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# The Resistance of a wire.

Extracts from this document...

Introduction

Ashley Munns

Physics Investigation:

The Resistance of a wire

The task we have been set is to investigate what affects the resistance of a wire.

The 4 different variables that affect the resistance of a wire are:

• Length of the wire
• Area of cross-section of the wire
• Material of the wire
• Heat

In every circuit there is a current, I, a voltage, V, and a resistance, R.  The current is measured in amps, A, the voltage is measured in volts, V, and the resistance is measured in ohms, Ω.  To measure these different variables we can use a variety of equipment.  To measure the current we use an ammeter.  To measure the voltage we use a voltmeter. To measure the resistance you need to find the voltage and divide it by the current.  There is a simple triangle that we can use to find one of these variables, provided that you know what two of the others are.

Ohm’s law

Ohm’s law says that the current flowing through a metal wire is proportional to the potential difference across it providing the temperature remains constant.

So he came up with this equation:

Resistance, R = p.d across the wire (v)

Current through the wire (I)

From this information he came up with this graph:

This graph is an ideal ohmic conductor.

Middle

50

0.8

0.9

0.8

0.833

7.6

7.8

7.8

7.733

60

0.9

0.9

0.9

0.9

7.2

7.2

7.3

7.233

70

0.9

0.9

0.9

0.9

5.8

6

5.4

5.733

80

0.9

0.9

0.9

0.9

5.2

5.4

5.8

5.467

90

1

1

0.9

0.967

4.2

4.4

4.6

4.4

100

0.9

0.8

0.8

0.833

4.4

4.8

4.6

4.6

110

0.9

0.9

1

0.933

4.1

4.4

4.4

4.3

120

0.9

0.9

1

0.933

3.8

3.9

3.9

3.87

This is my table of results that I got when I did my preliminary testing.  I was testing to see whether I was doing my experiment fairly and to see whether I would encounter any problems.  When I was setting the experiment up, I found that the voltmeter was faulty and that a few of the crocodile clips were also faulty.  After finally setting up the experiment with everything working correctly I was able to collect the above results.

The experiment worked well and we found that a stronger ammeter is needed to measure below 40cm because otherwise the needle went off of the scale.

Method

Equipment:

• A metre ruler
• Crocodile Clips
• Power Pack
• An ammeter
• A voltmeter
• A length of wire (roughly 150cm)

A length of wire is taped at both ends to a metre rule.  It is then attached to a circuit consisting of an ammeter in series and a voltmeter in parallel. One crocodile clip will be permanently placed at one end of the wire and another crocodile clip will be moved along the wire to produce different lengths for us to take readings from.  I will take readings from the voltmeter and from the ammeter and put these into a table.

Conclusion

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1.21

1.20

0.58

20

0.83

0.83

0.83

0.83

0.85

0.87

0.85

0.85

0.97

30

0.91

0.91

0.92

0.91

0.65

0.66

0.65

0.65

1.40

40

1.00

0.97

0.97

0.98

0.53

0.52

0.52

0.52

1.88

50

1.02

1.03

1.02

1.02

0.44

0.42

0.43

0.43

2.37

60

1.06

1.06

1.05

1.06

0.38

0.38

0.38

0.38

2.79

70

1.09

1.10

1.08

1.09

0.34

0.33

0.33

0.33

3.30

80

1.11

1.11

1.11

1.11

0.29

0.29

0.30

0.29

3.83

90

1.13

1.13

1.13

1.13

0.27

0.27

0.27

0.27

4.19

100

1.15

1.14

1.14

1.14

0.25

0.25

0.24

0.25

4.56

110

1.16

1.16

1.16

1.16

0.21

0.22

0.22

0.22

5.27

120

1.17

1.18

1.17

1.17

0.20

0.20

0.21

0.20

5.85

From my graph I have found out that the resistance increases as the length increases.  From my graph I have found that Ohm’s law works and that the resistance is proportional to the length of the wire.

Examples of this are:

30cm: 1.4 Ω

60cm: 2.79Ω

40cm: 1.88Ω

80cm: 3.83Ω

On my graph I have drawn a line of best fit so that I would be able to accurately predict the resistance of a length of wire that I have not yet measured.

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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