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. `12.6xx10^(-3) Wb//m^(2),6.3xx10^(-3) Wb//m^(2)`
B. `12.6xx10^(-3) Wb//m^(2),25.1xx10^(-3) Wb//m^(2)`
C. `25.1xx10^(-3) Wb//m^(2),12.6xx10^(-3) Wb//m^(2)`
D. `25.1xx10^(-5) Wb//m^(2),6.3xx10^(-5) Wb//m^(2)`

Answer

C

Explanation

`n=50/(1//100)=5000, i=4A`
`B_(c)=mu_(0)ni=4pixx10^(-7)xx5000xx4=8pixx10^(-3)`
`=8xx3.14zz10^(-3)=25.12xx10^(-3) wb//m^(2)`