Connector wires- To connect the power pack to the coiling wire.
Paper clips- Paper clips are magnetic so they are a good method to test the strength of an electromagnet.
Soft Iron bar- I am using this is our core because it is the strongest core. Materials that could also be used as cores include Steel, nickel, aluminum and cobalt but these become permanent and are therefore useless in an electromagnet because they would have become permanent magnets so are therefore useless to use more than once without demagnetizing them. The soft iron core is useful when you want an electromagnet to switch off rapidly incase it gets too hot.
Diagram
Fair test
To make sure that this experiment is conducted as fairly as possible I have come up with a number of things that need to be kept constant. The reason I need to keep conditions on the experiment as regular as possible is so that I can get accurate results and graph, otherwise there is little point of conducting the experiment.
The voltage, all the apparatus and measuring equipment all must be kept the same. I need to make sure that every variable remains the same apart from the amount of coils because I will need to change this to give me my range of readings.
For each individual experiment I am going to make sure that the current is the same, by checking the ammeter and adjusting the dial accordingly, because the voltage is known to vary as the experiments go on. Only one factor (i.e. coils) will be changed.
Resistance is affected by heat, and the increase in resistance should increase the heat. So I will make sure that I let the apparatus cool down for about a minute in between each individual experiment. The heat causes the atoms in the wire to vibrate quicker causing higher resistance.
I must also make sure that the size of each paper clip is roughly the same because the bigger the paper clip the heavier it tends 2 be and heavier the paper clip the stronger the electromagnet will have to be to pick it up. I will also make sure that the paper clips aren’t balancing on the electromagnet because this means that the electromagnet isn’t attracting the paper clips.
I must keep the coils evenly spaced and tight because from my preliminary test I found that the tighter the coils the more paper clips were picked up. I am also going to test to see if any paper clips are picked up if I don’t have any coils of wire around my iron core.
I must also use the same size and weight iron core because iron is the best core to use and the same piece of wire is used.
Measurements I will write down how many paper clips are picked up from 0-40 coils going up in fives. So at 5 coils then 10 coils then 15 coils and so on. I am going to repeat the test 3 times to see if there are any anomalies against the other results and the anomalies that I might find I will not average out. I have also decided to keep the voltage to 4 volts. This is because it is a fairly low voltage and is quite safe, bearing in mind there are bare wires in this experiment. Also I have chosen this low voltage because it means from the findings of my preliminary tests I can raise or lower the voltage if need be.
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.
Prediction
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. So the more you increase the temperature the weaker the current will be.
The strongest core to use should be soft iron.
The thicker the diameter is, the more domains there are in the middle and therefore the stronger the electromagnet becomes. It is thought that all magnetic materials are made up of tiny groups of atoms called “domains” (0.01 to 1.0mm in diameter), each of which is like a mini-magnet with its own North and South Pole. In any Iron bar there are many of these domains. When the bar is unmagnetized, the domains are randomly oriented canceling out any magnetic effect like this:
Using the current in the coils, you would be able to re-align some of the
domains. If you did this and as a result more of the domains were pointing
in the same direction, then the iron would have become a weak magnet and magnetism is produced.
A weak magnet would look like this:
The iron bar should lose its magnetism almost instantly after it is no longer in contact with the electric current in the solenoid is switched off.
When you switch off the current, the domains would return back to a random set up. Obviously, if you were to line more domains up, the magnet would become much stronger, until you were to reach a state where you had aligned all the possible domains up.
A fully magnetized magnet would look like this:
The tighter the coils around the core the stronger the electromagnet will be because it should concentrate the magnetic field to a smaller area making it stronger. If the coils are wound tightly into a compact circle, not spread out in a long coil. For a long coil the strength is proportional to the current and the number of turns per unit length (e.g. number of turns per cm) in the coil. The strength is proportional to the number of turns per cm, not the number of turns. So if you have a long coil, and keep making it longer with extra turns, it doesn't get any stronger. If the turns are spread out, it should start to change from being a compact circular shape to a long coil. So the more compact the coils are the stronger the magnetic field should be. The bigger the core the less paper clips it will pick up because the wire has to magnetize more area to make it strong.
To begin with it will be quite difficult for the magnetic field to turn the first few domains. After this it should be easier for the domains to be turned because the more domains that are turned, the easier it is for others to be turned. After the initial few have taken time to be fully turned, they should begin to have an affect on the surrounding domains this should will increase the size of the magnetic field increasing the strength of the electromagnet itself.
Results table
The results in bold are anomalous because they do not fit in with the pattern that the other results follow. I didn’t average them out because it wouldn’t be a fair test if I did because they must have been a flaw in those experiments.
The graph has seemed to pick up a trend- the more coils there were the more paper clips the electromagnet would pick up.
Evaluation
There were 4 anomalies occurring in the 1st test (the ones in bold on the table). I think these occurred because the power pack we were using wasn’t as strong as the one we used for the other 2 tests because we used two different sets of equipment. The other reason that some of the results were anomalous was because the voltage used wasn't precisely accurate as the dials on the Power Packs can be misread slightly. To improve the test I could have done another test from 20-35 coils because I got odd readings/anomalies on those ones in test one so couldn’t average them up which could have given me a more fair average result.
To improve the test we could have done more tests using different variables for example if I did a different experiment where I used a different variable i.e. increasing the voltage the diagram would be the same as my original one. I would start form 2 volts and then 4 colts then 6 volts but I wouldn’t go up to 8 volts because in my preliminary test it showed that the circuit was broken because the equipment got too over heated. I would have probably found that the more current is flowing through the circuit the stronger the electromagnet would be because the more current there is flowing through the coiling wire creating a bigger magnetic field so the more paper clips are picked up.
To improve the test I could have also measured each length of the wire because as more coils were added the length of the wire had to get longer and the length of the wire could have been one of the variables, using Iron filings or something that would give a more accurate weight, using a material for a core which won't become a permanent magnet when the electricity is turned off and taking more readings at increased amount of coils (more than 40 coils) to try and get to the point of magnetic saturation.
I could have also done another test from 20-35 coils because I got odd readings/anomalies on those ones in test one so couldn’t average them up which could have given me a more fair average result.
The experiment may not have also been a completely fair test, as the iron bar would attract about 1-2 paper clips when the electricity was turned off. This meant that the nail did become slightly magnetized but only by a small amount.
The electromagnet was still increasing the amount of paper clips it was picking up when I reached 40 coils which means that the Magnetic Saturation point (i.e. where the electromagnet reaches maximum strength – there are no domains left to be turned) hadn’t been reached yet so I could have gone further adding more coils to get a better range of readings the trend line would eventually level off into a continuous straight line.
I think that my results are 7/10 reliable because there were only a few anomalies and the anomalies that there were I didn’t include in my graph. Although I could have used the same equipment so I made sure that I was using the same power pack, length of wire and iron bar and so on it was a fair test. So all in all I could have maybe done with a bit more time to cover more of the variables of the strength of an electromagnet but the variable on coils I did cover was reliable one that we got fair result from.
Conclusion
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 a solenoid.
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.
References
Encarta
Exercise Books
