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factors affecting resistance of a wire

Asked by im stuck | Aug 13, 2004 | GCSE Level > Physics > Coursework
im stuck
im stuck asks:

I'm really stuck on what to write for my method as I'm investigating the potenial difference and what happens to the resistance when it is increased, could you please help me?
thanks, sarah


etutor answers:

The scientific knowledge you need is basically this:

Current is caused by the flow of electrons. Particles in the wire impede the flow of electrons - this is what 'resistance' is. The longer the wire is, the more particles the electrons have to pass through, so the current is slowed down more, and the resistance will be higher.

Current is the flow of free electrons through a wire. The atoms in the wire tend to block this flow.This is resistance. Various factors affect the resistance.

Length of wire - the longer the wire is, the more collisions there are between the eelctrons and the atoms - so resistance increases.
Thickness of a wire - thin wire means less spces for electrons to pass, so higher resistance.
Material of wire - wires of different densities will block more or less electrons
Temperature - the vibration of warm molecules makes them more likely to collide with electrons, and resistance increases with temperature.

In general the resistance of a given length of conductor is inversely proportional to its cross-sectional area.
Apart from the effect of temperature the only other factor that influences the resistance is the nature of the material.
Hence,

Resistance of a wire = length of wire multiplied by a constant for a given material all divided by, Cross-sectional area

i.e. R = L/a × p ohms
where R is resistance, L is length of wire, a is cross-sectional area and p represents the constant.
It can therefore be seen that resistance increases with wire length.

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