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To investigate the effect of current on the strength of an electromagnet field.

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Physics Sc1



To investigate the effect of current on the strength of an electromagnet field.

Previous Scientific Knowledge.

The passage of an electric current along a wire creates a magnetic field around the wire. The fields are in the shape of a series of concentric rings. The more coils used in the electromagnet, the stronger the magnet is. If there is one coil, and another is added, then the two coils have twice the strength of one. This is because the current going through the wire makes the soft-iron core is the factor that induces electromagnetism, as so when there is more current, there will be more wire or or a more magnetised core.

Magnets were formed when certain molten metals, (iron, nickel and cobalt,) cool . Normally when the atoms in a non magnetic crystallise, the atoms point in random directions. But because of the properties of the metals mentioned, these atoms line up into parts of the magnetic with similar directions called domains. This is because the earth has a magnetic field, and the atoms in the metal all follow these magnetic lines and form these domains. This is similar to what happens when an electromagnet is formed.

A permanent magnet will line itself up in the magnetic field of the Earth, so that one particular end of it points towards the Earth’s magnetic north pole. This is called the north-seeking pole of the magnet and the other end is the south seeking pole.

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The quantity that I am intending to investigate in my experiment is the strength of the electromagnet. The factors that affect the strength of an electromagnet are: The temperature, current, length of the core, diameter, the thickness of the wire used for the coils, how tightly the coils of wire are wrapped around, the material and also the number of turns on the electromagnet. I am only going to vary current in the experiment, all the other factors I will keep constant. I have chosen to vary current because, the more turns there are, the more powerful the magnet becomes and therefore the more domains there are. The thicker the diameter is, the more domains there are in the middle and therefore the stronger the electromagnet becomes. The higher the temperature is, the easier it is for the domains to be able to turn and line up. If you use a thinner wire it will cause more resistance in the experiment. All of these factors will change the strength of the electromagnet.

I decided to do current, as the others were more difficult to do. I believe that when I do the experiment, proportionally as the current increases, the strength will increase.


1) A 2.5 m electrical wire will be coiled around a soft-iron core 100 times.

2) Crocodile clips will be connected to yellow connecting wires at each end.

3) These together with the ammeter will be connected up to the power supply as shown in the circuit diagram.


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  • Number of coils of wire around the electromagnet.
  • Type of material acting as the core e.g. iron, steel.

I think that the  experiment was done successfully as all the repeats were similar, and we did not have any anomalous points, as shown on the graph. These could have been the result of human error in noting the readings of current or the weight of the cup, however this is unlikely as two sets of repeats were carried out

The reliability of the results could have been improved by;

  • A more accurate ammeter could have been used which measured to 2 decimal places instead of one.
  • A wider range of current readings and a stronger electromagnet could be used to ensure that saturation was achieved, this would improve the reliability of the results and support the original prediction more accurately.

To ensure that the point of saturation is reached I would like to repeat the investigation perhaps with more coils around the electromagnet. This would increase the current and in turn strengthen the electromagnet’s field pattern, resulting in more domains being lined up and saturation occurring earlier.

I would also investigate using different ferromagnetic materials acting as the core, I know that the softer the metal is the easier it is for the domains to be lined up. The electrons of each atom in a metal produce a resultant magnetic field because they are moving charges and moving charges form electric currents. These resultant magnetic fields would vary depending on the type of metal and so it is important I experiment with different metals acting as a core. Saturation could also be achieved earlier by increasing the strength of the electromagnet.

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