I think this will happen because the tighter coiling of the wire may obstruct the flow of the current and lessen the magnets strength. Having a large amount of turns may also have a negative affect on the iron’s molecular magnets; (atoms in a small range of metals that produce magnetism) they may become aligned differently and in a sense ‘confused’ causing them to be less efficient. The effect I think this could produce is that the molecular magnets would be told to align in different places so that they would be aligned incorrectly, thus making the magnet weaker.
For these reasons I believe that long, spread out turns should produce greater strength, (as long as they cover the whole area) because they are simpler and therefore align the molecular magnets in a more natural and ordered manner that avoids confusion.
Plan
To carry out the experiment I will create a series circuit in which an electromagnet can be set up with a varying number of turns in its coil. From this I will measure its strength by testing how much weight it can hold suspended magnetically.
Variables
The factor that I need to query is whether to keep the size of the turns the same. This sends up to possibilities: firstly that the turns are not all the same, but the same amount of wire is used in the coil each time, or that they’re all the same meaning that the coils length varies with the number that there are.
I have chosen to use the latter method because I think the changing the size of the turns would have a greater negative effect than changing the length of the coil.
Please understand that by this I mean the length of wire that becomes the coil, rather than the entire wire, as it was already a certainty that its overall length should remain constant.
The factors that I will keep the same are:
- The length of the wire with the coil in it
- The size of the turns in the coil
- The voltage from the lab pack
- The current as measured at the ammeter
- The factor that I’m going to change is the number of turns in the coil.
Safety Precautions
There are many obvious safety precautions to be taken:
- Do not allow any water near the experiment
- Do not touch any bare wire while there is a current passing through the wire
- Do not plug lab pack into a socket, which is on
- Certainly do not touch the pins of the plug while it is connected to the live mains supply
- Make sure that the magnet isn’t suspended too high; so that when the weights fall they don’t damage anything
- Also be sure that no one will be harmed when the weights drop; by falling on hands for example
- Do not exceed a current of 5 amps or wires will begin to melt
Preliminary Experiment
I carried out a preliminary experiment to test whether my system for the experiment would work.
This experiment used a fairly long piece of thin wire, which was stripped at both ends with a wire stripper. This became the coil, which was put around an iron nail that was to be the core. The lab pack that provided the power for the experiment was plugged in at the mains and set to 8 volts. A series circuit was constructed which contained an ammeter, variable resistor and the electromagnet.
One of the main purposes of this preliminary experiment was to find a suitable means of gathering the results. There were many different ways to test the magnets strength open to me. These included: seeing how many iron bars it could pick-up, how many iron shavings, how many paper clips, how many paper clips in a line, how far it could pull some iron or how many weights it could hold.
It occurred to me that the smaller objects would make more precise measurements and if they were unsuitably small the test could become less accurate. I thought that iron shavings would be too fiddly and I didn’t like the idea of using paper clips either. I thought that iron bars may have been good, but it turned out that they were all different sizes and so couldn’t have been used fairly. It was through this that I came about using weights for the experiments. These were to be piled on a hook, which was suspended from an iron bar that was stuck to the electromagnet.
It was also decided at this time to use a horseshoe shaped magnet rather than a nail or a bar. This was because they have both poles bent to the same end and is therefore more efficient with strength. This magnet was held in a clamp above the table so that there was enough room for the weights to be held underneath it.
The experiment didn’t turn out very well and I was delayed somewhat because I thought I had used a faulty lab pack. The fault however, lay in my set-up as I had taken the power from the alternating current where a magnetic experiment of this type requires a direct current supply.
Following this I was able to start and though my results were puzzling, I now knew how to set up my experiment and get the magnet working.
I now believe that these puzzling results (the weight held going up and down) are due to the variable resistor being altered so that the amount of current was changed. I’m not sure how it was altered but I will now be extra careful about it in my experiment. I have also decided to use a much smaller current of one amp in my experiment so that it is easier to measure (it was complicated to use so many weights). So far these have been some interesting results as although flawed they are conflicting with my predictions to say that the strength of the magnet goes up with the number of turns in the coil.
Method
Starting the main experiment, I set up my equipment as shown in my diagram. The power pack was activated; set to a D.C supply of 8 volts. This was connected to the ammeter, which displays the current that was altered using the variable resistor until it was approximately 1 Amp.
Through a series of connection wires and crocodile clips the ammeter was joined to metre long piece of wire that was stripped at both ends. This was twisted around the horseshoe shaped iron as the coil, repeated with the relevant number of turns each time. The coil then linked to the variable resistor, which came back to the lab pack, completing the circuit.
During testing the magnet was suspended with a clamp, an iron bar stuck to the poles (once the current is flowing) and a hook to hold weights suspended from that. For each increasing number of turns the hook was loaded with 10g weights until it couldn’t hold anymore.
Unfortunately this is an experiment in which human error could play a large part. Because of this I always made sure to measure the final weight twice, to make sure that this was the point when it definitely could not anymore and that it wasn’t just an accident.
On the next day the experiment was repeated and average results taken. This was to make the results more accurate, in case the first tests were biased for some reason.
Equipment Used:
Circuit Diagram
This diagram shows the layout of the circuit using the universally recognised symbols. The horseshoe shape represents the electromagnet and the opening represents the D.C power supply.
Analysis
My results definitely show that the number of coils has a positive affect on the magnets strength. The graphs show this very well as they have very clear positive correlation. The graph also resembles the graph for current through a resistor, demonstrating the direct influence that the number of turns has.
It’s also noticeable that the second reading was more effective; this must have been caused by there being a greater current on this occasion, probably due to the position of the variable resistor. This could also have been because a different metal bar was used each time. However the difference was only about 10g per reading
One thing that I find odd about the first graph is the way the lines wiggle as they go up. This is because the amount of grams held makes big jumps. Therefore if the increments I used were smaller, perhaps ascending in 5’s rather than 10’s the graph would have been a lot straighter.
For this reason I plotted the average reading graph and used a trend or ‘best fit’ line. This demonstrates the results that I would’ve had with a better degree of accuracy and less bias.
Conclusion
There is now no doubt as to whether I was wrong and that the turns do have a positive effect on the strength of the magnet. I have learnt that it’s possible for smaller, imprecise to be more efficient. I realise now that I was ignorant of this when drawing up my hypothesis. To be more specific, I didn’t realise how small a molecular structure is and that the molecular magnets will benefit from having very small, numerous turns, as they themselves are so very small.
In essence, the smaller and more precise the turns of wire are, the more accurate and precise the molecular magnets will be aligned. The better aligned they are the closer the magnet comes to becoming a completely magnetised and are thus more powerful.
Evaluation
I would not say that my results are particularly accurate but they are however correct. This I know because they are definitive and I understand how this happens. The problem lies in the degree of accuracy, which I believe to be quite poor (despite giving the right result). If I were to repeat the experiment I would use much smaller objects thus improving the accuracy.
It would have also been enlightening to carry on the experiment to see if there is a point where the magnet cannot become any stronger as it is fully magnetised. Some people suggested that a negative effect might kick in but this would not happen, the magnet would simply stop getting any stronger because the molecular magnets are fully aligned.
Nevertheless my results are definitive enough and so I am pleased with my findings.