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Investigating How The Resistance Of A Wire Changes With Length

Extracts from this document...

Introduction

Neha Shah – 10EC/10PY

Investigating How The Resistance Of A Wire Changes With Length

AIM

To investigate the relationship between the length of wire and its resistance when a voltage is applied.

PREDICTION

If I double the length of a wire I would expect the resistance to approximately double proportionally. If I halve the length of the wire I would expect the resistance to approximately halve proportionally. I predict that as the wire gets hotter, its resistance will increase.

HYPOTHESIS

The wire allows an electric current to flow through it, but it does not allow the current to flow with ideal freedom. Electric current is the flow of electrons. This is a diagram showing atoms in the metal (which are really positive ions) surrounded by a sea of free electrons.

Collisions between the free electrons and positive ions of the conductor (wire) interfere with the flow of electrons from the current. In a collision the electrons collide with the ions in the wire and as a result they lose kinetic energy which is transformed into heat. This prevents the flow of electrons and this effect is known as resistance. 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:

                             Voltage                                 

               Current

The symbol for ohms is the Greek letter omega, Ω.

...read more.

Middle

0.68

0.84

5.55

5.88

6.00

5.88

5.95

5.85

90cms

1

2

3

4

5

0.18

0.38

0.56

0.76

0.92

5.55

5.26

5.36

5.26

5.43

5.37

80cms

1

2

3

4

5

0.22

0.42

0.62

0.82

1.02

4.54

4.76

4.83

4.88

4.90

4.78

70cms

1

2

3

4

5

0.24

0.48

0.72

0.96

1.06

4.17

4.17

4.17

4.17

4.72

4.28

60cms

1

2

3

4

5

0.30

0.68

0.82

1.02

1.12

3.33

3.45

3.65

3.92

4.40

3.75

50cms

1

2

3

4

5

0.36

0.68

1.00

1.08

1.16

2.77

2.94

3.00

3.70

4.31

3.34

40cms

1

2

3

4

5

0.42

0.84

1.22

1.98

2.20

2.38

2.38

2.45

2.65

2.79

2.53

30cms

1

2

3

4

5

0.52

1.10

1.70

2.20

2.80

1.92

1.81

1.83

1.86

1.88

1.86

20cms

1

2

3

4

5

0.90

1.62

2.25

3.22

4.02

1.11

1.23

1.33

1.42

1.43

1.30

Constantan 0.25mm

LENGTH (cm)

VOLTAGE (V)

CURRENT (A)

RESISTANCE (Ω)

...read more.

Conclusion

I think that investigation was carried out fairly and safely. We managed to keep everything the same apart from the length of the wire and voltage. We did not change the wire therefore the cross-sectional area and material of the wire remained the same. But because we used the same wire the voltage applied slowly heated up the wire without me knowing towards the end of the experiment affecting our results and giving me a few anomalous results even though we kept the voltage setting low. We could have overcome this problem by changing the wire but taking it from the same reel of wire. This way the temperature of the wire remains constant and also the cross-sectional area and material remains constant.

If I was to do this investigation again to get more reliable data I woulduse pointers instead of the crocodile clips which I used. This is because pointers are a lot more accurate, because they have a smaller surface area on their tips than crocodile clips. This in effect would give much more accurate measurements. I would also use a digital voltmeter, to get a more accurate readings of the volts.

...read more.

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