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Strength of an Electromagnet

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Louise King

Strength of an Electromagnet

Aim and Plan


    To find out the strength of an electromagnet by changing the number of coils of wire wrapped around it.


   I predict that as I increase the number of coils around the electromagnet, the electromagnet will be able to lift increasing amount of weight. I predict that when I have plotted out my results into a graph I will have a straight line, meaning that the weight lifted is directly proportional to the number of coils around the electromagnet.


    First of all you will need to set up all the apparatus highlighted in blue on page 2. A diagram of how this should be set up is shown below.

    Now that all the apparatus is correctly set up turn on the power pack and make sure that it is set to 3 volts. Then start with 2 wraps of coil and work your way to 20 from there. Start by slowly adding 100g weights but after that add 10g weights. When the electromagnet can not hold any more the weights will fall and you will have to count up all the weights bar the one that caused the fall and record the weight at the end. Do each experiment at each number of coils three times in total. Then make an average of your results.  


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    I will repeat the procedure three times for each number of coils and then work out an over-all average of my results. This will give me a much more accurate and reliable result. My investigation will be accurate within 10 grams, as 10 grams is the smallest weight that I will use in my experiments. This is quite a high level of accuracy.

Preliminary Work

    Before I carried out my main experiments I carried out some preliminary experiments. I tested to see how many coils I could wrap around the electromagnet so that they were still evenly spaced along it. The most I could accurately get was 50 turns. Below in diagram A is the first layout I tried.

I realised that this did not work because the tin was too weak to support such a large amount of weight. So I used a 100g weight as its shape enabled the hooks to stay more balanced, as shown in diagram B above. This worked well as the 100g weight could support the other weights and wouldn’t fall. I tried other set ups but the one shown in diagram B worked the best.

    I tested 10 turns of the electromagnet with 5 volts from the power pack. It held roughly 700g altogether.

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    Form this graph that it is not a straight, directly proportional line like I expected in my prediction. In fact the results tend to increase exponentially. Therefore my prediction has been proved to be incorrect.


    Some of my results may have been inaccurate due to the iron core being magnetically saturated. This means that the magnetism could not get any stronger. This was probably the case in my experiment as I did the experiments one after another. Although the resistance of the wire would have probably have played some part in it as well. Any resistance in the wire would cause the wire to heat up and would therefore destroy the magnetism.

    If I were to do this experiment again I would try and do it with a wire that had the lowest resistance possible. However I do think that in most respects my experiment was a fair one as far as possible. I made sure that my experiments, in fact my whole investigation was a fair one by setting aside the wire and electromagnet. It was important to use the same wire throughout, as all the wires would have had a varying resistance. The electromagnet would need to stay the same as all electromagnets have varying iron u-core strengths, which would affect my results if varied.

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