A uniform magnetic field, parallel to the plane of the paper existed in space initially directed from left to right. When a bar of soft iron is placed in the field parallel to it, the lines of force passing through it will be represented by:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2)
Soft iron is a ferromagnetic material of very high permeability. Placed in a magnetic field it becomes strongly magnetised in the direction of the field, so the field inside it is much larger than outside, and the lines of force from the surroundings bend towards the bar and crowd into it, still pointing from left to right.
Why the other options are incorrect
Option (1) — Incorrect. The lines go straight through, as if the bar were not there. That would be so only for a material with no effect on the field.
Option (3) — Incorrect. The lines bend away from the bar and the field inside is weakened. This is how a diamagnetic material behaves, not soft iron.
Option (4) — Incorrect. The arrows point from right to left, opposite to the applied field, which no material can do to the net field.
NCERT (2026-27):
Ferromagnetism – “Ferromagnetic substances are those which gets strongly magnetised when placed in an external magnetic field. … Thus, in a ferromagnetic material the field lines are highly concentrated. … On the other hand, there is a class of ferromagnetic materials in which the magnetisation disappears on removal of the external field. Soft iron is one such material.”