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Testing the strength of electromagnets

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Testing the strength of electromagnets


     An electromagnet is often a piece of metal in a coil of wire. When the wire has no current flowing through it the core is just a regular piece of metal that posses no magnetic ability. However when the current passes through the wire the core becomes magnetised. This is because the wire has electricity flowing through it and the coils of wire create an invisible electricity field around the core magnetising it- this is an electromagnet.

    Electromagnets are found in computers, telephones and items with electric motors in them.


    My aim is to find the strength of different electromagnets using one of the variables.


    The main possible variables that will alter the strength of the electromagnet are an increase or decrease in the current e.g. 6.0A. Increase or decrease in the amount of coils around the core. Different cores e.g. iron, carbon, copper, wood, steel and air. The weight and the size of the paper clips used. The tighter or looser the coils are. There are also some others- temperature, length of core and its diameter.

Preliminary Experiment

    We carried out a preliminary experiment to see the other factors that could affect the experiment and also to see if we could improve any of the steps in the method. I am going to test between the amps and the coils because I think these will be the easiest variables to do and might get the most range of readings. I have chosen to test 5 coils and 40 coils with 4, 6 and 8 volts because I think this might give me a range of readings. These are our results:

 4 Amps

 6 Amps

 8 Amps

 5 Coils




 40 Coils




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Make safe                                                                                                  I must make sure that I don’t leave the power pack on for too long otherwise the wires and the crocodile clips may become over heated and start to melt. In this experiment we are using a bare electric wire, which could e very dangerous if the voltage is not kept low. As we are using electricity we must be ever cautious of the dangers that it can cause, especially looking out for water, which might be on the lab benches from previous experiments that day which could cause the wires to short circuit.

Range of readings

    I will have a range of readings because I will increase the amount of coils which should increase the amount of paper clips the electromagnet can pick up.


    I predict that the more coils of wire there are the stronger the electromagnet will be because if you increase the amount of coils it should increase the strength of the magnetic field around the core.

The more increase in the current the more electrons there will be passing through the wire which should make the electromagnet stronger.

   The heavier the paper clips the less the electromagnet picks up.

The longer the length of the wire the further the electrons will have to travel along it, increasing the resistance. Because of this the length increase should be proportional to resistance increase. Resistance produces heat, but heat also increases resistance. This is because the atoms in the wire vibrate more due to their increased energy. This causes more collisions with the electrons as the atoms vibrate into the path of the electrons. Resistance is caused by collisions with atoms in the wire.

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reliableone that we got fair result from.


    The trend is that at 5 coils the electromagnet picks up 1 paper clip on an average and as the coils increase by 5 coils each time the number of paper clips picked up increases rapidly and when there are 40 coils the number of paper clips picked up is 243 on an average which means that my prediction was right the more coils there are the more paper clips the electromagnet will pick up therefore the electromagnet gets stronger the more coils there are around the core and of course the length of coil had to become longer as more coils were added. This must be because the more coils around the iron core there are the more current is concentrated to the iron core so the bigger the magnetic field will be causing the electromagnet to pick up more paper clips therefore making it stronger.

     If the wire wasn’t coiling and was just straight a magnetic field wouldn’t as powerful because the magnetic field around a wire is circular and perpendicular to the wire and an easy way to amplify the wire's magnetic field is to coil the wire like this…


(This picture comes from Encarta). A coil of wire like this is often called asolenoid.

So if you coil the wire round an iron bar you will find it has a much larger effect on a compass than not coiling the wire would. However this will only work if current is flowing through the wire.



Exercise Books

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