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GCSE Level Questions: Transformers

Q1.

(a) The diagram shows the basic structure of a step-up transformer.

(i) What is the core made of?

The core made of (laminated soft) iron

It cannot be steel - as steel is a hard magnetic material. You got the mark for iron - but really should know that it needs to be 'soft' and 'laminated' too!

(1 mark)

(ii) Explain how an alternating input produces an alternating output.

An alternating current in the primary coil produces a magnetic field/flux which is alternating / changing /varying. This induces an alternating / changing potential difference across the secondary coil by electromagnetic induction.

(3 marks)

(b) Fly killers are used in kitchens and food stores because flying insects carry diseases which cause food poisoning. The diagram on the right shows the inside of one design.

Insects are attracted to a fluorescent lamp. The metal grids have a high potential difference (p.d.) between them. The insects are killed as they fly between the grids.

A transformer is used in the fly killer. The coil has 300 turns of wire on the primary coil and 4000 turns on the secondary coil. There is a p.d. of 230 V across the primary coil.

Calculate the p.d. across the secondary coil in volts.

 

Vs = NsVp/Np

= 4000 x 230/300

= 3067 V

allow all 3 marks for 3060 V to 3070 V

This is an example of how at A level you would be expected to quote an answer that would not get you a mark at GCSE!

The values in the calculation are given to 2sf - therefore the answer should be finally quoted to 2sf (3100 V). However if you do this your answer would not be within the range they award full marks for.

Hopefully your paper would be marked by someone who knew what you were doing... 'hopefully'.

Therefore always show all stages of your working.

(3 marks)

(TOTAL 7 marks)