A small compass needle is moved around a bar magnet. It is then moved around a current-carrying finite solenoid. The deflections of the needle are similar in both cases. This observation supports the idea that
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → a bar magnet may be thought of as a large number of circulating currents, like a solenoid
A compass needle shows the direction of the magnetic field at the place where it is kept. Similar deflections around the two objects mean that their field lines have the same pattern.
Option (1) a bar magnet may be thought of as a large number of circulating currents, like a solenoid — Correct. Fields of the same pattern suggest that a bar magnet acts like a solenoid. Its magnetism comes from a large number of circulating currents, as in Ampere’s hypothesis.
Option (2) a solenoid behaves like a bar magnet only when it has an iron core — Incorrect. A solenoid with no core also deflects the needle as a bar magnet does. A core only makes the field of a solenoid stronger.
Option (3) the magnetic field outside a finite solenoid is uniform, like the field inside it — Incorrect. Outside a finite solenoid, the field lines curve out of one end and return to the other end. The field there is not uniform.
Option (4) the two ends of a solenoid are isolated magnetic poles — Incorrect. Isolated magnetic poles do not exist. Cutting a solenoid gives two smaller solenoids, each with its own two ends.
NCERT (2026-27):
Bar magnet as an equivalent solenoid – “The resemblance of magnetic field lines for a bar magnet and a solenoid suggest that a bar magnet may be thought of as a large number of circulating currents in analogy with a solenoid. … One can test this analogy by moving a small compass needle in the neighbourhood of a bar magnet and a current-carrying finite solenoid and noting that the deflections of the needle are similar in both cases.”