Fair Test:
As I am only changing the length of the wire, I must keep the following factors the same.
1. The same type of wire, for my first set of readings and my repeat readings. If these are not kept the same, I may get some confusing results.
2. Take readings from exact positions i.e. exactly 6 centimetres along the wire, not 9, as on a repeat this will give odd and confusing results.
Prediction:
If I increase the length of the wire then the resistance will increase.
This happens because if the voltage goes up and the current goes down, according to Ohms law, then the resistance will rise.
Plan:
Method:
Connect circuit as shown in diagram,
Record voltage on a voltmeter,
Record current on an Ammeter,
Repeat the experiment with the same measurements as on the first experiment.
Connect crocodile clips the distance apart shown in my measurements list
Diagram:
Equipment list:
Voltmeter
Ammeter
1 metre of wire
Crocodile clips
Power supply
Connecting Wires
Number of Measurements:
I will take measurements at these 12 places: (in centimetres)
6
12
18
24
30
36
42
48
54
60
66
72
Range of Measurements:
My range of measurements is 66 centimetres - from 6 cm to 72 cm.
Safety:
As with any experiment, there is an element of danger, but I aim to comply with the guidelines set by teachers and not say lick my fingers and connect myself to the power supply, so as not to blow myself up or anyone else for that matter.
Results Queries:
To obtain precise results, I will measure distances to the nearest millimetre and measure result to the nearest 0.1 amp or volt. I will also measure resistance to 2 decimal places. I.e. 5.12345 becomes 5.12
To obtain reliable results I am going to repeat my experiment and I am going to ignore most anomalous results.
Obtaining Evidence:
This is my results table from my 1st experiment.
At the back of this file, there is a graph showing these results.
This is my repeat results table. A graph is shown below.
Analysis:
Anomalous Results:
In my 1st experiment I got 3 results that were a long way off my best-fit line. This may have been because the wire started to warm up and caused more frenzied movement among the current. In my repeat experiment the last 3 results are almost identical. I have no idea why this was.
Conclusion:
Having completed my experiments, the following conclusions can be drawn:
- As predicted, an increase in the length of the wire resulted in an increased resistance.
-
The overall resistances of my 1st experiment and my repeat experiment seem to differ considerably. My 1st experiment only reaches as high as 8.37 ohms of resistance. Whereas on my repeat experiment a figure of 11 ohms was reached. The most likely explanation was that the first wire I used differed in diameter to the second wire I used.
Evaluation:
My biggest mistake as mentioned above was choosing two different wires in two different lessons, as they seemingly differed in diameter, which caused a change in resistance. Wire 1 seems to have given the more accurate results as there are few anomalous results and the results go up in an almost perfect straight line.
Wire 2 has a much more curved line and there are many anomalous results.
Luckily, I had enough reliable and accurate readings to support my conclusion.
If I repeated the experiment I would knowingly test a wire with a wider diameter so that I could prove that the type or wire does have a conclusive impact on resistance of a wire.
