P17: Household Electricity

Question 1

Direct Current

Answer 1

Electric current in a circuit that is in one direction only.

Question 2

Alternating Current

Answer 2

Electric current in a circuit that repeatedly reverses its direction.

Question 3

What is the mains frequency in the UK?

Answer 3

50Hz (AC)

Question 4

Live wire

Answer 4

The mains wire that has a voltage that alternates between +325 and -325v (in Europe)

Question 5

Neutral Wire

Answer 5

The wire of a mains circuit that is earthed at the local substation so its potential is close to zero.

Question 6

Half wave rectification

Answer 6

The use of a diode in a circuit with an alternating supply pd to allow current in only one direction every other half cycle of the supply pd.

Question 7

Socket

Answer 7

A mains socket is used to connect the mains plug of a mains appliance to the mains circuit.

Question 8

What are plug pins made of?

Answer 8

Brass (Its a good conductor, and it doesn’t rust or oxidise)

Question 9

What is the longest pin of a three-pin plug and why?

Answer 9

The earth plug, because it is the first pin that connects with the wall socket, so the plug is earthed even before the other pins connect.

Question 10

Answer 10

Question 11

Fuse

Answer 11

A fuse contains a thin wire that melts and cuts the current off if too much current passes through it.

Question 12

What does the earth wire protect?

Answer 12

The user

Question 13

What does the fuse protect?

Answer 13

The appliance and the wires of a circuit.

Question 14

Circuit Breaker

Answer 14

An electromagnetic switch that opens and cuts the current off off if too much current passes through it.

Question 15

Why are circuit breakers better than fuses?

Answer 15

They work faster

They can be reset

Question 16

Residual Current Circuit Breaker

(RCCB)

Answer 16

An RCCB cuts off the current in the live wire when it is different from the current in the neutral wire.

More sensitive than fuses/ normal circuit breakers.

Question 17

A fuse is always connected in…

Answer 17

…series.

Question 18

Power Supplied (W) =

Answer 18

Current (A) x Voltage (V)

Question 19

When charge flows through a resistor…

Answer 19

energy is transferred to the resistor, so the resistor becomes hotter.

Question 20

Kilowatt-hour

Answer 20

(kwh)

Electrical energy supplied to a 1kW device in 1 hour.

Question 21

What is a kWh?

Answer 21

A unit of energy

Question 22

Are low power lamps more or less efficient than high power ones?

Answer 22

More, because they give the same amount of light energy for the same input of electrical energy.

Question 23

Filament Bulb

+ and -‘s

Answer 23

very inefficient

heat from the bulb makes the plastic casing go brittle and crack.

Question 24

CFL’s

+ and -‘s

Answer 24

More efficient that filament bulbs

Question 25

LED’s

+ and -‘s

Answer 25

Use a low voltage and low power

V. Efficient

Last much longer.

Question 26

Step Up transformers

Answer 26

raise voltage

lower current

Question 27

Step Down transformers

Answer 27

Lower voltage

Raise current