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Electromagnetism - investigating what effect increasing the number of turns in a coil on an electromagnet will have on the strength of the electromagnet.

Extracts from this document...

Introduction

Physics Coursework

Rebecca Newiss 10O2

Introduction

        In this investigation I aim to find out what effect increasing the number of turns in a coil on an electromagnet will have on the strength of the electromagnet, and the weight it is capable of holding.  I predict that the higher the number of turns there is on the core the higher the amount of weight the magnet will hold.  Also I predict that, if I double the amount of turns in the coil on the core, the magnetic field strength of the electromagnet will also double, I will find out if this is true from the weight it is capable of holding.

E.g.)   20 turns will hold 50 grams

          40 turns I predict will therefore hold 100 grams

        Above is a predicted example of what I think might happen when I increase the numbers of turns in a coil on an electromagnet.  I do not know that twenty turns will hold fifty grams, as this is just an estimated amount.

Theory

        In a piece of iron there are millions of tiny ‘atomic magnets’, they are called this because in each atomic magnet there is a North and a South Pole.  In the piece of iron these tiny atomic magnets line up with each other in small groups, when they do this they become domains.  In a piece of iron, that is unmagnetised, the domains will all point in different directions, see diagram 1 below, the domains are shown by small arrows, the arrowhead indicates the North Pole.  As all the domains are pointing in different directions there will be no true north seeking or south-seeking pole in the piece of iron as the domains will cancel each other out, therefore the piece of iron will remain unmagnetised.

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Middle

  • Then I will record this weight in a table.
  • Then I will release the core from the clamp and wrap ten more turns around the core, I must keep the ammeter reading 3A at all times.  Again I will hang weights off the nail, and record the total weight that the magnet is capable of holding.
  • I will carry on adding ten turns to the coil until I have 100 turns in the coil, every time I get a result I will record it in my table.
  • To achieve accurate and reliable results I will repeat the whole experiment twice again so I will have obtained three results for each number of coils on the electromagnet.

Variables

        These are the only factors that I will be changing throughout my experiment, the factors I will keep the same I have stated in my fair test.  The only changes that I will be making to the experiment is the number of coils on the core, I will do this by taking the electromagnet out of the clamps and wrapping ten more turns on to it, and then replacing it.  I will also have to change the weight that I put on the electromagnet; I will have to keep adding ten grams until the nail falls off the magnet.  I will do this because it will find the strength of the electromagnet.

Range

        As I am only finding out what effect the number of coils has on an electromagnet, I will not be changing the current that I use, therefore I will keep this at 3A at all times.  I found out this range from my pretest, I wanted to go up in 10s so there is a large enough difference between results and not too large difference, as I don’t want the magnet to become fully magnetized too soon.  In my opinion nine results is enough to plot a good graph and to find a general pattern.  I didn’t start at 10 turns as this didn’t hold any weights, I didn’t want to go any more than 100 as I found the coil was getting too hot and could burn out.  The range that I will be using for my experiment is:

NUMBER OF TURNS

20

30

40

50

60

70

80

90

100

Fair Test

        In my experiment I will keep these variables the same in order to keep my experiment fair.  If I changed any one of these factors throughout my experiment I would find that it changes my results and the experiment is no longer a fair test.

  • I will use the same piece of wire to create the turns in the coil so that the thickness and length will not change.  If either of these factors was to change there may be an increase in resistance this could decrease the strength of the electromagnet, therefore a weaker magnet is produced.
  • I will use the same nail because different nails might be attracted to magnets easier than other nails.  A rusty nail will not be as attracted as a clean, shiny one would be.
  • I will use the same u-shaped core in my experiment so that the size does not change.  A large core would take loner to magnetize than a small one and might also hold more than a small core; therefore we would get different and unfair results.  I will use an iron core because this magnetizes and demagnetizes quickly, whereas steel takes time and would not give me accurate results.
  • I will have to use the same method of measuring the magnetic force of the magnet I have decided to use ten-gram weights because weights would give me an answer in grams straight away; a Newton meter would give an answer in Newton’s.  This is not a problem as I could easily use a conversion graph to convert my results; although with a Newton meter you must read off the strength very quickly and can easily been mistaken therefore I will use weights in my experiment, as it is more reliable.
  • I will keep the current the same as I am only testing to find the effect the number of coils has on an electromagnet.  The current must not be too low as the results would be inaccurate but not too high as it might trip the power pack and burn out the wire.  I will use 3A; I found this from my pretest results.
  • I will try to keep the coil of wire at the same temperature throughout, as I do not want the wire to burn and melt its plastic coating, as this is dangerous.  I will do this by allowing a cool down period where I will turn off the current and leave it for a few minutes.  It will be impossible for me to keep the temperature exactly the same at all times but I feel that the temperature will not affect my results greatly.
  • Another important factor I will keep the same is the method I put the weights on the electromagnet, if I put them all on gently instead of dropping them on I will find that my results will be much more accurate.  I will also I will also add ten gram weights not 100, as ten grams is much more precise.
  • I must also try to keep the area that the turns on the electromagnet at the same size throughout, by doing this it will ensure that the concentration of magnetic fields stays the same.  I need to do this as more concentrated turns will provide more strength to the electromagnet.
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Conclusion

        I could also change the method in which I measured the strength of the electromagnet; instead of using ten-gram weights I could use drawing pins or paper clips. These both would give me an exact weight that the electromagnet was capable of holding.  I could use a compass instead of weights, I would move the compass nearer and a slow speed toward the electromagnet, I would record the distance from the electromagnet the compass was when it was affected.  This method would not be suitable for my experiment, as it would not conclude my aim.  

        To investigate further I would see what affect thicker wires, yet the same amount of current, had on he electromagnet.  I feel that there possibly would be no affect but I might be wrong, therefore I should find out.  I will also investigate the concentration of the wires, I think I will find that the smaller the concentration, the area the wires cover on the soft iron core, the more powerful the electromagnet will prove to be.  I will do this by investigating with the area the wires cover on the core; I will then test the results I gain three times each and record then.  I shall look for any obvious patterns.

Rebecca Newiss

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