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# Resistance of a wire.

Extracts from this document...

Introduction

Resistance of a wire coursework

Resistance of a wire

Planning

Aim:

In this investigation I am trying to find out how the resistance of a nichrome wire changes when current and voltage is changed. I will find this out by measuring the current at different intervals. I will only have one variable, which will change to make this experiment fair.

Variables:

Thickness, length, material (nichrome wire), voltage, current and temperature.

Fair testing:

For any of the above I will only change one variable at a time. I have decided that I will use length as my variable, because it is the easiest to change. With thickness  I would have to measure the diameter  and because it is a very fine wire that will be very difficult. If I use material then it would have to be a metal or I wont be able to check the resistance, also there are loads of different materials so I cant test all of them. Finally with temperature I would find that difficult because the temperature of the room may affect the temperature of the wire, so I would have to keep the wire in a constant temperature, which is not possible unless it is put in a controlled temperature room. So the best possible variable would be the length

To make it a fair test I also have to control all the other variables-

Thickness, Material, Length and Temperature:

Thickness :

To control the thickness (cross sectional area) I will use the same piece of wire. This thickness of the wire can be determined by the amount of space their was in between the atoms. If a wire has

Middle

When taking down my reading, I set them out on a table displaying all the relevant results.

I carried out the experiment three times to make sure the results were accurate. I then found an average from all three sets of results. Below is the table with the results gained.

 Length (cm) Voltage (V) Current (A)
 1st 2nd 3rd 1st 2nd 3rd 20 0.76 0.77 0.73 0.10 0.09 0.09 40 1.11 1.07 1.08 0.09 0.09 0.09 60 1.30 1.32 1.31 0.09 0.09 0.09 80 1.48 1.47 1.46 0.08 0.08 0.08 100 1.55 1.54 1.54 0.09 0.08 0.08

From the table above I then generated an average table, showing the average current and average voltage, from those two sets of results I generated an average resistance for each of the different intervals.

 Length (cm) Average voltage Average current resistance 20 0.75 0.09 8.30 40 1.08 0.09 12.00 60 1.31 0.09 14.50 80 1.47 0.08 18.30 100 1.54 0.08 19.25

The experiment was undertaken three times in the time given. The average table was accumulated by the results I had generated when carrying out the original experiment. The average results were rounded to two decimal points as this inserts a common denominator.

I carried out the experiment in the simplest and the most safest way possible.  I was firstly going to measure the voltage and current at every 10cm intervals, but because there was insufficient amount of time, I could not do so. Me and my group also started out experiment slightly later than any of the other groups because we did not have all the equipment needed to complete the experiment.

On the next page it shows the average relationship between: average voltage and resistance, average current and resistance, and finally it shows the average resistance of all three attempts.

When looking at my average resistance graph I found I had two anomalous results. I will explain about that in the next part of my coursework.

If I took a result at every 10cm I think I would have got a better and more accurate result because I would have generated more readings.

Analysing

Finding

After  carrying out my experiment I have to analyse my finding. From my findings I can confidently  say that the rate of resistance increases as the length of the wire increases. This is because the number of electrons in the wire increases when the length increases. Also I found out that as the resistance increases the current decreases at an equal rate. The vibration of the fixed, metallic atoms within the wire creates an opposition for the free electrons. If there is more resistance then that means the electrons are having a stronger force opposing them. This causes the current in the wire to decrease at the same rate as the resistance increases. This shows that there is a directly proportional relationship between the two.

Graph analysis

With the experiment taken out, I formulated two tables, one consisting of three attempts at the experiment and the second table showing the average current, voltage and resistance. From these tables I generated three graphs. One showing the average voltage, another showing the average current and the final graph showing the average resistance. For the average resistance I drew a line of best fit, and from that line I found out I had two anomalous results.

After analysing the graph I can say that there are many things which can be mentioned. There is a direct proportional relationship between the length and resistance. The results were not exact but they were good enough to see the relationship. The results didn’t come out as good as possible because of the lack of equipment . I can clearly see from the graph that as the length increases so does the resistance.

Trends-

• I found out that as the length increases so does the resistance and in both the average voltage and the average resistance I found out that both had a positive correlation, that means that as one variable increases so does the other. Length is an independent variable and so it increases. However resistance could increase or decreases depending on the current flow and other variables. At 20cm the resistance was 8.30 and at 100cm the resistance was 19.25. this shows that there has been an increase in the resistance as the wire lengthened.
• I also found that my average voltage went up by approximately 0.15 to 0.20 volts every 20cm interval.

Conclusion

Current

Finding out the current was an important part of this experiment. So it had to be as accurate as possible, this could not be achieved at its best but it was good enough simply because the crocodile clips were larger in area then the nichrome wire, so this meant some of my results were 2 to 3mm off.

 Current (A) Length (cm) 1st 2nd 3rd 20 0.10 0.09 0.09 40 0.09 0.09 0.09 60 0.09 0.09 0.09 80 0.08 0.08 0.08 100 0.09 0.08 0.08

As you can see from the table above the current most of the time stayed constant, there was not any major changes. Apart from the first reading of 20cm, I thought that was a bit odd because I didn’t get any other results which were 0.10. But overall the current only changed about 0.01 amp, this was expected due to lack of equipment.

Conclusion

I found out from working on this experiment that the prediction I made at the beginning of this experiment was correct. I predicted that as the length increases so will the resistance. The length and the resistance did not have a directly proportional relationship because some results were anomalous, and this was due to lack of equipment and time.

Overall this experiment went fairly well, I say this because I got the results I wanted on a good basis and also I did it in the quickest and easies possible way, without anyone getting hurt. I could have improved this experiment by taking into consideration improvements earlier mentioned in this coursework, if I did this experiment would have come out even better and accurate.

But overall this experiment was a success because the results generated proved the length does affect the resistance of a nichrome wire. The results derived gave me a good basis to base my finding on.

Krishna Patel 10G

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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