Question 1156584
The electrical resistance r of a wire varies directly with its length l and inversely with the square of its diameter d. 100 m of wire with diameter 3 mm has resistance of 8 ohms. What is the resistance of 150 m of wire with diameter of 4 mm?

r{{{alpha(l/d^2)}}}

r = k*(l/d^2)

l = 100m diameter = 3mm = 0.003m , r = 8 {{{ohms}}}

k = r * d^2/l

k = 0.003^2*8/100

k= 7.2*10^-7

150m, d=0.004m, k= 2.4*10^-7

r= 7.2^-7*150 /(0.004)^2

r= 9.35 ohms