Expected graph
Key factors to vary
I’m going to vary the voltage and current, which are multiplied together to get the power and how many watts are flowing through the circuit.
Key factors to control
The factors I am going to control are the number of coils and the same amount of insulating wire used to wrap around the soft iron core, this will be enough wire for 25 coils. I will use the same amount of iron nails and the same iron core for the whole investigation, I will also use the same wires used to connect the circuit to the power supply which I will also keep the same.
Extent and range of evidence
I am going to use 6 variables; 10, 15, 20, 25, 30, 35 volts. These measurements are recorded off the voltmeter, I will also record the current on the ammeter as I can then multiply the results together and get the power, and I will repeat these 3 times to make my results accurate.
Precision and reliability of evidence
I will make sure that my results are precise and reliable, by making sure that my voltmeter is in parallel and my ammeter is in series. I will be precise when wrapping the coils around the top of the soft iron core and to thoroughly insure that there are 25 coils. I will also make sure that there is the same amount of nails each time and that those are in a pile with the same diameter each time. I will also make my results more accurate by repeating each different power total three times.
Safety
To make sure that my investigation is safe, I will not turn the voltage up too high as this will then rise the temperature of the soft iron core and the insulating wire will begin to burn, this could be dangerous as it also vibrates when hot.
Scientific knowledge
The passage of an electric current along a wire creates a magnetic field around the wire. The fields are in the shape of a series of concentric rings. We can make use of this magnetic field by wrapping a wire carrying a current around a soft iron core. Soft iron is used because it is easily magnetised and demagnetised, so when the power is switched on the magnetic lines of force flow into the iron it becomes a magnet. The more coils of wire used in around the soft iron core, the stronger the magnet is. If there is one coil, and another is added, then the two coils have twice the strength of one. The same as in if the current and voltage is increased going through the coils then the magnet will be stronger.
The shape of the magnetic field is the same as a .
Diagram
Relevant information from trials
From my trials I completed in a previous lesson I found out that the best amount of coils to use is 25 as this gives the electromagnet enough strength to pick up enough nails when the voltage is set to 10 volts and its also not to many coils, so when the voltage is 35 the electromagnet wont get too hot and burn the insulating wire. I found out that the best variables to use were 10-35 volts this means that the electromagnet doesn’t get too hot and 10 volts does pick up a few nails. I also found out that changes the number of coils on the electromagnet wasn’t a good idea as its very difficult to get an accurate reading, so I decided to change the voltage, but as I changed the voltage the current changed on the ammeter, so I decided to have both the current and the voltage change, so I could multiply the answers together to get the power rating in watts.
Changes to Plan
I decided to change my original plan as I wanted to investigate another way of strengthening an electromagnet. I will do this by keeping the power the same and changing the number of coils that surround the soft iron core. To keep the power the same I will set up the exactly the same equipment as before and then set the current and voltage to constant amps and volts. Current being 4.85amps and the voltage being 23 volts, this means the power will be 111.55 watts. I will start the number of coils at 5 and go up to 30 with intervals of 5 and I will repeat these intervals 3 times each and then take an average at the end.
Prediction
I predict that the more coils of wire that are around the soft iron core then more nails will be picked up by the electromagnet this is because, the more coils of wire used in around the soft iron core, the stronger the magnet is. If there is one coil, and another is added, then the two coils have twice the strength of one.
Precision and skill
In my table I found that there were a few anomalous results, so I first drew a graph that represented the results including the anomalous ones and then a graph without them. To make the average of my results accurate I repeated them 3 times and then found the average. The anomalous results are highlighted in the table.
Conclusion supporting prediction
In my prediction I stated that when the number of coils around the soft iron core were increased the more nails the electromagnet will pick up, this means that my prediction was right as my graph shows.
Detailed scientific knowledge
From my graph it also shows that the reason from my prediction was right that when the passage of an electric current along a wire creates a magnetic field around the wire. The fields are in the shape of a series of concentric rings. We can make use of this magnetic field by wrapping a wire carrying a current around a soft iron core. Soft iron is used because it is easily magnetised and demagnetised, so when the power is switched on the magnetic lines of force flow into the iron it becomes a magnet. The more coils of wire used in around the soft iron core, the stronger the magnet is. If there is one coil, and another is added, then the two coils have twice the strength of one.
Evaluation
Quality of evidence and anomalies
I think I had good quality evidence as I had a good range of results and I repeated them 3 times each. Although I did get a couple of anomalous results as shown from the graph, I highlighted these on the table and then ignored them and drew another graph showing a more accurate investigation. Things that could have contributed to these anomalies are; the voltage may have differed throughout the investigation which means that the power would not have been the same, the coils around the soft iron core also may have moved slightly throughout the investigation, similarly the crocodile clips could have been moved when the soft iron core was picked up and then replaced from the plastic beaker. Also the weighting machine might not be completely accurate plus several times I had to use a different weighting machine so I might have got wrong readings. Another reason that I could have collected anomalies in my results might be because I could not be sure whether I had left the soft iron core in the plastic beaker the same amount of time for each different amount of coils and for each repeat.
Suitability of procedure
I think some parts of my procedure was suitable for the time I had to collect my results and to make sure that everything was a fair test and each time I recorded a results I made sure as accurately as I could that it was done in the exactly the same as the one before it.
Changes to improve
If I was to do this investigation again I would change some of the things I did so I wouldn’t get as many anomalies, although I still think I can support my conclusion from my graph because it is scientifically correct but the things I would change would be: I would use the same weighting machine for each test and make sure that it is on an even surface. I would also time the time that I would leave the soft iron core in the plastic beaker of nails, so this would hopefully insure that the investigation would be more of a fair test.
Further work
If I was to extend this piece of coursework I could of carry put the investigation that I was originally going to do, this might help to find out if there are other ways of increase the magnetism of an electromagnet and find out if the results were the same.
