Question

The magnetic field $(B)$ inside a long solenoid having $n$, turns per unit length and carrying current $I$ when iron core is kept in it is ($\mu_0 =$ permeability of vacuum, $χ =$ magnetic susceptibility)

• A. $μ_0\, nI\, (1 − χ)$
• B. $μ_0\, nIχ$
• C. $μ_0\, nI^2\, (1 + χ)$
• D. $μ_0 \,nI (1 + χ)$

Answer 1

Answer: (D)

Magnetic field due to solenoid $=\mu \times n \times I$
where $\mu=$ permeability
$n =$ turn density
$I =$ current
Also $\mu=\mu_{0}(1+\chi)$
where $\chi=$ magnetic susceptibility
$B _{\text {solenoid }}=\mu_{0} n I (1+\chi)$