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Resistance of a Wire Coursework

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Introduction

Resistance of a Wire Coursework

I have been asked to find out what affects the resistance of a wire.   I have decided to go about this by seeing how changing the length of a wire affects the resistance.   One of the first things I have to do is select which wire I am going to carry the experiment out on.   In order to do this I carried out an experiment on different wires, with the wire being 10cm and 20cm long.   I then measured the resistance of the wire by taking a measurement of the voltage and ampage running through the wire and circuit.  The circuit I used looked like this:

Another factor that will affect which wire I choose will be the cross-sectional area of the wire, because I only have wires that are 28 or 26 swg, except for one, which is 36 swg, and the resistance will be affected too much by the wire heating up.

These are the results from our small experiment -:

Length (cm)

Current (Amps)

Potential Difference (Voltage)

Resistance = V

(2d.p.)              I

Constantan

20cm

10cm

1.96

3.50

3.39

2.62

1.73

0.75

Brass

20cm

10cm

7.13

7.99

0.77

0.44

0.11

0.06

Chrome

20cm

10cm

2.57

3.66

3.43

2.51

1.33

0.69

Copper

20cm

10cm

8.33

8.34

0.22

0.23

0.03

0.03

Aluminium

20cm

10cm

1.34

2.37

4.15

3.38

3.09

1.43

...read more.

Middle

(+ 1cm)

20cm

2.75

2.92

1.0

(+ 1cm)

30cm

2.22

3.30

1.4

(+ 1cm)

40cm

1.69

3.40

2.0

(+ 1cm)

50cm

1.37

3.61

2.6

(+ 1cm)

60cm

1.32

3.77

2.8

(+ 1cm)

70cm

1.15

3.89

3.3

(+ 1cm)

80cm

1.05

3.94

3.7

(+ 1cm)

90cm

0.96

4.08

4.2

(+ 1cm)

100cm

0.85

4.11

4.8

Experiment 2

Length

Amps

Volts

Resistance

(+ 1cm)

10cm

3.58

2.16

0.6

(+ 1cm)

20cm

2.80

2.86

1.0

(+ 1cm)

30cm

2.13

3030

1.5

(+ 1cm)

40cm

1.79

3.52

1.9

(+ 1cm)

50cm

1.48

3.62

2.4

...read more.

Conclusion

the measurements should be taken 5 seconds after the power has been switched on, then the wire will not have enough time to heat up (affecting results)

all data will be taken at the relative same time

My results were in my opinion measured to the highest level of accuracy given the apparatus we had available to us.   The most important change which would affect our experiment would have to be the powerpack, which although being set on 6 volts, when we had to use a different powerpack, the voltage would be different by up to ½ a volt more or less, although this does not affect the resistance when worked out.   If any anomaly occurred it would be easier to spot because you could look back at the bare information and it would “glare”.

Therefore, if I repeated my experiment, in order to achieve more accurate results to show that if length is doubled so is the resistance, I would:

  • Use more accurate measuring equipment
  • Use a more accurate power supply
  • Measure the wire twice to check length
  • Repeat the experiment more time to increase accuracy

Andrew Shand 11S1

...read more.

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