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# Resistance of a Wire Investigation

Extracts from this document...

Introduction

Michael Laws                01/05/07

### INTRODUCTION

I have been given the task to investigate how the resistance of a wire is affected by the length.  I will investigate, predict possible results, do the experiment and analyse assess my results to my degree of judgement and knowledge.  Any analogous result I will record and investigate why they are abnormal.  I will also try to find any correlation between my results.

## SCIENTIFIC BACKGROUND

I had very little knowledge about this subject before this coursework came along.  I did a small amount of work in Design and Technology last year.

The resistance of a conductor depends on two things:

1. Its dimensions
2. The material it is made of
1. A thin wire has a high resistance than a thick wire. A long wire has a greater resistance than a short one
1. The material the conductor is made of affects its resistance.  A good conducting material has more ‘free electrons’ in the outer shell of their structure.  If the electrons can flow easily through this material, it is resistance is lower.

For example, gold has more free electrons than iron, because of this   it is a better conductor.

This Information is from the book ‘Physics Know How’.  Written by John Harrison

The resistance is measured in ohms.  Ohms (R) is equal to the electromotive force or potential difference, in volts (V) divided by the current in amperes (I).

Atoms are made up of a positively charged nucleus surrounded by

negatively charged electrons.

Middle

0.48

0.3

Nichrome

103

1

Manganin

42

0.1

Copper

1.56

43

## PRELIMINARY WORK

For my preliminary work, I used a computer program on the school network to recreate the experiment.  These results were obtained from a circuit using 26 SWG constantan wire, the circuit will be powered by a power pack:

 Length of wire (m) Current (A) Voltage (V) 1.6 0.20 0.99 1.5 0.22 0.97 1.4 0.21 0.96 1.3 0.24 0.87 1.2 0.25 0.90

These are my results I acquired from my preliminary results.  I have used 26 SWG constantan wire.   Constantan has the lowest resistance; this can be seen in the first table with the resistances of four wires.  In my actual investigation, I will use constantan at a SWG weight of 28.  This is because the wire will have a lower resistance than say if the SWG of the constantan was 32.

#### KEY FACTORS

Heat

An increase in heat increases the resistance.  This is due to the increased vibration of atoms and the higher chance of the electrons colliding with them.

Width

An increase in the width decreases the resistance.  This is because the electrons have a wider course to flow and has less chance to collide.

Length

An increase in the length increases the resistance.  This is because the electrons have further to travel in one second.

Density

A higher density will increase the resistance.  This is down to the increased number of atoms in the same amount of space.  This creates a much higher chance of collisions.

Material

Different conductors materials will have different resistances.

Conclusion

### METHOD

• Set up the apparatus as shown in the diagram on the previous page.
• It is important that the voltmeter is set up in a parallel circuit and the ammeter in a series.
• Take readings at equal intervals of 10cms.
These lengths will be:

2 metres

1.9 metres

1.8 metres

1.7 metres
1.6 metres

1.5 metres
1.4 metres

1.3 metres
1.2 metres
1.1 metres

1 metre

0.9 metres

0.8 metres

0.7 metres
0.6 metres

0.5 metres

0.4 metres

0.3 metres

0.2 metres

0.1 metres

• Accuracy is paramount so readings will be taken to two decimal places.
• The reading from the ammeter will be used to work out the resistance.  This will be done using Ohms Law: (V=IR).  This can be rearranged to,
R     =    V
I

## FAIR TEST

To ensure that the experiment is carried out in a fair way and that the results will be accurate.  I will only vary the length of the wire, this will be the only thing I will vary.  The wire must be pulled tight against the ruler and taped in place to ensure the length is accurately measured and that there are no kinks or bends in the wire to avoid an incorrect result.  The same circuit and power pack must be used throughout as different batteries may have different voltages if they are old.  The experiment should be repeated more than once and an average taken to make sure that the results are reliable.  I will take twenty results to make sure that they are wide spread.  I will repeat the experiment twice, and take both the average of

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