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Resistance of a wire.

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Resistance of a wire

There are a range of factors that can affect the rate of resistance in a wire.

These include:

  • Length of wire
  • Thickness of wire
  • Temperature
  • Material

For my investigation I have chosen the first factor, the length of wire. I will see how the length affects the resistance.

Resistance is the property of an electrical conductor, to work against the flow of the current and change some of the electrical energy into heat. 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, according to Ohm's law. The unit of resistance is the ohm and the amount of resistance that limits the passage of current to one ampere when a voltage of one volt is applied to it happens. The standard abbreviation for electric resistance is R and the symbol for ohms in electric circuits is the Greek letter omega, Ω.


Resistance = potential difference / current

                = V/I

So therefore in order to find the resistance I will need to find the potential difference and the current in the circuit.

Now I will explain the potential difference briefly. It is the potential difference that pushes electrons around the circuit. So if the wire has more electrons then there will be less current thus a higher resistance eg. 6 volts / 3 amps = 2 ohms resistance. Therefore if there was 6 volts but 2 amps, the resistance would be 3 ohms.

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(See graph overleaf)

From my preliminary work I can see that the resistance follows a distinct pattern as it is rises 0.6 ohms at each length. I am rather pleased with my results as they are perfect but it should be different when I carry out the final experiment.

Therefore I have learnt that I am going to change the current in the final experiment to 0.2A but the lengths I have chosen seem to be good. So I will stick with the 0.1m increments up to 1m. I also know that I’m certainly going to use the constantine wire with s.w.g 24. This is instead of using copper or nickel wire. I have decided to us constantine because it keeps the resistance constant no matter what the temperature is. With copper, if the temperature changes, so does the resistance. I have gone with s.w.g 24 as it gives a nice range, an even spread on the graph. It is a nice range between s.w.g 16 to 36.

Final Method

  • Take safety considerations first
  • Set up the circuit as shown in the diagram below, excluding the voltmeter.
  • Place the crocodile clip at 0.1m on the metre stick. Turn on the power supply and check the ammeter is working i.e. getting some current.
  • Turn the knob on the power pack until the current reads 0.2A on the ammeter. This will stay constant throughout the experiment.
  • Turn the power supply off.
  • Then connect the voltmeter. Turn the power pack on, which is already set.
  • Take the readings from the ammeter and voltmeter
  • Turn the power supply off after recording the current and voltage due to the fact extra heat is generated that could increase resistance.
  • Move the clip to the next increment, 0.2m. Repeat the same steps above for each 0.1m increment.
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I think the experiment was fairly successful and the procedure suitable, although not as much as I would have liked it to be. For a start we used a crocodile clip to connect the wire at a certain length. The crocodile clip is fairly wide so it would be impossible to connect it to the wire at exactly the desired length. Also the wire may not have been completely straight and so we might have actually been observing the results for the exact length we intended.

I think my results were quite good and vaguely followed a pattern. This is because we used a good range of increments. The 10 increments allowed us to draw up a valid conclusion.

There were no anomalies, which proves the reliability of my results. Despite the fact there are no anomalies, my results were not directly proportional.

I think that some other failures could come down to human error e.g. I could have simply misread the ammeter or voltmeter or made a mistake when calculating the resistance. Also other factors such as temperature could have had a diverse effect on the resistance.. This extra variable would have made the experiment unfair.

If I was to repeat the experiment, I would use a wider range of results in order to increase their reliability. Also I would do repetitions with each one. For further work one could see the resistance of other wire with the temperature and width. Also you could use different resistors such as the thermistor (how resistance varies with heat) or a light dependant resistor.

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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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