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# What factors affect the resistance of wire?

Extracts from this document...

Introduction

Katherine Short 10F1

What factors affect the resistance of wire?

Plan

The aim of this investigation is to find out what factors affect the resistance of wire and how.  Once, through my research, I have found out those factors I am going to select one to do my experiment on to prove that it is correct.

There must be a potential difference (voltage) across to make a current flow through a conductor.

This is the formula to work out the resistance of a wire:

Resistance (Ω) = Potential Difference (V)

Current through conductor (A)

R = V                Where R = Resistance, V = Pd (Voltage), I = Current

I

V = IR                and I = V

R

Factors affecting resistance

• Length – Doubling the length of a wire doubles its resistance.
• Cross sectional area – Halving the width of the wire doubles its resistance.  So a thin wire has more resistance then a thick one.
• Material – Copper-connecting wire is a good conductor and a current passes through it easily.  A nichrome wire has more resistance then a copper wire of the same size.
• Temperature – For metal conductors, resistance increases with temperature.  For semi-conductors, its decreases with temperature.

##### I am going to investigate how length affects the resistance of a wire.

Middle

Two crocodile clips

##### Method

Collect the above apparatus and assemble as shown above. Then keeping the voltage the same for every reading, measure the current with the wire at different lengths.  Start at 100 centimetre and move down in increments of 10.  When you get to 10 go down in increments of 1.  Take 3 readings for each length.  Record your results to work out the resistance using this formula:

V/I = resistance then make an average of the 3 readings.

I am going to take 3 readings for each length from 100cm to 1 cm.

##### Trial Experiments

First of all I needed to see how much voltage it takes to heat up the wire.  I needed a high voltage but not so much that the heat would affect my results because it’s a factor that affects the rate of resistance.

These were the first set of results we got:

 Length Voltage(Volts) Current(Amps) Resistance (ohms) 10cm 2 0.51 0.255 10cm 2 0.51 0.255 10cm 2 0.52 0.26 9cm 2 0.52 0.26

From this I realised the wire was already getting too hot.  I also tried a much higher voltage of 4.5 with a longer length wire.  This also got warm so I decided to have a voltage of 5 when taking readings from 100cm to 10 cm.  I decided to lower the voltage to 0.

Conclusion

I think my method was good.  This is because I got constant results with only one anomalous.  There was a steady correlation and the results matched up to what I had predicted.

To get more reliable and accurate results I could use ammeters and voltmeters that go to more decimal places i.e. further then to the nearest hundredth.  I would need to use new wire each time because throughout the experiment we got kinks in the wire.  This would have changed my results because it alters the length of the wire.

To help back up what I have already done I could investigate the other factors that affect resistance.  I could try the same experiment again but get a wider range of results.  I would do this buy using wire longer then 100cm and I could measure in increments smaller then 10 cm.  I could also repeat my experiment more times,  for example do each length 5 times.

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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