A long solenoid is fabricated by closely winding a wire of radius
Question:

A long solenoid is fabricated by closely winding a wire of radius $0.5 \mathrm{~mm}$ over a cylindrical nonmagnetic frame so that the successive turns nearly touch each other. What would be the magnetic field $B$ at the center of the solenoid if it carries a current of $5 \mathrm{~A}$ ?

Solution: