There are `50` turns of a wire in every `cm` langth of a long solenoid. If `4` ampere current is flowing in the solenoid, the approximate value of magnetic field along its axis at an internal point and at one end will be respectively

Options

A. `(mu_(0)i)/(pir)`
B. `(2mu_(0)i)/(pir)`
C. `(mu_(0)i)/(2pi r)`
D. zero

Answer

D

Explanation

According to the question `B_(1)=(mu_(0)i)/(2pi (r )/(2))` and `B_(2)=(mu_(0)i)/(2pi(r )/(2)`

so the strenght of the magnetic field at any point mid way `B_(net)=0`