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An investigation into the relationship between the length of a wire and its resistance.

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Introduction

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Aim

In this investigation I, overall, aim to see if the length of a wire affects its resistance. I will do this investigation in different stages. In the first stage I will find the resistance of the wire using a digital ammeter and voltmeter. In the second stage I will find the resistance using an analogue ammeter and voltmeter. And in the third stage I will find the average diameter of the wire using a micrometer.

Prediction

     I think that the longer the wire is the more resistance it will have. This is because the electrons in metals are free to move about from atom to atom. This is called a ‘sea’ of electrons. As soon as a potential difference is passed through the metal these electrons move faster causing harder collisions against the atom walls, though they can still pass through the atoms. This causes friction, which converts the potential difference into heat energy, which gives the wire its resistance. The longer the wire is the more collisions there are so there is more resistance.

     In order to ensure that all of my results are accurate I will have to keep all of the variables, things that could possibly change, the same (as explained below) except the one that I am investigating, the current.

     

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Middle

35

0.65

0.41

40

0.65

0.37

Length (cm)

V (v)

I (a)

5

0.65

2.75

10

0.65

1.41

15

0.65

0.96

20

0.65

0.73

25

0.65

0.58

30

0.65

0.49

35

0.65

0.42

40

0.65

0.36


Analogue Meters

Length (cm)

V (v)

I (a)

5

0.65

3.10

10

0.65

1.61

15

0.65

1.10

20

0.65

0.85

25

0.65

0.65

30

0.65

0.55

35

0.65

0.45

40

0.65

0.35

Length (cm)

V (v)

I (a)

5

0.65

3.00

10

0.65

1.65

15

0.65

1.05

20

0.65

0.85

25

0.65

0.65

30

0.65

0.55

35

0.65

0.45

40

0.65

0.40


Micrometer Readings

Length along wire (cm)

Diameter (cm)

10

0.35

20

0.36

30

0.37

40

0.36

Length along wire (cm)

Diameter (cm)

10

0.35

20

0.36

30

0.36

40

0.36

Average Micrometer Readings

Diameter (cm)

Cross-Sectional area (cm2)

0.36

0.10 (1mm)


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Conclusion

Evaluation

     I think this experiment could have been improved because as you were measuring the resistance of the wire the wire was getting hotter as the current was passing through it, which increased its resistance. If you keep the crocodile clip on the wire for a shorter amount of time you get a truer measurement of the resistance of the wire at room temperature. The experiment could also have been improved by adding new variables e.g. the cross sectional area of the wire could be altered. If this were altered I would expect the resistance to decrease as the friction caused would decrease. I could also change the material of the wire. If it was a more dense material it would have a higher resistance but if it was less dense it would have a lower resistance as there is less friction so less heat. I could also change the temperature of the wire. I would expect the wire to have a higher resistance as it got hotter.

...read more.

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