Investigation of factors that affect resistance of a wire

2. Material : The type of material I use will affect the amount of free electrons that are able to flow through the wire. The number of free electrons depends upon the amount of electrons in the outer shell of the atoms, so if there are more or larger atoms with incomplete outer shells then it is likely there'll be more electrons available. If the material has a high number of atoms there will be high number of electrons causing a lower resistance because of the increase in the number of electrons. However if the atoms in the material are close together then the electrons will have more frequent collisions therefore the resistance will increase.

3. Wire length : If the length of a wire is increased then the resistance will also increase. This is because the electrons have to travel a longer distance and so more collisions will occur, because of this resistance is said to be proportional to length.

To choose the variable I am going to investigate I have to consider which would be the easiest, quickest and most accurate.

If I chose to measure the temperature of the wire I would not be able to carry out a fair test because it is extremely difficult to produce and control the range of temperatures needed without the correct equipment.

If I chose to measure the difference in the resistance in different materials although it would be simple to record these results, the graphs that I would draw would after would not show any real connection between the material and the resistance because of the limited number of materials I could test with the equipment available.

The final factor is the length of the wire. To measure and record the findings for this factor would be simple and the results collected could show a connection between the length of the wire and the resistance given by the wire.

From looking at all of the variables I have decided that changing the length of the wire will be the easiest and quickest to obtain results from.

Prediction

I predict that when the length of a wire is increased then the resistance will also increase proportionally. I believe this will happen because the longer the wire the more atoms there are and therefore it is more likely that the electrons will collide with the atoms. So if the length is doubled the resistance should also double, because if the length is doubled the number of atoms will also double resulting in twice the number of collisions slowing the electrons down and therefore increasing the resistance. Hopefully the graph I draw afterwards will show that the length of a wire is proportional to the resistance. If the resistance increases then the current (in amps) should decrease as I increase the length of the wire.

Method

Apparatus:

Power Supply

Ammeter

Voltmeter

Wire

Ruler

Crocodile Clips

Connecting Wires

I will set the above apparatus up as shown in the diagram below. The ammeter and voltmeter I use will both be digital. I have decided to use digital ones because this means the results I collect will be more accurate. If I was to use either an analogue voltmeter or ammeter then my results would not be so accurate as it would depend upon my ability to read off correct results.

Safety

As with all experiments performed, there are a number of safety risks involved. In order to be as safe as possible I will make sure that my experiment is set up correctly and I will be careful when handling my power supply. Although there is no need for safety goggles in this particular experiment, as I will not be using any chemicals or naked flames, I will take the usual precautions regarding my uniform, ie. Tucking my tie in, just to minimise chance of any accidents happening. I will also, obviously, be careful that I do not conduct my experiment anywhere near water as water is a good conductor of electricity.

Fair Test

I will make sure that my test is fair by using the same apparatus each time, by repeating the test for each length three times and then taking an average and by making sure I only change one variable each time. This variable will be the length, I will keep the temperature, thickness of wire and the circuit constant each time.

I have decided that I am going to use a total of 6 different lengths of wire when I collect my results. I have chosen a range of 6 as this will allow me to plot an accurate graph. I will repeat each length 3 times and then take an average. I am going to do this as this will be more accurate and should get rid of any anomalous results.

When I have taken all my readings, I will calculate the resistance of the wire using the equation below.

R = V/I

Results

Below is a results table with the results that I have collected from my experiment.

Wire Length

Current (Amps)

Current Average

Voltage (Volts)

Voltage Average

Resistance (Ohms)

5

0.46

0.45

5

0.58

0.51

0.43

0.42

0.82

5

0.48

0.39

0

0.38

0.69

0

0.40

0.38

0.72

0.69

.82

0

0.37

0.66

5

0.26

0.92

5

0.30

0.28

0.87

0.86

3.07

5

0.28

0.79

20

0.24

0.97

20

0.21

0.23

0.77

0.87

3.11

20

0.24

0.88

25

0.22

.02

25

0.18

0.19

0.84

0.90

4.74

25

0.16

0.83

30

0.19

.07

30

0.16

0.17

.00

0.99

5.82

30

0.16

0.90

From these results I have drawn a graph of the length of the wire and the resistance of the wire. I have taken the resistance, from my average results.

Analysis

From the graph on the previous page I can see that the resistance of the wire is proportional to the length of the wire. This is because the line of best fit goes through, or is very near to all of my points. This shows that if the length of the wire is increased then the resistance of the wire will also increase.

Conclusion

In my prediction I said that when the length of a wire increases than the resistance will also rise in proportion to the length. The graph shows that my prediction was correct, as the line of best fit is a straight line that goes through most of my points proving that the resistance of the wire is proportional to the length of the wire. This also proves that Ohms law which states that the current in a metal conductor, when kept at the same temperature, is proportional to the potential difference.

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.

The resistance of a wire depends upon the number of collisions the electrons have with the atoms of that wire. Therefore, if there are a large number of atoms in a wire then there will be a large number of collisions meaning that the resistance of the wire will increase. If a length of a wire contains a certain number of atoms then when that length is increased the number of atoms will also increase. If the length of the wire was doubled, the amount of atoms are also doubled which in turn means that the amount of collisions double too. This is the scientific evidence I used to back up my prediction which I have now proved to be correct.

Evaluation

From my results table and graph I can see that the results I collected are quite reliable. The line of best fit I have drawn goes through four of my six points. The other two points are also quite close. From looking at the results on my table for these two particular points, I can see that the results for the voltages on them vary by quite a lot, compared to my other results. This could be why they are anomalous. Another possible reason for these anomalistic results is the equipment I used. Although I used a digital ammeter and voltmeter and was careful to use the same apparatus each time, I don't think that the ruler, wire and crocodile clips was a very accurate way of changing the wire length.

If I was to repeat this experiment I think I could improve it in several ways. I would try and find a more accurate way of changing the wire length and I would use different, more varied lengths. As we only had the equipment for a maximum wire length of 30cm I felt our experiments were somewhat lacking in variation. If we had a meter ruler and could have tested 15 cm between each reading as a pose to 5 I feel our results may have been somewhat more valid.

I would also repeat the experiment again with another variable, such as the temperature or width of the wire and then compare the two results or with more than one metal so I could compare the resistance of both.