A student draws the magnetic field lines of a finite current-carrying…

The correct answer is Option (4) → the field lines must curve out at both ends and meet to form closed loops

A finite solenoid behaves like a bar magnet. Its field lines come out of one end, curve round outside it and enter the other end. Straight lines that stay within the width of the solenoid at its ends would go against Ampere’s circuital law.

Option (1) a finite solenoid has no magnetic field outside it — Incorrect. Only a very long, ideal solenoid has almost no field outside. A finite solenoid acts like a bar magnet, so it has a field outside, just as a bar magnet does.

Option (2) the field lines must spread out radially from each end of the solenoid — Incorrect. Lines spreading out from an end would give a net outward flux through a closed surface around that end. The net magnetic flux through any closed surface is zero.

Option (3) inside the solenoid the field lines must be circles around its axis — Incorrect. Inside a solenoid the field is along its axis. Circles around a line belong to the field of a straight current-carrying wire.

Option (4) the field lines must curve out at both ends and meet to form closed loops — Correct. The lines leave one end, curve out, and return to the other end, so each line is a closed loop.

NCERT (2026-27):
Example 5.3 – “(d) Wrong. Field lines due to a solenoid at its ends and outside cannot be so completely straight and confined; such a thing violates Ampere’s law. The lines should curve out at both ends, and meet eventually to form closed loops.”