An infinitely long wire with a current `I` flowing in it is located in the boundary plane between two non-conducting media with permeabilities `mu_(1)` and `mu_(2)` . Find the modulus of the magnetic induction vector thorughout the space as a function of the distance `r` from the wire. It should be horne in mind that the lines of the vector `B` are circles whose centres lie on the axis of the wire.