P2.5 Mains Electricity

Question 1

What’s does DC mean? Give an example

Answer 1

Direct current
Current only flows in one direction
Eg. Batteries

Question 2

What’s does AC mean? Give an example

Answer 2

Alternating current
Current changes direction 50 times every second
Eg. Household electricity

Question 3

What wires are in a plug and what colour are they?

Answer 3

Blue = neutral wire
Green + yellow = earth wire
Brown = live wire

Question 4

What’s a fuse?

Answer 4

A component that has a wire running through it made of a different material/thickness than the rest of the circuit. It’s designed to stop current that is too high flowing through it. Measured in Amps

Question 5

What ratings can fusing have? And what do the ratings mean?

Answer 5

3A, 5A and 13A
There the maximum currents they’d allow through the circuit
If more flows through then the wire heats up and melts meaning the circuit breaks but the appliance is protected

Question 6

Why is there a cable grip on a plug?

Answer 6

To keep all the wires in place

Question 7

Why is there insulation of a plug?

Answer 7

To stop the wires being exposed meaning you can’t get an electric shock - safety

Question 8

What are circuit breakers?

Answer 8

They measure the difference in current in the live and neutral wires. If the difference is too great, an electromagnetic switch opens (trips) which stops the flow of current. They work a lot faster than fuses and can reset easily.

Question 9

How does the earth wire protect the user?

Answer 9

If the live wire touches the case, the current flows through the earth wire (so the case doesn’t become live). The fuse then melts and breaks the circuit.

Question 10

Why don’t some appliances have an earth wire?

Answer 10

Because they are double insulated meaning they have plastic cases so the case can’t become live because plastic doesn’t conduct electricity.

Question 11

What’s the symbol for double insulated appliances?

Answer 11

A square inside another square

Question 12

What are the two equations of calculating power?

Answer 12

Power = energy transferred / time taken

Power = voltage X current

Question 13

What’s power measured in?

Answer 13

Watts

W

Question 14

What’s energy transferred measured in?

Answer 14

Joules J

Question 15

What’s current measured in?

Answer 15

Amps (A)

Question 16

What’s voltage/potential difference measured in?

Answer 16

Volts (V)

Question 17

What’s a period of a wave?

Answer 17

The time it takes to complete one waved measured it seconds

Question 18

What’s the frequency of a wave?

Answer 18

The number of complete waves each second measured in Hertz

Question 19

How do you measure frequency?

Answer 19

1/period

Question 20

How do measure the voltage on an oscilloscope?

Answer 20

The amount of squares from the X axis to the peak

Question 21

How do you measure the period on an oscilloscope?

Answer 21

The amount of squares in a wave times the scale

Question 22

How do you make static electricity?

Answer 22

Friction - if an insulator is rubbed with a cloth it becomes charged by:
Electrons move from the cloth to the insulator and the insulator ends up with an overall negative charge
Electrons move from the insulator to the cloth. The insulator ends up with an overall positive charge

Question 23

How can a balloon demonstrate static charge?

Answer 23

The balloon is charged up by friction and the electrons move to the balloon. When the balloon moves nearer to the wall the negative charges repel and the negative charges on the balloon are attracted to the positive ones on the wall. This attraction makes it stick to the wall.

Question 24

What do we use static electricity for?

Answer 24

Photocopiers and laser printers
Spray painting cars
Filtering factory smoke
Heart defibrillators

Question 25

What are the dangers of static electricity?

Answer 25

A build up of charge can produce sparks which may lead to explosions/fire
Charge builds up when two insulators are rubbed together. This can occur when refuelling aircraft, rolling paper in paper mills and on grain shoots in grain stores.

Question 26

What’s the unit for charge?

Answer 26

Coulombs (C)

Question 27

How is cable thickness and fuse value related?

Answer 27

The thicker the wire, the higher the current so you would need a bigger fuse

Question 28

On a graph would what DC look like?

What would AC look like?

Answer 28

DC would be a straight line

AC would be a curvy line