Plan:
In this investigation a simple circuit will be set up to read the voltage and current when the length of the wire changes. The length will range from 10cm - 100cm (1m) with intervals of 10cm.Moving the jockey across the wire on the ruler will change the length of the wire.
The circuit should be set up as in the circuit diagram below. It is important that the voltmeter is set up in parallel and the ammeter in series. The readings from the ammeter and voltmeter will be used to work out the resistance. This can be done using the formula: V=IR (Where V=voltage, I=current and R=resistance.)
To ensure that the investigation is carried out in a fair way and that the results will be accurate and reliable a number of things must be followed. The only variable in the test will be the length of the wire. The wire must be pulled tight against the ruler and taped in place to ensure the length is accurately measured.
The experiment should be repeated 5 times and an average taken to make sure that the results are reliable.
Procedure:
- Set up the apparatus as shown in the diagram above.
- Adjust the variable resistor to allow the smallest possible current to flow in the circuit.
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Note the ammeter reading (I) and the voltmeter reading (V).
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Adjust the variable resistor to allow a larger current to flow in the circuit. Again note the values of I and V.
- Repeat the above at least 5 times and record the readings.
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Plot a graph of V against I.
Results:
The results I found were expected because the results were proportional to each other.
Because the results were proportional it showed that there was a formula possible of getting. The graph shows they were proportional to the best. (Straight positive line, as resistance doubles, so does length).
Conclusion:
In my prediction I said that:
if the length increases than the resistance will also increase in proportion to the length.
From my graph I have shown that my prediction was correct, as the Line of Best Fit is a straight line proving that the resistance of the wire is proportional to the length of the wire. But I have also made some errors, for e.g. I made errors on taking the readings and maybe that is why some of the points don’t fit in the straight line.
The length of the wire affects the resistance of the wire because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases in proportion.
From my results table and graph I can see that my results that I collected are very reliable. I know this because my results table does not show any individual anomalous results this means that I did not have to leave any results out of my averages because they were anomalous. During my experiment I have noticed several modifications I could make to improve on the Investigation if I was to repeat it. The first of these modifications would be the circuit that I would use. To be more accurate with my results I would use the circuit layout below:
Power supply, Voltmeter, Wire, Meter ruler
Instead of connecting the voltmeter to the main circuit I would connect it to the wire, which is being tested. I would do this so that the voltmeter is measuring the voltage of just the wire being tested and not the wires of the main circuit as well.
To also improve on my results I would use a digital voltmeter instead of an analogue meter. I would do this because a digital voltmeter is a lot more accurate than an analogue because if the needle in the analogue voltmeter is bent then the readings given off will be false whereas a digital voltmeter does not rely on a needle or any other manual movements.
The next modification I would make would be to use pointers instead of jockey; I would do this because pointers would be more accurate. The pointers would be more accurate because the tips have a much smaller area than the crocodile clips giving a more accurate measurement of the length of wire.
As well as making these modifications I would also improve my Investigation by testing the same wire but different widths of that wire. I would do this to expand on my Investigation.
