A wire has uniform cross sectional and resistance R. Then the wire is pulled so that the length increases by 10%. How to find the new resistance? Assumption: The wire thins uniformly.
R=rho*l / A
I just don't get the part how the length of the wire affects the cross sectional area/radius.
I got it. I thought the increase of L decrease the r to r/1.1.
Can I ask another question about resistance?
A square carbon film of thickness 5x10^-7m, rho 4x10^-5 ohm m is formed on an insulator rod of diameter 3mm.What is the length of the rod so that the carbon film on its curve surface has a resistance of 100 ohm.
RA/rho = L
100[3.142*(1.5mm+5x10^-7)^2]/4x10^-7 = L
But the answer is 1.18cm which is different from mine. Where did it gone wrong
I'm sorry but according to your equation, I don't get the answer which is 1.18cm. By the way, I also don't understand the statement "carbon film on its curve surface" means. Do you mind explaining it?