A thin but long, hollow, cylindrical tube of radius r carries a current i along its length. Find the magnitude of the magnetic field at a distance r/2 from the surface (a) inside the tube (b) outside the tube.

Explanation

(a) Magnetic field inside the tube = 0
[since magnetic field inside I any
conducting fube is zero.]
(b) The point outside the tube with
distance `(r )/(2)`
Then net distacne from centre
`= r+(r )/(2) = (3r)/(2)`
So, net magnetic field `=(mu_oi)/(2pi(3r)/(2)= (mu_oi)/(3pir).`