Explanation of Domain Theory
Here we see a close up of the domains, the smallest possible magnets (1/1000th of a mm), which are randomly facing different directions. No current is being applied.
Here the domains are beginning to line up inside the iron core. The amount of current applied is slowly increasing….
…And as it increases, more and more domains become turned, until eventually all have been turned and the magnet is at maximum strength.
Apparatus: Newtonmetre s*
Stand
Clamp
Ammeter
Variable resistor
Mains supply
Electromagnet: Iron core
Wire coil
*I will use two different types of Newtonmetre, one more accurate than the other, used to take readings between 0N and 1N IE the first few results.
Diagram
Method
I intend to measure the strength of the electromagnet by attaching a newtonmeter to a small piece of iron, as above in the diagram. This will then be placed on the top of the iron core, which, when the coil has current passed through it, will become magnetic. This will cause the iron core to attract the piece of iron. I will then pull the newtonmeter upwards attempting to separate the iron pieces and noting down the force needed to separate the iron piece from the electromagnet, in Newtons (N).
I will take a range of 10 readings between 0.5A – 5A, repeating each 5 times to get a fair average result. I will also conduct a preliminary experiment, testing the current range and the number of coils – 1A, 2A, 3A/2A, 4A, 6A, etc. and 120 coils around the core (which hopefully won’t melt).
Graph to show predicted results
Preliminary Experiment
I conducted a preliminary experiment to test different values of current; number of coils and number of readings to be taken to make sure everything was initially safe, and also to make sure the method would provide some suitable and reliable results. The preliminary showed that varying the current by 0.5A each time, between 0.5A and 5A (IE not enough current to melt the plastic wire coating), would be suitable; and that I will keep 120 coils constant as this is a suitable number. I decided that 5 readings of each different current should be taken to give a fair average result.
Obtaining Evidence and Results
Analysing Evidence and Drawing Conclusions
Conclusion
My results clearly show an S curve – although different to my predicted pattern, is still a pattern. There is some distinct proportionality between Current and Force in the middle section ‘B’ because equal changes in Current cause equal changes in the Force required to pull the piece of metal away from the electromagnet. Section ‘A’ shows that the electromagnet takes time to get started before it reaches the start of section ‘B’ (1.5A). Section ‘C’ is where the graph levels off, where the electromagnet reaches maximum strength – there are no domains left to be turned.
Section ‘A’ shows the domains taking time to be turned at first, but once they reach ‘B’ they are more easily turned. Once they get past 4.5A there are barely any domains left. Section ‘A’ is the only part I did not foresee in my prediction.
Scientific Explanation
I put my conclusion down to the Domain Theory, this time different to my initial prediction as I expand on it to explain section ‘A’ on my graph.
To begin with it is quite difficult for the magnetic field to turn the first few domains. After this it is 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 begin to have an affect on the surrounding domains, thus complimenting the larger magnetic field produced by the current. After 4.0A on the graph, the turned domains are now the majority, making it still easier for the remaining few to be turned, thus the levelling off is reached in a curved fashion, rather than a straight change in direction as I predicted.
Domains taking time to be turned Some domains have been turned – affecting remaining domains
The ‘levelling off’ – all domains turned, maximum magnetic strength/force.
The conclusion I drew from my results partially supports my initial prediction, but also partly goes against it. My graph looked similar as the ‘B’ section was the same as the straight line in my predicted outcome graph. However, the appearance of section ‘A’ was not anticipated for. Section ‘C’ basically supports the change of direction in my predicted outcome graph, but then again makes no mention of levelling off.
Evaluating Evidence
Upon looking back at the actual results of my experiment I noticed one flaw in the readings I took – at 2.5A the force was remarkably high, and out of place with the straight line. I avoided this mistake in the conclusion by drawing a “best fit” line, but I must now look into how five consecutive results were so out of place. It can be put down to several changes in the environmental variables of the experiment.
The fact that I took the readings at 2.5A onwards on a different day to the ones before them, I can put the anomalies down to -
or
- Distance between coils and iron core
The number of coils was not altered, it was left as used in the first few readings, however the weather changed somewhat in the course of the gap between the two times of reading taking. Also the distance between coils could have changed as the electromagnet components were left lying on their side, thus changing the exact position of the coils. The results, however fell back into place after the readings at 2.5A, meaning that set of reading are inexplicable and a phenomena.
Maximum accuracy was used when taking readings, as I measured the force required to separate the electromagnet and the piece of soft iron to .01 of a Newton. This ensured pure accuracy throughout my experiment. As it was easy to manipulate the current, taking all readings was simple and no obvious errors occurred during the investigation.
The method I used was agreeable and generally gave pleasing and satisfactory results. My apparatus included an accurate ammeter that measured current to .01 of an Amp, and using my skill I was able to manipulate the variable resistor to my satisfaction, thus I was able to obtain the exact desired current. I am pretty certain that anyone who followed my method would obtain very similar results (excluding the 2.5A readings, for obvious reasons).
The evidence I gathered was generally excellent. When I say generally I mean all except for the readings of 2.5A that read as follows:
These measurements should have fallen in line with the curve of the graph, meaning they should have read at around 1.40N each time to give an average of approximately 1.40 Newtons. They should have looked something like this:
Compared to the rest of the results here, they fit in much better. They are highlighted in bold to show up easier.
I can’t blame the experimental procedure for the flawed results at 2.5A. However, I can hope to improve the method by suggesting a change. This would be that the electromagnet’s temperature be controlled by using a Bunsen burner, and to check that the temperature does not fluctuate at all. I would make another change to the method: to exchange the makeshift electromagnet for a properly built set, which would be more reliable than the one I used. This would eliminate the chance of the distance between coils, and the distance between the core and the coils changing. I think the degree of accuracy I used was fine, and the amount of readings was ideal, as the graph showed even more aspects to the line (or curve) than I had anticipated.
In future I would recommend doing an investigation into the resistance of a copper wire, as I predict this would give similar style results to an investigation into an electromagnet.