Question

if 18 meters of high resistance wire with a diameter of 1.2 mm has a resistance of 10 ohms, what is the resistance of 27 m of the same type of wire with a diameter of 1.5mm?

Answer 1

The electrical resistance of a wire varies as its length and inversely as the square of the diameter.
R = (k*L)/(d^2)
where k = proportionality constant
Since the two wires have the same material, their proportionality constant is same.
Equating that
(R1*d1^2)/L1 = (R2*d2^2)/L2

Given that R1 = 10 ohms, d1 = 1.2 mm or 0.0012 m, L1 = 18 m, d2 = 1.5 mm or 0.0015 m, L2 = 27 m, and R2 is unknown.
Therefore
[10*(0.0012^2)]/18 = [R2*(0.0015^2)]/27
R2 = 9.6 ohms