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# AQA-PHYA4-1-QP-JUN14 Question 24 Watch

1. Hello,

How did the mark scheme arrive to this solution?

24) A lamp rated at 12 V 60 W is connected to the secondary coil of a step-down transformer and is at full brightness. The primary coil is connected to a supply of 230 V. The transformer is 75% efficient.
What is the current in the primary coil?

Thank you!

-- My working got the answer B for some reason so it must be wrong?

( (60/12)x12 ) / (75%x230) = 0.35A
2. You might be looking at the wrong markscheme - that question is in the 2015 paper
http://filestore.aqa.org.uk/subjects...1-QP-JUN15.PDF
fwiw
power input = (4x60)/3
=80 W

80/230 = 0.347 A
3. (Original post by Joinedup)
You might be looking at the wrong markscheme - that question is in the 2015 paper
http://filestore.aqa.org.uk/subjects...1-QP-JUN15.PDF
fwiw
power input = (4x60)/3
=80 W

80/230 = 0.347 A
You're right I was looking at the 2014 one but doing the 2015 paper! Thanks a tonne for the solution as well !

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