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An Investigation to Determine the Effect of the Number of Turns around the Core of an Electromagnet on its Strength.

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An Investigation to Determine the Effect of the Number of Turns around the Core of an Electromagnet on its Strength


The aim of this investigation is to determine to what extent, if any, the number of turns on an electromagnet affects its strength.


I predict that as the number of turns around the core increases, its strength will also increase. I believe this because of the laws surrounding the strength of electromagnets. Ampere’s Law below determines the strength (in tesla) of the magnet.


B is in Tesla (10,000 gauss)

‘gap’ is in metres (The opening of the "C ".)

Mu = 4 * pi * 10-7

N is the number of turns in the coil

I is the current in Amps

Because only the number of turns in the coil (N) is variable in this experiment, the strength’s increase should be directly proportional to this value (if there were no turns, N=0, the equation must also = 0). To rearrange this equation:


Preliminary Work

As preliminary work, we experimented with what number of turns and at what voltage we could obtain minimum and maximum measurable results. We discovered that with and iron nail core, the magnetic strength below twenty turns was not high enough to produce measurable results on a discrete scale such as number of paperclips.

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Length of time held in

cup / Petri dish

Type and size of c-core

Gaps between turns

Voltage of power pack

Amount/size of paperclips

Resistance of wire

Size of cup / Petri dish


These are the results gathered during the two experiments, the ‘Increase’ column shows the increase in the average number of paperclips collected since the previous set of tests.

Results collected using and iron nail core

Number of Paperclips picked up



Test 1

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We did find that in some cases, the number of paperclips picked up may have been inaccurate because we could not ensure the paperclips were equally free to move on each test. This meant that on some tests, paperclips were catching on each other in the cup and could not be pulled out by the electromagnet. This could have been solved by using much smaller objects that had a shape so that they did not catch with each other.  Iron filings would have been ideal for the purposes of the experiment, but would have been impractical to use. The large size and weight of the paperclips also meant that very few were picked up with the iron nail at lower number of turns, which would have been solved by using something much smaller also.

In an effort to free more of the paperclips and test the limit of what the electromagnet could carry, we moved the electromagnet in the cup or dish of paperclips. Although this was in the interest of fair testing, by reducing the amount of caught paperclips not being counted, it also introduced another variable, how much the magnet was moved. This was very difficult to do accurately in the short time before we had to turn off the power for each test, and may have produced some unfair results.

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