Mains Electricity
4 marks · NormalA student uses a 230 V electric fan with a power rating of 115 W. The fan's plug contains a fuse, and the outer casing is made of metal.
Calculate the current drawn by the fan to two decimal places.
State the most appropriate size of fuse that should be used in the fan's plug from these options: 3 A, 5 A, 13 A. Explain your answer.
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.
Show answer
(a) 0.50 A
(b) 3 A fuse, because it is just above the working current, but will blow if a large current tries to flow. · must show Selection of 3 A, Reference to protection just above working current
Common mistakes: Incorrect formula rearrangement; Selecting a fuse with a current less than calculated
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Uses correct equation: P = I × V, rearranged to I = P/V
A1 (a) · 1 mark · Correct substitution and final answer (0.5 A), to two decimal places
B1 (b) · 1 mark · Chooses correct fuse: 3 A
B2 (b) · 1 mark · Explains that the fuse value is just above the working current
Worked solution
a) Use so (to two decimal places).
b) The most suitable fuse is 3 A, as it is the lowest value above 0.5 A (the current for normal operation). This will protect the fan, as if a much larger current flows, the fuse will blow and disconnect the circuit.