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Resistance of a wire

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Introduction

Siddrah Farid

Resistance of a wire

Aim: To investigate how the resistance of a wire is affected by the length of the wire.

What is resistance?

   Electricity is conducted a wire, by way of free electrons. The amount of free electrons depends on the material and more free electrons means a better conductor, i.e. it has less resistance. For example, gold has more free electrons than iron and, as a result, it is a better conductor. The free electrons are given energy and as a result move and collide with neighbouring free electrons. This happens across the length of the wire and thus electricity is conducted. Resistance is the result of energy loss as heat. It involves collisions between the free electrons and the fixed particles of the metal, other free electrons and impurities. These collisions convert some of the energy that the free electrons are carrying into heat.

How is it measured?

   The resistance of a length of wire is calculated by measuring the current present in the circuit (in series) and the voltage across the wire (in parallel). These measurements are then applied to this formula:

V = I X R          where V = Voltage, I = Current and R = Resistance

This can be rearranged to:

R = V/I

Ohms law

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Middle

I attached the positive crocodile clip is attached at 0cm.And used the negative to move up and down the wire, stopping at 10, 20, 30, 40…..100cm.Each time reading the ammeter and voltmeter to work out resistance R = V/I.

Results

   Having completed two sets of results for one wire, it was noticed that these was a large black mark towards one end of the wire, where it appeared that it had been melted to some degree at some point. It was therefore decided to conduct experiments on

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Conclusion

0.52

0.28

1.85

70

0.35

0.18

1.94

80

0.25

0.25

2.08

90

0.44

0.6

0.73

100

0.64

0.21

3.047

Results table 3

Length (cm)

Voltage (V)

Current (I)

Resistance (R)

10

0.10

0.33

0.30

20

0.19

0.32

0.59

30

0.28

0.32

0.87

40

0.36

0.31

1.16

50

0.44

0.30

1.46

60

0.51

0.30

1.7

70

0.59

0.29

2.03

80

0.66

0.28

2.35

90

0.73

0.28

2.60

100

0.80

0.27

2.69

Conclusion

   After completing the experiment I have found that my prediction was quite accurate. The resistance rose as the length of the wire increased. As I have mentioned in my prediction this is because the longer the wire, the more times the free electrons will collide with other free electrons. After looking at my graph I noticed that I have to anomalous results which could have been due to an error in the measuring and or reading of the meters, or a temperature change.

Evaluation

   If I were to do this experiment again, I would use more exact ammeters and voltmeters, a further precise method of measurement, and obtain a much wider variety of readings to facilitate a more accurate average. I would also study other factors, such as temperature, voltage and current, and see how these affect the resistance. Another error may have resulted by measuring the lengths as the rulers used may not have been precise, and it proves difficult to get an exact and accurate reading of the length by the eye, as the wire also may not be completely straight. Its thickness may be diverse through out its length. These would also have counted as errors.

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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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