# Design of a variable resistor

1. We found out that the thicker the copper wire it has less resistance, and thinner the copper wire it has more resistance. We also found out that shorter the wire it has less resistance, and longer the copper wire it has more resistance. We found out that the thinnest copper wire, which has diameter of mm has average resistance of 0.06174412, the medium thickness copper wire, which has the diameter of mm has average resistance of 0.

059712123, and the thickest wire, which has diameter of mm has average resistance of 0.05657483. We also found out that the difference in average resistance between mm and mm is 0.002031997, and the difference in average resistance between mm and mm is 0.003137293Therefore, our hypothesis for resistance of copper wires with different diameters did not fit.

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We wrote that larger the diameter of copper wire, it will have more resistance because copper wire generally has higher resistance and since it is largest, it will have more resistance. However, it was opposite. Larger the diameter of copper wire, it had less resistance. We found out that the shortest copper wire which is 10cm, has average resistance of 0.

053542026, the medium length wire which is 15 cm has average resistance of 0.06549226, and the longest length which is 20 cm wire has average resistance of 0.067887666We also found out that the difference between the average resistances of 10 cm and 15 cm is 0.011950234, and the difference between the average resistances of 15cm and 20cm is 0.002395406 The results of resistance of copper wires with different lengths fit in with our hypothesis. Longer the wire it had more resistance and shorter the wire, it had less resistance. From our results, I now think that the wire with2. I think our data is reliable, since there is not any numbers (results) that does not seem to fit in to other results.

We also repeated our experiment three times, and when we repeated, the numbers did not change much. Our data tell us that this is the right conclusion, because when we repeated, the numbers (resistances) did not change much. If all the numbers for the same wires were very different, it might mean that our data is not correct. However, the numbers for the same wires were not very different when we repeated the experiments. Therefore, I think our data is reliable.We looked at the ammeter and volt meter carefully, from the same angle every time we recorded the results.

If we had looked the ammeter or volt meter from different angles, our results might have been different since it looks different depends on where you look at it from. We looked it straight. 3. There is not any pattern. I only found out that the difference in average resistance between mm and mm is 0.002031997, and the difference in average resistance between mm and mm is 0.

003137293, and the difference between the average resistances of 10 cm and 15 cm is 0.011950234, and the difference between the average resistances of 15cm and 20cm is 0.0023954064. There is not any result that does not fit into the pattern. It is hard to know this because we only had three different types of copper wires for each experiment.

5. Our results fit in with what I know already from everyday life. I knew that wires generally had resistance. First, we thought that thinner the wire, less resistance, and thicker the wire, higher resistance.

However, after I looked at my results, I noticed that it was wrong. I now know that the thinner the wire, it has higher resistance and thicker the wire, it has less resistance, because thicker the wire, there is more space for electricity to travel. Thickness would not make the electricity travel slower. It creates more space for electricity to travel, so, more electricity can travel through the wire in the same speed.The results for the wires with different lengths also fit into what I already know from everyday life. As I said, I knew that wire generally has resistance.

Longer the wire, the electricity has to travel more resistant wire, and shorter the wire, the electricity has to travel shorter distance.  Evaluation 1. I think that the methods we have used are reliable. I think they are reliable because we repeated the experiment three times, and we kept things the same, that we had to keep the same.

We wrote down controlled variables, dependent variables, and included in our methods. During the experiments, we did not have any problem. If our methods were not reliable, there have had been some problems.2. There was not any anomalous result. 3. The scientific problem we had was that because the current and volt of the electricity was small, it was hard to read the numbers. Also, the differences between different lengths/diameters were quite small that we had to be very careful when we read the numbers.

I think it had been better if there was an electric ammeter and volt meter. Or ammeter/volt meter with bigger spaces between each numbers.4. To improve our methods, we could have used longer wires (for the diameter experiment) to see bigger differences. For the lengths experiment, we could have used three different lengths with more difference. (e.g.

15, 30, 45), also to see larger differences. We also can use ammeter and volt meter with bigger space between each numbers. 5. I think the first suggested improvement, which is to change the lengths of the wires would make more differences in resistances between the three wires. The second suggested improvement, which is to use bigger ammeter/volt meter (ones with bigger space between each numbers) will make the results clearer. It will give the accurate results since it is easier to see.

6. To follow up this investigation, I can now do an experiment with different types of wires (e.g. copper, lead, nickel, etc) to test which type has the highest resistance and which has the lowest.

7. This will be useful. Variable resistors are important since it is used in many places such as in science lab and in household electrical equipments. If we know the resistance of each types of wires, we will know how long or big (thickness) of the wire is suitable for the replacement of the variable resistors.

If we know the resistance of different types of wires, we can also find the cost-effective way to make variable resistors.