The magnetic field inside a long solenoid having 50turns/cm is increased from 2.5 x 10-3T to 2.5T when an iron core of cross-sectional area 4cm2 is inserted into it. Find (a) the current in the solenoid, (b) the magnetization I of the core and (c) the pole strength developed in the core.
B1 = 2.5 × 10–3, B2 = 2.5
A = 4 × 10–4m2, n = 50turns/cm = 5000turns/m
(a) B = μ0ni,
=> 2.5 × 10–3 = 4π × 10–7 × 5000 × i
= 1.99 × 106 ≈ 2 × 106
