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Investigating the Resistance of a Wire

Extracts from this document...

Introduction

Lottie von Bertele

Investigating the Resistance of a Wire

Plan

In my investigation I am going to investigate the factors which affect the resistance of a piece of wire.

The factors affecting the resistance of a piece of wire are;

• Length *
• Thickness (area)
• Type of metal

I am going to investigate how the length affects the resistance of the wire.  I have chosen length as I think it will be the most practical factor to obtain results from.  This means that I shall have to keep the other factors exactly the same throughout the experiment to make it a fair test.  I shall do this by using the same piece of wire all through the experiment.

Resistance is the force which opposes the flow of electrons in a current.  It is measured in Ohms (Ω).

To find the resistance you use Ohms Law.  This is V = IR, it can be arranged to

R = V/I.

To find the current (I) and the voltage (V) to work out the resistance I shall use an ammeter and a voltmeter.  The voltmeter shall be in parallel.

Apparatus

• Voltmeter
• Ammeter
• Rheostat
• 1 m length of wire attached to a stick
• Power pack
• Crocodile clip
• Meter ruler
• Blue tack

Diagram

Method

Set up the circuit in a methodical way, remembering that the voltmeter is in parallel, make sure the power pack is set on 2 Volts.  It must be set on a low voltage so that it won’t affect the resistance of the wire.

I have previously done an experiment just measuring the resistance of the circuit and I have learnt that if it was set on a high voltage then the temperature of the wire would increase and therefore the resistance would be affected as the electrons would bump into the atoms more frequently.  The electrons would then give the atoms some energy and make them vibrate.  We feel this vibration as heat.  When the atoms vibrate they take up more space and it’s harder for the electrons to pass them – that is why the resistance goes up.  Here is a graph plotting V against I.  This is not what I am going to do but I think it illustrates what would happen to my results if the temperature increased.

I know this would be wrong as I know that the resistance is directly proportional to the length.  Therefore I am expecting my results to look like this.

I predict that as the length of the wire increases so too will the resistance of the wire.  I think this because the current would have further to travel as the length increases and therefore there would be more electrons in the circuit to pass.

Record the results at 10cm intervals along the wire e.g. 10, 20, 30.  To make it accurate blue tack the piece of wood with the wire on it to the bench and then stick the metre ruler along side it.  Keeping the rheostat in the same position clip the crocodile clip at each place along the wire.  For each position read the Volts and the Amps.  Once all 10 positions have been done move the rheostat and repeat procedure.  Then find the average of the two resistance results.  It is better to do the procedure more than once to obtain more accurate results as the numbers on the voltmeter and ammeter may flicker.  Plot a graph using length of wire and average resistance.

Safety

• Make sure Voltage is low
• Don’t do smaller than 10cm to avoid wire melting
• Ensure good connections in circuit to avoid unwanted resistance

Middle

7.00

Wire 2

Nichrome

34

0.08

2.02

25.25

Wire 3

Mangarin

26

0.17

0.61

0.94

Wire 4

Constantan

28

0.16

0.82

5.13

Wire 5

Nichrome

22

0.18

0.54

3.00

Conclusion

From this information I have chosen to use wire 1.  This is because the resistance of the wire is not too big or too small.  If the resistance of the wire was too big such as in wire 2 the amps would be too small and my results would not be very accurate, therefore I think wire 1 is suitable.

Results

Conclusion

Evaluation

I thought that the experiment went well as I didn’t have any difficulties with it.  I think that my results are suitable and as expected as there are no anomalies.  I think they could have been a bit more accurate though, as in the example above it is not what it is expected to be although it is similar.  This is because the numbers on the voltmeter and ammeter were flickering.

To secure my results even further and make them more reliable I could do some additional experiments such as

• Doing this experiment again but collecting more data by changing the position of the rheostat five times instead of only two times.
• Doing the same experiment as before but controlling other factors such as type of metal and width.

These extra tests would give me further information about the resistance of a wire and hopefully support the conclusion I have come to in this experiment.

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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