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# Investigate how increasing the length of a wire affects the wires resistance.

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Introduction

Christopher Finch

## Resistance

Aim:

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

Prediction:

I predict that increasing the length of the wire will increase the resistance. Metals are made of millions of tiny metal crystals.  Each crystals atom is arranged in a regular pattern.  The metal is full of free electrons that do not stick to any particular atom.  They fill the space between atoms in the metal.  There is an electric current when these atoms move.

The quantity of resistance in an electric circuit determines the amount of current flowing in the circuit for any given voltage applied to the circuit. The amount of resistance depends on the type of wire used.  Resistance also depends on the thickness of the wire.  Metal atoms get in the way of travelling electrons.  This causes resistance. I predict that the use of a longer wire would increase the level of resistance.  The longer the wire that the current must pass through, the more metal atoms are present to get in the way of the travelling electrons.

Equipment:

• 100cm Nichrome wore (28swg)
• Heat proof mats.
• Circuit wires
• Power pack
• Crocodile clips
• Voltmeter
• Ammeter
• Meter ruler
• Stopwatch.

Diagram:

Method:

• This experiment shall be repeated numerous amounts of times so that the result average will be more accurate. I will be investigating how increasing the length of wire will affect resistance.  The circuit shown in the above diagram must be set up with the voltmeter in series.  The current from the power pack must be kept at 5 volts for it to be a fair test.  The wire must be joined to the circuit, it must also be placed onto of a heatproof mat, and this is because the current flowing through the wire will make the wire heat up so it could be dangerous. The wire will be used in the same way as a variable resistor.  The wire needs to be straightened and taped to the heatproof mat.  This will stop the wire changing shape. This would mean that the lengths would not be accurate, and so it would not be a fair test.  Place one crocodile clip at one end of the piece of wire, and the other needs to be 10cm away from the first crocodile clip.  Turn the power pack on so that the current begins to flow, after the current has been flowing for 5 seconds readings must be taken from the voltmeter and ammeter.  Then immediately switch off the power pack and wait for the wire to cool.  Move the 2nd crocodile clip another 10cm away from the first.  This would mean that it is 20cm away.  Then again take readings as before.

This needs to be repeated so that readings are obtained every 10cm till 10cm’s is reached.  The results need to be recorded in a table so that they can be compared.  The experiment needs to be repeated three times with a new piece of wire, which has the same properties and thickness.  Repeating the experiment 3 times will give enough results so that an average can be obtained and charted.

• Repeat the experiment, but this time with the same metal but of a different thickness so the two can be compared.  There will not be sufficient time for this variant to be carried out.

Middle

0.55

8

100

4.5

0.5

9

2nd set of Results

 Length of wire used (cm) Voltage Current (I) Resistance (Ω)Voltage/Current 10 2.5 2.5 1 20 3.1 2 1.55 30 3.75 1.5 2.5 40 3.5 1.4 2.5 50 3.9 1.1 3.54 60 4.1 0.9 4.55 70 4.1 0.8 5.13 80 4.15 0.7 5.93 90 4.4 0.6 7.3 100 4.5 0.5 9

3rd Set of Results

 Length of

Conclusion

If I were to do the experiment again I would also different metals and thickness of wire, this would give me a better more varied experiment. It would also be better for my averages if I were to repeat the experiments more times to be able to find more accurate averages.  If the experiment were to be repeated I would not allow the metal wire to heat up as much as it did.  Heating obviously affected my results; they would be more accurate if the wire did not get so hot whilst doing the 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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