A long, straight wire carries a current of 60 A. The magnetic field produced by this current at a ...?

Question

A long, straight wire carries a current of 60 A. The magnetic field produced by this current at a certain point is 8.5 x 10^-5 T. How far is the point from the wire?

Answer 1

This is a simple application of Biot-Savart law for an infinitely long wire

B= u I/(2 pi R)

u= 4 pi E-7 T m^2/ A

then R= u I/(2 pi B)

R= 4 pi E-7 x 60 /( 2 pi 8.5 E-5 )

R= 2 E-7 x 60 /( 8.5 E-5 )=
R=14.1 cm