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An investigation to find out how the electrical resistance of a wire changes in relationship to its length

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An investigation to find out how the electrical resistance of a wire changes in relationship to its length.

Key Variables

A) Potential difference across the wire

B) Resistance of the wire, which includes:

   -Temperature of the wire

  -Material of the wire    *

  -Length of the wire

  -Cross-sectional area of the wire

N.B. * = discreet variable e.g. Changed in discreet amounts

The Variable I will investigate

I am going to find out how the length of the wire affects the current and the electrical resistance.


I think that as the length of the wire increases the current will decrease thus resistance will increase. I also believe that the rate at which the resistance of the wire increases will be directly proportional to the length. Thus if the length is doubled the resistance should also double.This is because if the length is doubled the number of atoms will also double resulting in twice the number of collisions slowing the electrons down and increasing the resistance.

Predicted Graphs


 With electricity, the property that transforms electrical energy into heat energy, in opposing electrical current, is resistance. A property of the atoms of all conductors is that they have free electrons in the outer shell of their structure.

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Measurements and Accuracy

I will use the metre ruler to measure five different lengths of wire: 10cm, 20cm, 30cm, 40cm and 50cm. I am doing the experiment at five different lengths to make sure I get a big enough range to be able to comment on. I will then repeat these five results for reliability and so I can average my results also so I can spot and discard any anomalous. To keep this experiment as accurate as possible we need to make sure that the length of the wire is measured precisely from the inside edge of the crocodile clips, making sure that the wire is straight when we do this. We must also make sure that the wire is straight when we conduct the experiment. If it is not, short circuits may occur and bends and kinks in the wire may affect the resistance. The voltage will be measured using a voltmeter and current will be measured using an ammeter. I will also use a variable resistor to acquire my required voltage. To maintain accuracy the reading of the voltage, adjusting of the voltage and reading of the current should be done fairly promptly after the circuit is connected.

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The next modification I would make would be to use pointers instead of crocodile clips; I would do this because pointers would be more accurate. The pointers would be more accurate because the tips have a much smaller area than the crocodile clips giving a more accurate measurement of the length of wire.
As well as making these modifications I would also improve my Investigation by expanding on it, investigating another factor long side i.e. the width, and working out the cross-sectional area.

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