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GCSE Level Questions: Magnets and Electromagnets

Q1. The diagram below shows two paper clips hanging from a bar magnet. The paper clips have become magnetised.

 

(a) Label the north and south poles of both paper clips.

Both paperclips have to be labelled correctly to get the mark!

[1 mark]

(b) Sally investigated how the number of turns of wire on an electromagnet affects the strength of the electromagnet.

The diagram above shows the equipment Sally used.

Throughout the investigation she kept the current through the wire constant.

She measured the strength of the electromagnet by counting the number of paper clips the electromagnet could hold.

Explain why it was important that the paper clips were all the same size.

To make it a 'fair test' the paper clips (the number of which is the control variable) need to have the same weight/mass so that the results for different numbers of turns can be fairly compared.

[2 marks]

(c) The table shows Sally's results.

Number of turns of wire on the electromagnet
Number of paper clips held
10
3
20
6
30
9
40
12

 

Describe the pattern of results shown in the table.

As the number of turns increases so does the number of paper clips held by the electromagnet - there is a positive correlation. The number increases in a linear pattern - the number of paperclips is directly proportional to the number of turns on the electromagnet.

[2 marks]

(d) Sally then used 50 turns of wire on the electromagnet.

The electromagnet picked up 18 paper clips.

This was more paper clips than she had expected.

Which one of the reasons listed below is the most likely cause of this result?

Tick one box.

[1 mark]

Reason Tick
The paper clips used with 50 turns were larger than the others.  
There were less than 50 turns of wire on the electromagnet.  
Some of the paper clips were already magnetised.

 

(e) Sally repeated the measurement for 50 turns of wire three more times.

This gave her four readings: 18, 16, 14, 15

Explain what she should now do with the four results for 50 turns of wire.

The result of 18 is not close to the other three - so she should ignore it as an anomaly.
The three new results are similar so she should average them and use 15 as her value (the mean of the new results)

[3 marks]

(f) Sally wrote the hypothesis: 'Increasing the current through the wire will make the electromagnet stronger.'

Describe how she should change her initial investigation to test this new hypothesis.

Sally needs to keep number of turns constant.

Using the variable resistor (rheostat), she should change the current several times and count how many paper clips the electromagnet will hold for each current. She should then repeat her experiment, making sure to demagnetise the paperclips between readings.

[3 marks]

(TOTAL 12 marks)