ianmiller999

I was wondering if anybody can help me, I am currently worked on an investigation about how the length of a wire affect its resistance.

I was wondering if anybody knows where I can find any formula or scientific explanations.

I have tried google but keep coming up with a load of coursework essays.

AndyC_772

iTrader: (2)

Provided the wire is uniform, then its resistance is directly proportional to its length. The formula is (something like) R=rho*L/A, where:

R = resistance (Ohms)
rho = resistivity of the material (Ohm metres)
L = length of wire (metres)
A = cross-sectional area of wire (metres).

For a round wire, A = pi*r^2 where r is the radius of the wire.

mj

http://hyperphysics.phy-astr.gsu.edu.../resis.html#c2

check the links for calcs and different values for different materials.

ajm

The resistance of a wire varies proportionaly with its length. Imagine a length of wire as a resistor, doubling the the length of the wire is the same as having two resistors in series i.e. double the resistance.

johnfelstead

R=pL/A where R=resistance p=resistivity L=length A=cross sectional area

http://hyperphysics.phy-astr.gsu.edu.../resis.html#c2

ianmiller999

cheers guys

V45DSM

If you've got a 2m length of cable with a resistance of 10 Ohms and you double the length of cable it will have a resistance of 20 Ohms. If you place the cables next to each other and twist the ends together, it will have a resistance of 5 Ohms. Ambient temperature/bends/kinks will all affect the resistance of the wire.

alcazar

iTrader: (2)

Are you doing GCSE physics? This is a VERY common piece of coursework for that.

Alcazar

ianmiller999

Yes I am I need to do some research for my SC1s but thanks to coursework.com it makes searching on google very difficult. Thanks for the link to that science site, that will be allowed as a source for my information

Thanks to our school being very "kind" they only give us revision guides rather then text books, thus there is no or little information about how length affects the resistence of a wire or how, and they only gave us two days to research so I couldnt get to the library.

Once again ScoobyNet has been very helpful, cheers guys.

TelBoy

Ian, you might also want to investigate Townshend, who make the only hi-fi speaker cable in the world (AFAIK) where the length doesn't affect its impedence. It's called Isolda. Might be worth a few extra brownie points to mention the existence of such a product. I have a contact number for them if you fancy talking to the manufacturers direct, if you can't get what you need from the web.

ianmiller999

That may get me a few brownie points with the teacher, she is into all this high quality audio products, I will take a look for there website. Cheers

ajm

Actually this is slightly misleading, the Isolda cables are constructed in fixed lengths and each length is tuned to have a set impedance by varying its conductance and capacitance. If you were to cut one in half you would upset this and it would indeed affect the impedance.

Also, impedance is only really meaningful in an AC situation, whereas resistance is a DC property.

V45DSM

Surely you mean inductance?




[Edited by V45DSM - 1/21/2004 9:13:28 PM]

j.r-xrs

http://www.purchon.com/investigations/ is a helpful site I used when writing up all of my GCSE science investigations.

Good luck

ianmiller999

Cheers

ajm

Yes thats the one! That will teach me to rely on memory alone

The point being that, as I understand it, they provide cables in set lengths but with all similar impedances. This is not the same as saying the impedance does not change with length as was suggested above.

If a company really could do that then they would be selling their cables to power companies, not to hifi boffins! Infact the only reason power is sent over cables at such a high stepped up voltage is to minimise the effects of impedance by reducing the current and hence the energy lost as heat from the wires.

mj

..or "volt drop" to us lesser mortals...

ajm

I can't see any harm in helping fulfill the goverment's claims that GCSE standards are improving!

Madjay

i did that for my physics GCSE course ach does where the days u got A's and didnt need to revise for **** all

Bubba po

Especially written English, eh, Madjay?