Question 1

There are three wires in a UK plug. Which statement is true about the earth wire?

Accepted Answer

It only carries current if there is a fault and the live wire touches the metal casing.

Answer

It has the fuse connected to it.

Answer

It is a blue wire.

Answer

It is at a potential difference of 230 V with respect to the neutral wire.

Question 2

What are the pins in a mains plug made of?

Accepted Answer

brass

Answer

copper

Answer

magnesium

Answer

plastic

Question 3

Which is the correct statement about fuses?

Accepted Answer

If the fuse ‘blows’ the current in the circuit will stop flowing.

Answer

If the live wire touches the neutral wire a long circuit is created.

Answer

A fuse is designed to melt if the current is too low.

Answer

The fuse is in the earth wire.

Question 4

Which is the correct charge based on the current and time values below?

Accepted Answer

A current of 10 mA flowing for 20 s means that the charge flow is 0.2 C.

Answer

A current of 150 mA flowing for 10 hours means that the charge flow is 1500 C.

Answer

A current of 1.5 A flowing for 1 minute means that the charge flow is 1.5 C.

Answer

A current of 3 A flowing for 10 s means that the charge flow is 0.3 C.

Question 5

Choose the correct definitions of direct and alternating current from the statements below.

Accepted Answer

Mains electricity provides an alternating current which reverses direction, but batteries provide a direct current, which only flows one way.

Answer

Mains electricity provides an alternating current which only flows one way, but batteries provide a direct current which reverses direction.

Answer

Mains electricity provides a direct current which only flows one way, but batteries provide an alternating current which reverses direction.

Answer

Mains electricity provides a direct current which reverses direction, but batteries provide an alternating current, which only flows one way.

Question 6

Which statement about power is correct?

Accepted Answer

The power of a travel kettle labelled '24 V, 5 A' is 120 W. If it heats water for 15 minutes then 108 000 J of energy are transferred.

Answer

The power of a light bulb labelled ’12 V, 2 A’ is 6 W. If the light bulb is switched on for 5 hours then 430 kJ of energy are transferred.

Answer

Potential difference is the power transferred per unit charge, and the current is the charge that flows per second.

Answer

A powerful appliance transfers less energy per second, so a more powerful lamp is dimmer than a less powerful one.

Question 7

Which appliance needs a 5 A fuse?

Accepted Answer

750 W microwave oven connected to the mains supply of 230 V a.c.

Answer

10 W phone charger connected to a 230 V a.c. mains supply

Answer

15 W PlayStation connected to a 230 V a.c. mains supply

Answer

1500 W hairdryer

Question 8

Which statement is correct?

Accepted Answer

An oven is 75% efficient. If the power input is 3200 W you would get 2400 W of useful power out.

Answer

An LED torch is 85% efficient. For every 200 W of input power there will be 170 W lost to the surroundings as thermal energy.

Answer

A radio that produce 50 W of useful power for every 75 W put in has an efficiency of 125.

Answer

If the power input is 2000 W for an electric motor that is 50% efficient, then the power output would be 40 W.

Question 9

Select the correct statement about kWh below.

Accepted Answer

An electricity meter measures energy transfer in kilowatt hours

Answer

To work out the energy that has been transferred in kWh, you multiply the power in watts by the time in hours

Answer

1 joule is much bigger than 1 kilowatt hour

Answer

1 joule = 3600000 kWh

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