Q. Two wires of same material and same length have resistances 5 and 10 respectively. Find the ratio of radii of the two wires.
R = ρl / A = ρl / πr2
R1 = ρl / A = ρl / π r12 ; R 2 = ρl / A = ρl / π r22
R2 / R1 = r12 / r22 ∴ r1 / r2 = √ R 2 / √ R 1 = √10 : √5 = √2 : 1