1)

The magnetic field (B)  inside a long solenoid  having n turns per unit length and carrying current l when the iron core is kept  in it is (μ0= permeability  of vacuum, χ= magnetic susceptibility)


A) μ0nl(1χ)

B) μ0nlχ

C) μ0nl2(1+χ)

D) μ0nl(1+χ)

Answer:

Option D

Explanation:

According to question, charge in magnetic field due to insertion of iron core is given by

 B'=μ B

μ0(1+χ)B[μ=μ0(1+χ)]

where, B= magnetic field  in air 

 μ0= permeability of vacuum

 χ= magnetic susceptibility

As we know magnetic field inside the solenoid is given by B=μ0nl

So, B'= μ0(1+χ) nl