Question 413955
The electrical resistance of a wire varies directly as its length and inversely as the Square of its diameter.
:
That would be: 
r = {{{L/d^2}}}
:
If a wire with length 100cm and diameter 2mm has a resistance of 1.5 Ohms,
let k = constant of variation
{{{(kL)/d^2}}} = r
 {{{(100k)/2^2}}} = 1.5
{{{(100k)/4}}} = 1.5
25k = 1.5
k = {{{1.5/25}}}
k = .06 is the constant of variation
:
 find the resistance of a wire with length 300cm and diameter 3mm.
r = {{{(.06*300)/3^2}}}
r = {{{18/9}}}
r = 2 ohms