A hollow cylinder having infinite length and carrying uniform current per unit length lambda along the circumference as shown

Question

A hollow cylinder having infinite length and carrying uniform current per unit length lambda along the circumference. Magnetic field inside the cylinder is:

Answer 1

Magnetic field inside the cylinder is λμ•

Explanation:

As there is given that current is flowing along its circumference. 

So we already know that inside the cylinder the magnetic field will be μ•/4π (2I'/r'), where I' is the current flowing and r' is the distance from the centre.

λ is the current per unit length so, λ = I/2πr ⇒ I = λ2πr 

Current inside the cylinder at r' distance from the centre is I' = λ2πr'

Now we put the value in the equation.
B_(inside) = μ•/4π (2I'/r') = μ•/4π (2 x λ x 2πr'/r') = λμ•