2b.1 - Electricity in the Home

Question 1

What voltage is the UK mains supply?

Answer 1

230 V

Question 2

What type of supply is the mains?

Answer 2

AC supply

Question 3

What does AC stand for?

Answer 3

Alternating current

Question 4

What is an alternating current?

Answer 4

The current is constantly changing direction - from positive to negative and back

Question 5

What is the frequency of the AC mains supply?

Answer 5

50Hz

Question 6

What is the unit for frequency?

Answer 6

Hz

Question 7

What does Hz mean?

Answer 7

Cycles per second

Question 8

What type of supply is for batteries?

Answer 8

DC

Question 9

What does DC stand for?

Answer 9

Direct current

Question 10

What is a direct current?

Answer 10

The current always flows in the same direction

Question 11

What does the vertical height on an AC trace show you?

Answer 11

The input voltage - potential difference

Question 12

How do you calculate the voltage for a DC current on an oscilloscope?

Answer 12

The distance from the straight line to the centre line

Question 13

How do you calculate frequency?

Answer 13

1 % time period

Question 14

Name the nine examples of electrical hazards in the home

Answer 14

• Long cables
• Frayed cables
• Cables in contact with something hot or wet
• Water near sockets
• Shoving things into sockets
• Damaged plugs
• Too many plugs in one socket
• Lighting sockets without bulbs
• Appliances without covers

Question 15

What colour is the earth wire?

Answer 15

Yellow and green striped

Question 16

What colour is the neutral wire?

Answer 16

Blue

Question 17

What colour is the live wire?

Answer 17

Brown

Question 18

What is the live wire? (3)

Answer 18

• Brown
• Alternated current - High
• Current flows in

Question 19

What is the neutral wire? (3)

Answer 19

• Blue
• Stays at 0V
• Current flows out

Question 20

What is the earth wire? (3)

Answer 20

• Green and yellow striped
• For safety
• Attached to the metal casing and carries electricity to the earth

Question 21

What wire is screwed to the pin at the top of the plug?

Answer 21

Earth

Question 22

What wire is screwed to the pin at the left of the plug?

Answer 22

Neutral

Question 23

What wires screwed to the pin at the right of the plug?

Answer 23

Live

Question 24

What are the safety features of a plug? (4)

Answer 24

• Right wire in right pin
• No bare wires
• Cable grip
• Thick cables

Question 25

What are the features of a plug? (2)

Answer 25

- Metal parts made from copper or brass because they are good conductors - The case, cable grip, and cable insulation are made of rubber or plastic because good insulators and flexible

Question 26

What prevents electrical overloads?

Answer 26

Earthing and fuses

Question 27

How does the earth wire protect the appliance? (3)

Answer 27

- If live wire touches casing - Too great a current flows in through the live wire - Current flows through the case and down the earth wire

Question 28

How does the fuse protect the appliance? (3)

Answer 28

- Surge in current melts fuse or trips the circuit breaker - This cuts off the live supply and breaks the circuit - This isolates the appliance

Question 29

How should fuses be rated?

Answer 29

Just higher than the normal operating current

Question 30

What is a double insulated appliance? (2)

Answer 30

- An appliance that has a plastic case and no metal parts showing - Doesn't need an earth wire

Question 31

What are the advantage circuit breakers have over fuses?

Answer 31

- A circuit breaker's switch can be closed but you have to buy a new fuse - Faster as doesn't need to wait for fuse to melt - Safer as detects smaller currents

Question 32

What is an disadvantage of circuit breakers over fuses?

Answer 32

Much more expensive

Question 33

Name a type of circuit breaker

Answer 33

RCCB's

Question 34

What does RCCB stand for?

Answer 34

Residual Current Circuit Breaker

Question 35

How does and RCCB work?

Answer 35

Detects the difference in current between the live and neural wire and cuts of power quickly by opening a switch

Question 36

What do all resistors produce when a current flows through them?

Answer 36

Heat

Question 37

What is meant of an efficient appliance?

Answer 37

It wastes less energy

Question 38

A 2.5 kW kettle is on for 5 minutes. Calculate the energy transferred by the kettle in this time. Energy transferred = Power rating x time

Answer 38

2500 x 300 = 750 000 kJ = 750 kJ

Question 39

A hair dryer is rated at 230 V, 1 kW. Find the fuse needed. | Power = Current x Potential difference

Answer 39

1000 % 230 = 4.3 A. The fuse should be higher than normal so a 5 AMP FUSE is used.

Question 40

The motor in an electrical toothbrush is attached to a 3 V battery. If a current of 0.8 A flows through the motor for 3 minutes: a) Calculate the total charge passed b) Calculate the energy transformed by the motor Energy transformed = Charge x Potential difference

Answer 40

a) 0.8 x (3 x 60) = 144 C | b) 144 x 3 = 432 J