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As the width of the wire increases, the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the electrons, there are less collisions are so less resistance is produced.
I have decided to investigate how the length of the wire alters the resistance as I feel that this experiment will be the most feasible and produce the most accurate results.
This is the circuit that I am going to use to investigate how the resistance of the wire changes as I vary the length of the wire.
The apparatus that I shall need in order to carry out this practical is:
- a power pack
- an ammeter
- resistance wire
- a voltmeter
- crocodile clips
In order to make this a fair test, I will have to make sure that the other three factors are kept monitored and do not alter at any point during the experiment. In order to make sure that the temperature of the wire does not increase at any point, I will use the power pack at 4V to avoid overheating. Also, between readings, the power pack will be switched off. As I shall be using the same resistance wire throughout the whole experiment it is highly unlikely that the width or the composition of the wire is going to change and therefore I do not need to take any measures to ensure this.
When carrying out the experiment, I shall be recording down two readings. The first reading I shall take shall be from the ammeter in order to find out the current. The voltmeter reading will tell me the potential difference. I will take three repeat readings to ensure that my results are accurate. In order to work out the resistance across the wire, I shall work out the resistance for each set of results and then create averages of the resistance. This is the information that I shall plot onto a graph. By using averages from a number of readings, I can ensure that my readings are accurate.
For safety reasons I shall wear and apron and goggles. As I shall be dealing will electricity, I shall need to ensure that all equipment is dry and that no wires are being trailed. Also, by keeping the voltage of the power pack low during the experiment, this reduces any chance of overheating which could then lead to burning or fire.
To work out the resistance in Ohms (Ω) I will use the formula:
Resistance = Current
Voltage
RESULTS:-
These are the results that I got after carrying out my experiment three times:
Using these results I was able to find an average resistance:
I used this information to plot a graph.
ANALYSIS:-
From the graph it is possible to see that as the length of the wire increases, the resistance increases. This is because if the length of the wire is increased then the resistance will also increase as the electrons will have a longer distance to travel and so more collisions will occur.
Although my graph shows that the resistance increase is directly proportional to the increase in the length of wire, I am unable to establish a mathematical link between the two. This is because my results have not turned out as planned. If the results had been correct than the resistance would be approximately one tenth of the length of the wire. However, due to a problem with my equipment, my results only follow this pattern for the first length (10cm).
My results agree with my prediction in that I predicted that as the length of the wire increased, so would the resistance.
EVALUATION:-
I felt that my experiment was not carried out accurately as although the results followed my prediction, they were not the expected results. I think that this was due to the wire overheating whilst taking measurements. However, I feel that my results were as accurate as possible because they formed a smooth curve on the graph and the repeat readings were very similar. I did not receive any anomalous results as all my results fit with my line of best fit.
In order to improve my experiment, I feel that I should measure the length at every 5cm to receive more points on the graph to be sure of its shape. Also, a wider range of readings could be taken, perhaps up to 150cm; to see if a t any point the graph would start to level off. In addition, I would take steps to reduce overheating of equipment as this tends to distort results.
From my investigation, I can conclude that as the length of the wire increases, the resistance increases. This is supported by the smooth curve on my graph and the similarity in my repeat readings.
