Resistance of a Wire.

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Physics Investigation – Resistance of a Wire        Astrid Christie

Planning

Prediction: 

The resistance of a wire depends on a number of variables:

1) The length of the wire,
2) The cross sectional area of the wire,

3) The material the wire is made out of,
4) The temperature of the wire.

I shall be investigating the second variable, the cross-sectional area of the wire.

I predict that as the cross-sectional area of a wire increases, the resistance of the wire decreases, and vise versa.

                                Resistivity, ρ (ohm metres) x length, l (metres)

Resistance, R (ohms) =         Cross-sectional area, A (square metres)

(“Advanced Physics For You”, pgs 196 – 197)

Scientific Reason: In an experiment in which the length of the wire is increased (in which the resistance also increases), this does not create any more space in which the free electrons can move (as the cross sectional area stays the same, but since there is more wire, there are more free electrons). However, in this experiment, there is a greater area in which the free electrons can move, and therefore they collide less frequently with atoms, therefore, less resistance is produced.

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My theory is that if you increase the length of the wire, there are more free electrons, but the electrons have less space to move in, so thy collide more often with the atoms, creating more resistance.

However, if you increase the cross sectional area, there are still more free electrons, but there is more room for them to move, therefore decreasing the collisions with the atoms, and in turn decreasing the resistance. This is my reason for my aforementioned prediction.

Method:  To keep the experiment as fair as possible, the ...

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