Electrical power
4 marks · NormalA student is choosing the correct fuse for a 1200 W hairdryer powered by a 240 V mains supply.
Calculate the current drawn by the hairdryer.
Suggest which fuse rating would be suitable: 3 A, 5 A, or 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) 5.0 A · must show I = P/V, Substitutes 1200/240, Includes units
(b) A 5 A fuse is suitable since it is just above the calculated current, so it will blow if there is a fault but not during normal operation. · must show Selects 5 A, Reason: slightly above operating current
Common mistakes: Selecting a fuse much greater than the current for no reason
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Uses correct formula I = P/V.
A1 (a) · 1 mark · Correct substitution and evaluation for I (5.0 A).
B1 (b) · 1 mark · Selects 5 A (not 3 A or 13 A).
M2 (b) · 1 mark · Explains reasoning (fuse rating must be just above normal current).
Worked solution
A 5 A fuse is best, as it is just above the operating current. A 3 A fuse would blow, and 13 A is too high to provide protection.