Electricity
6 marks · NormalA lamp is connected to the mains supply in a household circuit. The lamp has a power rating of 60 W and operates at 240 V.
State the SI units for power, voltage, and current.
Calculate the current flowing through the lamp when it is operating at its rated power.
Explain how the use of a fuse in the plug protects the lamp and the user if a fault occurs.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) power: watt (W), voltage: volt (V), current: ampere (A)
(b) 0.25 A
(c) A fuse melts when too much current flows; this breaks the circuit and prevents overheating or electric shock, protecting both the lamp and the user.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct SI unit for power (Watt) given.
B2 (a) · 1 mark · Correct SI units for voltage (Volt) and current (Ampere) given.
M1 (b) · 1 mark · Correctly uses P = I × V with rearrangement for I = P/V.
A1 (b) · 1 mark · Correct calculation of current (0.25 A). (follow-through)
B3 (c) · 1 mark · States that the fuse melts or breaks the circuit when excess current flows.
B4 (c) · 1 mark · Explains how this protects the lamp/user from overheating or shock.
Worked solution
a. Power: watt (W), voltage: volt (V), current: ampere (A).
b. Rearranging gives: I = P / V = 60 / 240 = 0.25 A
c. If a fault causes too much current, the fuse melts. This opens the circuit and stops the current, preventing the lamp from overheating or causing electric shock to the user.