts and cuts the live wire off

Question 19

Which is the brown wire?

Answer 19

The live wire

Question 20

Which is the blue wire?

Answer 20

The neutral wire

Question 21

Which is the yellow and green wire?

Answer 21

Earth wire

Question 22

Why is plastic used?

Answer 22

It is a good insulator so you don’t get an electric shock

Question 23

What are two core cables used for?

Answer 23

Appliances with plastic cases

Question 24

Why must some wires be thicker than others?

Answer 24

Carry different currents

Question 25

What happens when a plug short circuits?

Answer 25

The live wire touches the neutral wire

Question 26

Why is copper used in the wires?

Answer 26

It is a good conductor and bends easily

Question 27

What is a direct current?

Answer 27

When the current flows in only one direction

Question 28

What is an alternating current?

Answer 28

When the current repeatedly reverses direction

Question 29

What is frequency in the uk mains?

Answer 29

50Hz

Question 30

What is a step up transformer?

Answer 30

Used to make the size of the potential difference much bigger

Question 31

What is a step down transformer?

Answer 31

Used to supply homes with electricity from the national grid | Takes voltage down to manageable level

Question 32

How do you measure the frequency of an ac supply?

Answer 32

Frequency = 1/ time taken for one cycle

Question 33

what does the live wire do?

Answer 33

carries current to the appliance

Question 34

what does the neutral wire do?

Answer 34

carries current away from the appliance

Question 35

1 kw

Answer 35

1000 w

Question 36

What are the two ways in which efficiency can be expressed

Answer 36

Ratio or percentage

Question 37

Why do electric appliances ways energy because of the wires

Answer 37

The wires have some resistance so the energy is transferred as heat

Question 38

What does a domestic electricity meter measure

Answer 38

How much energy is supplied with

Question 39

What is the energy supplied by the battery equal to

Answer 39

The energy transferred to all components in the circuit

Question 40

How to determine what fuse to use

Answer 40

Use the equation current = power / PD | You use the fuse closest to it

Question 41

What determines whether an appliance should have a 3 or 2 core cable

Answer 41

2 core cables are for appliances with plastic cases

Question 42

Why are some wires thicker than others

Answer 42

Carry more charge

Question 43

What causes a short circuit

Answer 43

When the live wire touches the neutral wire

Question 44

Difference between 2 and 3 core wire

Answer 44

2 core doesn’t have an earth wire

Question 45

What is the PD of electricity in the UK

Answer 45

325 v

Question 46

Why is the PD of the national grid so high?

Answer 46

Much less current is needed to transfer same amount of power

Question 47

What is the live wire in a mains circuit charge like

Answer 47

Alternately positive and negative

Question 48

Which wire is earthed at the local power station?

Answer 48

Neutral

Question 49

What does double insulated mean?

Answer 49

The wires are coated in plastic and the outer case of the appliance is plastic