Question

The resistance of wire of length is 250 m is 1 ohm . If the resistivity of material of wire is 1.6× 10^-8 ohm m, find the area of cross-section of the wire. How much does the resistance change of the diameter is doubled?

Answer 1

The resistance is given as: R= PlA=> 1 1.6×10-8×250A= A = 1.6×10-8×250= 4×10-6m2A= piπ2d22
when the diameter is doubled, then
A=piπd22= piπd22=> 4piπd22= 4Ak keep the same length, the resistance of the wire.
R= PlA= 14PlA= Ru= 14= 0.25.