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Factors affecting the resistance of a wire

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Introduction

Yael Levey 11JS        Physics Coursework        26/04/07

Factors affecting the resistance of a wire

PLAN

  • Aim

To investigate the factors which affect the resistance of a wire

  • Prediction

My prediction is that as the length of wire is increased the resistance will increase also; it will be directly proportional. This can be explained scientifically. Current is a free moving flow of electrons. Resistance reduces the flow of electrons. This resistance occurs when the electrons, that are attracted to the positive side of the cell, bump into the fixed lattice nuclei of the material that they are flowing through. This means the path of the electrons is erratic as they are changing direction. The more material there is for the electrons to flow through the more fixed lattice nuclei there are. More nuclei mean more bumping and therefore higher resistance. Double the length of wire would mean double the amount of lattices for electrons to collide with. There will be a certain amount of lattices in a certain length of wire. These lattices will provide a certain amount of resistance. So when a wire is increased by the

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Middle

6.22

60cm

0.03

0.15

5

5.68

60cm

0.06

0.35

5.83

60cm

0.09

0.56

6.78

70cm

0.03

0.23

7.7

7.10

70cm

0.06

0.41

6.83

70cm

0.09

0.61

8.44

80cm

0.03

0.27

9

8.65

80cm

0.06

0.51

8.5

80cm

0.09

0.76

8.79

90cm

0.03

0.27

9

9.07

90cm

0.06

0.56

9.33

90cm

0.09

0.80

10

100cm

0.03

0.36

12

11

100cm

0.06

0.66

11

100cm

0.09

0.90

10

These are my preliminary results. These results tell me

  • It is clear that the resistances for 0.03A go up by 1 steadily, until 60cm when it then becomes irregular.
  •  Out of all the results there are none that are the same but the results are quite close together. The currents that I chose could have been too low to produce good results, but the range that I used (lengths from 10cm to 100cm in steps of 10cm) was good because I got a wide variety of results.
  • For these results I used Nichrome 28. I will use this diameter (0.376) in my real experiment because I can get stable and reproducible results, E.g. at 20cm they are 2Ω, 2.26Ω, and 2.78Ω.
  • I decided to use this method for my main experiment. This is because I think it is accurate and easy to use. With this method you can work out the resistance yourself rather than leaving it to a machine, which could give inaccurate results if its battery was low.
  • To make sure these results were reliable I would take an average of the results recorded, as I did for the preliminary experiment. This will help get rid of slightly bad results.        
  • Results

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Conclusion

  Problems I had in procedure were the wire not being straight and temperature of the wire increasing. This meant the experiment was a fair test only to a certain extent. To change the non-straight wire problem I would rub it with a flat-sided object, such as a hard piece of wood. This would straighten out some of the bends. To stop temperature effecting earlier results so drastically I would take reading as quickly as possible. This would give the wire less chance to heat up.

  Further experiments that would extend this work could include varying cross-sectional surface area further (rather than only trying two) and seeing how different materials effect resistance. Voltage applied and insulating the wire could also be tried.

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