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GCSE Standard Questions: Electricity in the Home

Q9. The diagram shows a microwave oven.

(a) The microwave oven is connected to the mains electricity supply using a three-core cable and plug. Explain why a three-core cable must be used and not a two-core cable.

As the microwave oven has a metal case there is a danger of electric shock if the appliance is not earthed or couble insulated. The third wire in the cable is the earth wire.

If you just wrote 'to make it safer' that was considered insufficient to get you the mark.

[2 marks]

(b) The microwave oven draws a current of 3.3 amps from the mains electricity supply.

(i) Which one of the above fuses should be used inside the plug?

Explain why you have chosen a fuse of that value.

13A because the fuse rating must be higher than the current drawn from the mains. The other two fuses would 'blow' as soon as 3.3A passed through them.

[2 marks]

(ii) The microwave oven is used to cook a meal.

The microwave oven is switched on for 300 seconds.

During this time 225,000 J of energy are transferred from the mains electricity supply to the oven.

Calculate the power of the microwave oven.

Power = rate of energy transfer

P = E/t

P = 225,000/300 = 750 W

[3 marks]

 

(Total 7 marks)