Compare — 5 marks
A household has two different types of electrical appliances: a kettle rated at 3000 W and a bedside lamp rated at 40 W. Both are connected to the same 230 V domestic mains supply. The homeowner is concerned about electrical safety and wants to understand how these appliances differ in their electrical characteristics.
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(a) Compare the current drawn by the kettle and the lamp when each is operating normally.
[2 marks]
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(b) Explain why the kettle requires a thicker cable than the lamp, referring to your answer to part (a).
[2 marks]
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(c) Both appliances have a fuse fitted. Suggest why a 13 A fuse would be appropriate for the kettle but a 3 A fuse would be appropriate for the lamp.
[1 mark]
Show mark scheme
- (a) Kettle draws a larger current than the lamp (1 mark)
- (a) Kettle current ≈ 13 A and lamp current ≈ 0.17 A (or correct use of I = P/V for both) (1 mark)
- (b) Larger current in the kettle causes greater heating effect in the cable (1 mark)
- (b) Thicker cable has lower resistance, so reduces heat generated / prevents overheating / reduces fire risk (1 mark)
- (c) The fuse rating should match the normal operating current of the appliance to provide protection without nuisance tripping (1 mark)
Show — 3 marks
A family is reviewing the electrical safety features in their kitchen. They notice their kettle has a three-pin plug with a fuse rated at 13 A, and they want to understand why this safety device is important for protecting their appliance and home.
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(a) Show that a kettle with a power rating of 2600 W operating at 230 V would require a fuse rated at approximately 11 A.
[2 marks]
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(b) Explain why a 13 A fuse is appropriate for protecting this kettle rather than a 3 A fuse.
[1 mark]
Show mark scheme
- (a) Uses correct formula: I = P ÷ V or I = P/V (1 mark)
- (a) Correct substitution and calculation: I = 2600 ÷ 230 = 11.3 A ≈ 11 A (1 mark)
- (b) A 3 A fuse would blow/break the circuit during normal operation as the current (11 A) exceeds the fuse rating, preventing the kettle from working / A 13 A fuse allows normal operation but still provides protection if a fault occurs (1 mark)
Calculate — 2 marks
A student uses a 2 kW electric kettle connected to the 230 V mains supply to boil water.
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(a) Calculate the current drawn by the kettle.
[1 mark]
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(b) The kettle takes 3 minutes to boil the water. Calculate the energy transferred by the kettle.
[1 mark]
Show mark scheme
- (a) 8.7 A (accept 8.69 A or 8.695 A)
- (b) 360 000 J (accept 360 kJ)
Explain — 3 marks
A student is using a kettle to boil water. The kettle has a metal case and is connected to the mains supply using a three-core cable containing live, neutral, and earth wires. The kettle is fitted with a fuse in the plug.
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(a) Explain why the fuse is connected to the live wire in the plug.
[1 mark]
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(b) Explain how the earth wire and fuse together protect a person from electric shock if the live wire inside the kettle becomes loose and touches the metal case.
[2 marks]
Show mark scheme
- (a) to break the circuit and stop current flowing (into the appliance) / to disconnect the appliance from the high voltage
- (b) a large current flows (to earth through the earth wire)
- (b) this causes the fuse to melt / blow / break
- (b) this breaks the circuit / stops current flowing / isolates the appliance
Describe — 2 marks
A washing machine is connected to the mains electricity supply using a three-pin plug with a fuse.
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(a) Describe the function of the fuse in the plug.
[1 mark]
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(b) Describe what happens to the fuse when the current becomes larger than the fuse rating.
[1 mark]
Show mark scheme
- (a) prevents a large current flowing (which could cause fire or damage to the appliance)
- (b) the wire in the fuse melts and breaks the circuit (stopping the current)
GCSE Perfect