Question

A copper wire of resistivity 1.6 ×10^-8ohm metre has a cross sectional area of 20×10^-4cm². Calculate the length of the wire required to make a 10 ohm coil.

Answer 1

here
rho,(resistivity) = 1.6×10^-8

area = 20×10^-4cm2

= 20*10^-8 m2

r,resistance = 10

length,l = ?

we use formulae

r = (rho ×l) / a

10 = (1.6 ×10^-8 ×l) / 20×10^-8

(on dividing 1.6×10^-8 by 20×10^-8 we get = 0.08)

10 = 0.08 × l

l×0.08 = 10

l= 10/0.08

l = 1000/ 8

l = 125m

thus required length of wire is 125 m