We did some tests with different voltages and sizes of wire. We first chose to have the smallest wire we would use as 10cm. We will them increase the size of wire up by 10cm each time until 100cm. We chose that because it is and easy length to use and it can be easily measured.
We then did more test with the 10cm piece of wire to see what would be a suitable length that was not hot. We chose 0.9 volts because a 10cm piece of wire that was the maximum it could be before it started to get hot. We did not want the wire to get hot because it effects it’s resistance and this would then not be a fair test.
Variables: The only variable I will change throughout the experiment is the length of the wire. This is the only input variable.
Diagram:
- Power supply
- 5 Connecting wires
- The test wire
- Voltmeter
- Ammeter
Method:
- Set out the equipment as in the diagram: - Attach one wire from the power supply to the ammeter. - Attach another wire from the ammeter to the test wire. - Put another wire on the end of the test wire back to the power supply - Then place a wire from the test wire to the voltmeter and another wire to from the voltmeter to the other end of the test wire.
- Measure out the length of the test wire to 10cm.
- Turn on the power supply until the 0.9 volts (It is 0.9 volts because that is the maximum voltage before it gets hot) is reached.
- Read the current on the ammeter and record on the chart below.
- Repeat steps 2 – 4, always keeping the voltage 0.9 volts, but changing the lengths of wire: - 20cm - 30cm - 40cm - 50cm - 60cm - 70cm - 80cm - 90cm - 100cm
- Work out the resistance (R) by V divided by I.
I= current V= Voltage = 0.9 volts.
Fair test: These things I must always keep the same to ensure the test is fair and that there is a minimal chance of error as possible:
- Have the same piece of wire each time as different wire could vary slightly or have different properties, so give different results.
- Keep the same voltage throughout the experiment.
- Have the same equipment – wires, voltmeters, ammeters, power supply. – If changed these could give different readings.
- Have the wire measured by the same ruler and person – If someone else does it with a different ruler they could measure it differently or off slightly.
Obtaining Evidence
Results table:
You can see that we repeated some on the tests when we got different answers. We then worked out the resistance (V ÷ I = R) for each test and then calculated the average resistance.
Analysing
Conclusion: I found out that the longer the piece of wire the more resistance created. I know this because my results table shows that as the piece of length wire goes down the resistance goes up. Also my graph shows that as the length of wire decreases the resistance goes up. My graph does not show any anomalies so I know it is very reliable.
- Wire Atom
- Electron
Small piece of Wire: There some atoms in
way of the electrons moving – little resistance
Long piece of wire: There are a lot more wire atoms in the way of electrons – lots of resistance.
Resistance means the difficulty electrons have moving through a material. The resistance goes up because there are more atoms in the way of the electrons, thus meaning that it is quite hard to move through a material with lots of atoms. When there is more atoms in the way of electrons, the electrons are more likely to collide with atoms and then slow down. This is resistance.
I can therefore say that if the wire keeps getting shorter the resistance will keep going down. Also in the other way round – if the wire keeps getting longer the resistance will keep going up. I am quite correct in my prediction where I said that the resistance would go up when the length of wire decreases.
Evaluation
I thought the experiment went quite well because we did everything well and on time and had enough time not to rush. The way was good as we did not receive any anomalies and the results were clear enough to show an answer. There were a few differences in the results e.g. 30cm where we had 0.29 and 0.31 amps. We then repeated these tests to make sure we got the same result as one of the ones before and then worked out the average.
We used the average to plot a graph as this is a good way to show the results and because averages include all results and make it easier to plot.
Also 70cm and 80cm were slightly off, but could still be included by the line of best fit.
The way we did the experiment and procedures was quite good. We turned the power supply off between experiments. We could improve the procedures by increasing the current on longer wires. This wouldn’t affect the resistance as the resistance is worked out by V ÷ I, but would make more accurate and less chance for error. There were also many other things we could improve. When we laid the wire out it wasn’t always straight and sometimes had kinks in it. We tried to straighten it as much as possible and because of this there could have been some errors or mistakes. As the was quite thin there could have been small changes in it’s thickness which would have altered our results. Also the reliability of our equipment and us could have not been good. We may have measured the wire wrong or as the ruler was old and worn away, it was hard to see where the 0cm was and also the numbers could have been rubbed off so we had a wrong measurement. The crocodile clips where also hard to position so could have been place wrong, therefore changing the results. If I did it again I would take these things into consideration and check much more.
I am quite happy with out results because they are good results. The results may have been wrong, but this would be quite unlikely as we have a strong correlation. Also I think that we have enough information to draw conclusions as they show good connection.
Another improvement would also be to change the equipment. It could more precise or have newer ones which wouldn’t have been damaged or altered. Things such as the crocodile clips where hard to position very accurately so I would look for alternatives. The room could have also affected the results. As the day went on it got warmer, so affecting the temperature of the wire. If I wanted to be extremely precise and accurate in future experiments I could do the experiment in a temperature controlled room.
I think the conclusions I have drawn are good. I have strong evidence to base them on and there is good evidence. The errors could have been small mistakes from the equipment. If I did another experiment into this area I would try to do things such as
- The thickness of the wire
- Which type of wire
- The temperature of the wire.