Calculate the magnetic flux density in air at a point 15mm from a long straight wire carrying a current of 100A

Answer 1

B = (mu-o)*I/(2*pi*R) Tesla, where

mu_o = 4 pi*10^-7 Weber/Amp*meter
I = 100 A
R = 0.015 m
= 2*10^-7*100/0.015 = 0.00133 T

The free space permeability, mu_o, can be used for air