MAINS ELECTRICITY
3 marks · NormalA kettle operates at 230 V and is protected by a fuse.
State the correct unit for each of the following: electrical current, electric charge, and electric potential difference.
If the kettle normally draws a current of 8.5 A, which size of fuse should be used: 5 A, 13 A, or 20 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) ampere (A) for current, coulomb (C) for charge, volt (V) for potential difference
(b) 13 A. The correct fuse is just above the operating current but not much higher. 13 A is above 8.5 A but will blow if the current is much higher.
Common mistakes: Choosing a fuse with too low or too high value; Wrong SI units
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States ampere (A) for current, coulomb (C) for charge, volt (V) for potential difference.
B1 (b) · 1 mark · Chooses 13 A fuse.
M1 (b) · 1 mark · Explains the fuse value must be just above working current, not too high.
Worked solution
a) Current: ampere (A), Charge: coulomb (C), Potential difference: volt (V)
b) The working current is 8.5 A. The fuse must be the next size up, so 13 A is used. Using a 20 A fuse gives less protection, and 5 A would blow during proper use.