Question

A metal wire has diameter of 0.25 mm and electrical resistivity of 0.8×10^-8 ohm metre.
(i) what will be the length of this way wire to make a resistance 5 Ohm?
(ii) how much will the resistance change, if the diameter of the wire is doubled?

Answer 1

We know that R=rho*(l/A) Therefore,l=R*A/rho l=30.66m Therefore,length of the wire = 30.66m If the diameter of the wire is doubled, new diameter=2×0.25=0.5mm=0.5*10^-3m Let new resistance be R1 R1=rho*(l/A')=rho*(l/? (2d/2) *(2d/2))=R/4 Therefore the resistance becomes 1/4th of the previous R in the given case.