Let us suppose there is a block of a ferromagnetic material inside a very long ideal solenoid. We know that the magnetic field lines inside are always in a straight line which will be perpendicular to the surface of the block. Now i am confused why does the magnetic field inside the block increases? I have read that the perpendicular or the normal component of the magnetic field doesn't changes when it goes from one medium to other. Then why is it true? Am i missing something?
The field from the solenoid would cause an alignment of the atomic magnetic dipoles within the ferromagnetic material. This would be equivalent to putting a bar magnet inside the solenoid. The resultant field would be the vector sum of the two at each point. The field would not change immediately upon leaving the end of the bar, but the contribution from the bar would start to spread (and curve back around to the other end). At some distance from the bar the field of the solenoid would predominate.