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Investigate how the length of a wire affects the current and resistance of a wire.

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Physics Courswork – The Resistance of a Wire


Investigate how the length of a wire affects the current and resistance of a wire.

Prediction and Background Information

I think as you increase the length of the Constatan wire, you also increase the amount of resistance. The current is the flow of electrons; the current is dependent on the amount of voltage, which is applied. Voltage is the push given to the current. Resistance occurs when the electrons travelling along the wire collide with the atoms of the wire. These collisions slow down the flow of electrons causing resistance. Resistance is a measure of how hard it is to move the electrons through the wire. In a longer piece of wire, there would be more atoms for the electrons to collide with and so the resistance would be greater. The relationship between the wire length and the resistance should be directly proportional. This is because in a wire twice the length of another wire there would be double the amount of atoms causing the resistance.

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Resisitance is measured in omegas (Ω). The formula for this is:

Resistance (Ω) = Voltage (V) / Current (Amps)

e.g If voltage is 0.13 and current is 0.3 then 0.13 / 0.3 = 0.43 Ω

Equipment List

  • Constatan wire
  • Power Supply
  • Connecting Wires
  • Two Crocodile Clips
  • Voltmeter
  • Ammeter

Safety Precauitions:

This is not a very dangerous experiment but despite this you must always handle electricity with care, keep the current low, handle with dry hands etc.

Accuracy / Fair Test:

To keep this experiment as accurate as possible I need to make sure, firstly, 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 may effect the resistance, also. The reading that we take of the voltage should be done fairly promptly after the circuit is connected.

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Most errors in my experiment were encountered in the measuring of the wire. This is because it simply was not very practical to hold a piece of wire straight, whilst holding it next to a ruler and then trying to accurately fix crocodile clips to the right part on the wire. Also I do not feel that the crocodile clips were always fixed securely to the wire. This also meant that they were easy to move about on the wire changing the length of it. Errors rarely occurred in the setting of the current and the reading of the voltage.. Another example of this is the wire was never totally straight when I started the experiment, which may also, as said earlier on, effect the resistance of it.

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