Fair test
To keep this experiment fair we must only change one variable-the cross sectional area. I must keep the amount of power equal. I must keep the length of wire the same and must use the same material each time. To make the results more accurate I must do each surface area three times and then calculate the averages.
Safety
Be careful because the wire might get very hot due to friction. Take care when setting up the circuit to make sure that I don’t set up the circuit wrong to short circuit it.
Method
I will get a roll of wire and cut of ten lengths each of 35 centimetres. I actually want it 30 centimetres but I have to allow for wire to be allow the crocodile clips to connect. So some wire will not be included so I have left five centimetres. I will connect this wire to the circuit using crocodile clips and then I will turn the power on and record the readings of the ammeter and voltmeter and write these values and work out the amount of resistance taking place. The power pack will be kept the same throughout the whole experiment to keep it fair.
Trial run
I will set up our circuit like the diagram below
A=Ammeter
V=Voltmetre
In my trial run I started of with my circuit and when I was about to record he volts and amps the wire get extremely hot and started to smoke. After this occurred I thought I should add a variable resistor to help overcome this problem, and it worked.
So I decided on a new circuit
=Variable resistor
Results
1st lot of results
2nd
3rd
Conclusion
Resistance is caused by the internal structure of the metal getting in the way of moving electrons. Metals conduct electricity because the atoms in them do not hold on to their electrons very well, and free electrons, carrying a negative charge jump over atoms in a wire. Resistance is caused when these electrons flowing towards the positive end have to jump atoms. The more difficult it is for the electrons to move the higher the resistance. So the larger the cross sectional area the larger the space for the electrons to move about in meaning not a lot will be getting in the way of the moving electrons.
It is the cross-sectional area of the wire, not its thickness, which directly affects its resistance. The cross-sectional area is what you get if you cut straight through the wire,
at right angles to its length, and look at the cut surface If the wire is round then the cross-section is a flat circle and the area is πr2.
We see that if the area of the wire doubles, so does the number of possible routes for the current to flow down, so resistance might halve, So saying this if you doubled the area the resistance will be a halved.
Evaluation
Problems I had
Most errors in my experiment were encountered in the measuring of the wire. This is because it simply was not very practical to hold a piece of wire straight, whilst holding it next to a ruler and then trying to accurately fix crocodile clips to the right part on the wire. Also I do not feel that the crocodile clips were always fixed securely to the wire with a good connection. Crocodile clips have a spring in the to keep them shut and this could have compressed the wire therefore increasing the resistance. When I was in the middle of recording my results the ammeter and voltmeter where very slow in telling me the results, and after looking at my circuit I thought this was probably due to a lose connection somewhere in the circuit, so I lost quite a lot of time trying to find out what was making the lose connection, but eventually I found out it was due to the wire.
Quality and Anomalies
I think the quality of the results collected was quite good as most of the results fitted my best-fit line. As you can see on the graph I have ringed two points which seem slightly wrong, as they aren’t really part of the curve.
As you can see on the graph I have ringed two points which seem slightly wrong as they aren’t really part of the curve.
Reliability
I think my investigation was quite reliable but when I put the wire in the circuit by the crocodile clips I didn’t always measure the wire inside the crocodile clips so this probably made a difference to the results. Also when we kept adding the wires I didn’t realize for a while that it would be better to twist the wires around each other so sometimes the wires made not have been connected aswell as they could have been. So if I did the experiment again I would make sure the wires we all twisted round each other and that I measured the wire each time.
Further investigating
If I wanted to find out more about resistance I could try the other factors that affect it,
1) Type of wire- This would tell me whether the material of the wire affects the amount of resistance or not.
2) Length of wire- This would tell me if the resistance is more in a shorter length of wire or a longer one.
This way I would gain a better knowledge of resistance.
By Paula Takle
