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