The magnetic field lines in the gap between two flat pole pieces of a magnet
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → bend outwards a little near the edges of the pole pieces
In the middle of the gap, the field lines are nearly straight and evenly spaced. Near the edges they spread out a little. This spreading of the lines is called fringing.
Option (1) stay perfectly straight up to the edges of the pole pieces — Incorrect. Lines that stay perfectly straight and then stop sharply at the edges would break Ampere’s law. Some bending at the edges always occurs.
Option (2) bend outwards a little near the edges of the pole pieces — Correct. The lines bulge out near the edges of the pole pieces. This fringing cannot be avoided. The same happens to electric field lines between two charged plates.
Option (3) form closed loops inside the gap, around empty space — Incorrect. A closed loop of a static magnetic field line must go round a current. No current passes through the gap, so no such loop forms there.
Option (4) cross one another near the edges of the pole pieces — Incorrect. Field lines never cross. At a crossing point the field would have two directions at once.
NCERT (2026-27):
Example 5.3 – “(g) Wrong. Magnetic field lines between two pole pieces cannot be precisely straight at the ends. Some fringing of lines is inevitable. Otherwise, Ampere’s law is violated. This is also true for electric field lines.”