# Resistance - Physics Coursework?

I've got to do some coursework on the resistance of a wire and if the length of the wire affects the resistance. I need to explain why the longer the wire the bigger the resistance is? I know it is because of the amount of collisions, but could you help me in understanding what exactly happens during the collisions and how it affects the resistance?

Thanks

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• Anonymous

For what level is this coursework?

The relationship between resistance and the length of a wire has been a GCSE "favourite" for years.

At GCSE, I would happily accept that the increase in resistance is due to increased collisions - I wouldn't expect any more.

But, I would like an explanation of metals conducting because they have free electrons, so they are basically metal ions surrounded by free electrons.

And I think I'd like be told that one can assume an equal number of ions per cm of wire, so every increase in length of 1 cm should give an equal increase in collisions and thus an equal increase in resistance.

Hence resistance is directly proportional to length.

If you want more detail, you are going beyond GCSE level - and you can't get more than 100% !

• If a short wire has a resistance of say x then by doubling the length of the same wire the resultant resistance is 2x. I have ot heard of this explained in terms of collisions before but would assume that in a high resistance wire the number of collisions occurring is high therefore the resultant current flow is low i.e. a high resistance. I would recommend looking at wikipedia (www.wikipedia.org) for a more detailed description.

• the electrons that flow (to make the current) hit the atoms or other electrons in the metal and loose energy due to the collision.

Resistance is basically telling you how many collisions there are going to be (I don't mean that electrons travelling through a 3 ohm resistor will have 3 collisions).

The longer the wire, the higher probability of there being more collisions --> higher resistance.

Hope that helps =]

• Anonymous

if you have a wire with a resistance of 50 ohms per foot,a wire that is 5 feet long has a resistance of 5'x50 ohms or 250 ohms.

• Did you know that voltage is really potential energy per charge?

V = P.E/q

in joules/coulomb.

To move a 1 coulomb charge against its normal flow, we have to do work on it, if this amount is one joule, then we say the potential difference is one joule/coulomb, or 1V. But P. Diff. indicicates that the voltage at the second point must be zero. When you release that charge, it will revert to flow back in the normal cycle, where the potential electrical energy is turned into kinetic energy, which is lost when the charge stops.

Using parallel plates will help. Say you have a + ve 1 C charge and you lift it from - ve plate to top of +ve plate, using 1J of energy. When held at the top , this charge will have high potential energy of 1J.

Release it, that energy changes to kinetic energy is used and the voltage at the end has low potential (i.e 0) the P. diff. is therefore (1-0) which is one volt worth.

So travelling along a circuit, the energy in a conventional current flows from + ve to - ve, where + ve has high potential and -ve has low potential. Potential energy of the charge, i.e voltage will be lost as the current flows towards the low potential.

This is another avenue to look at it. I dunno if this will help.

• yet yet another religious nut thinking atheists have particularly heard of this e book of pages. because of the fact the only place i've got heard of it particularly is from 2 posts at here from Christians speaking approximately it like anybody particularly cares.