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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.
Don't you figure that there is a conservation of mass?R=rho*l / A
I just don't get the part how the length of the wire affects the cross sectional area/radius.
Consider that your cross sectional area is the cross section of a thin shelled tube.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.
I tried:
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
It's an insulating rod, so only the surface foil conducts.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?