For our investigation we didn’t use iron filings but we used a soft iron which was the nail, and the wire was wrapped around the core of the soft iron. We used 'soft' iron because soft iron loses its magnetism very quickly when the current stops and normal iron keeps its magnetism when the current stops. The magnetic strength can be increased significantly if the wire is wrapped around the core of the soft iron which forms a coil which is called a solenoid. The magnetic field of each single coil builds up to produce a stronger field around the solenoid. The solenoid behaves as a weak magnet; one side behaves as a north pole and one as a south pole. When current flows through the coil, the iron becomes magnetised. When the current is switched off the magnetic field collapses and the iron becomes demagnetised. This is the principle of an electromagnet. Electromagnets are ‘multi – purpose’ because they are so easily controlled and they are used in places like trains and circuit breakers. The strength of an electromagnet can be varied by: changing the number of coils of wire – the more coils, the stronger the magnet. More wire in one area means that the magnetic field is reinforced by other magnetic fields. A larger magnetic field is created (assuming that the current stays the same), and also by changing the current – the larger the current, the stronger the magnet (assuming the number of coils stays the same). The wire also has to remain the same because different wires could have different resistance. Presuming that the resistance of the wire stays the same then you have to change the voltage to change the current. Current changes in direct proportion to the voltage.
Hypothesis
I hypothesise that the variables that will change the strength of the electromagnet are the number of turns in the coil of wire. I also predict that the increase of current (voltage) will make the electromagnet stronger. The points I have made in my introduction back up my predictions.
To keep the wire variable the same I will use the same wire for each experiment, this keeps the resistant constant. The amount of current (voltage) will be easy to keep the same as you need a key to change the voltage in the power supply I will be using, when we need to change the voltage we will just have to call the teacher over and he will change it because there will be not enough keys to have one per group.
Plan
I am going to test how my variables will influence the strength of the electromagnet. My variables will be amount of turns on the coil and the amount of current. I will use power supply, wire, steel nail, paper with lines marked on keeping 2 mm distance apart and also we need a paper clip. This is how I will carry out my experiment:
- I will get a sheet of plain A4 paper and mark on horizontal lines across the page, 2mm apart. This will act as my ruler when measuring the strength of my electromagnet.
- I will plug in my power supply to the plug and check that it is on the correct voltage.
- I will then coil my wire around my steel nail. Checking that I have used the appropriate amount of turns, for the experiment I will carry out.
- I will connect my electromagnet to my power supply and turn it on so the electromagnet becomes magnetised.
- Before I turn the electromagnet on I will put the nail on a line where it is 0mm to keep it a fair test.
- I will measure how far apart the paper clip will be before being picked up.
Here is a diagram to show how my experiment will be set out
To keep this a fair test I will use the same wire as it will have the same amount of resistance. I will also use the same paperclip as other paperclips could be slightly charged. The same power supply will be used as some power supplies give out different voltage even if the difference is small.
Because my variables will be the same, I can expect my results to be of suitable accuracy. I think that these steps are reliable and anyone, anywhere, anytime can carry this experiment out following my steps and I am confident that they will get similar results but there might be a slight difference because of the equipment is different. I think that the variable which will have the biggest influence on how strong my electromagnet is will be the coils and the number of turns. I predict this because the bigger the range of the magnetic field the more distance the paperclip can be picked from.
Results
