Question

A metal wire of specific resistance 64×10^-6 ohm metre and length 1.98 cm has resistance of 7 ohm find its radius

Answer 1

Sp. Resistance= 64x10^-6 ohm metre
Length L = 1.98cm = 1.98/100 metre = 1.98x 10^-2 metre
R= 7 ohm
so radius r=?

We know that R = (Sp.Resistance x L)/pie x r^2
or r^2 = (Sp.Resistance x L)/pie x R
or r^2 = (64x10^-6 x 1.98 x 10^-2 x 7) / (22 x 7)
or r^2 = 64 x 10^-8 x .09
or r = 8 x 10^-4 x 0.3 metre
or r = 2.4 x 10^-4 x 10^3 mm
or r = 0.24 mm Ans.