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My aim in this experiment is to investigate how the length of a wire affects its resistance.

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How does the length of a wire affect its resistance?


My aim in this experiment is to investigate how the length of a wire affects its resistance.

Background Knowledge

Resistance is a measure of how an object opposes the flow of an electric current. When electrons pass through a wire they collide with the atoms within the metal. When this happens the electrons lose energy. The more collisions that occur the more energy the electrons lose. The metal atoms in the metal wire obstruct the moving electrons causing the collisions, which slow down the electrons from reaching their destination. Resistance restricts the flow of charge, so the greater the resistance the smaller the current. Georg Simon Ohm discovered that ‘the current through a metallic conductor is directly proportional to the voltage across its ends if the temperature and other conditions are constant’.

        Resistance can be calculated by dividing the voltage (V) by the current (I). It is measured in Ohms (Ω).


I will carry out a preliminary experiment to help me come up with an initial theory and so that I can see if my plan works in practice, if I experience any problems I can correct them for my final experiment, this will help me ensure that my results are reliable.

...read more.


The apparatus I am going to use for my experiment is:

  • A variable resistor to change the current, which will as a result change the resistance
  • An ammeter to measure the current
  • A voltmeter to measure the voltage
  • A d.c. power supply to provide the electricity
  • 8 different lengths of 30 swg constantan wire (25, 50,75,100, 125, 150, 175 and 200cm)
  • 2 crocodile clips
  • A meter stick to measure the different lengths of wire
  • Pliers to cut the wires
  • Connecting wires


To make my experiment a fair test I will have only one input variable (the length of wire) and all the other factors shall remain constant:

  • The current will be controlled by using the variable resistor
  • I will use the same cross section area and material of wire
  • The equipment I use will be the same throughout the experiment

Temperature also affects the resistance of a wire, but with the wire I have chosen to use-constantan, the temperature has no affect on its resistance so I will not have to worry about this factor.


My input variable is the factor I am changing, the length of wire. My output variable is what I am investigating, the resistance.


The values of my input variable will range from 25cm (lowest input variable) to 200cm (highest input variable) of wire. I will use 8 different lengths of wire; this will give me a wide range of readings and ensure I obtain accurate results.

...read more.


This result could be because I may have miss read the reading on the voltmeter or I recorded the wrong result. Or I may have not placed the crocodile clips right at the end of the wire; they may have been placed slightly away from the ends of the wire.

Reliability of Evidence

I used a suitable range of results for my experiment. The relationship I found between my input and output variable would also be true for another set of values. I took two sets of results and both sets are very similar. If I repeated my experiment I would come up with the same set of results.

Suitability of the Procedure

My investigation could be improved by repeating the experiment more times; this would help me obtain a more accurate result. I could use an Ohmmeter, which would give me the resistance directly instead of me having to calculate it. Or to obtain even more accurate results I could use data logging, this would reduce the chances of human error.

Further Work

I could investigate the other factors affecting resistance to find out more:

  1. The effects of changing the cross section of a wire
  2. Changing the temperature of the component
  3. Using different materials of wire

...read more.

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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