Consider the following statements:
(A) A bar magnet cut into two pieces along its length gives two magnets, each with a north and a south pole.
(B) A current-carrying toroid has a north pole and a south pole.
(C) Iron filings sprinkled around a bar magnet gather most near its middle and least near its ends.
(D) A repulsion between two iron bars shows that both bars are magnetised.
Which of the above statements are incorrect?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (B) and (C) only
A magnetic configuration has a north and a south pole only when its source has a net magnetic moment. A bar magnet has one, and its poles sit at the two ends.
(A) A bar magnet cut into two pieces along its length gives two magnets, each with a north and a south pole. — Correct statement. Cutting a magnet either way gives two magnets. An isolated pole is never obtained.
(B) A current-carrying toroid has a north pole and a south pole. — Incorrect statement. The field of a toroid is confined inside its windings, and it has no net magnetic moment. So it has no north or south pole.
(C) Iron filings sprinkled around a bar magnet gather most near its middle and least near its ends. — Incorrect statement. The field of a bar magnet is strongest at its two ends (the poles) and weakest in the central region. So the filings gather most near the ends and least near the middle.
(D) A repulsion between two iron bars shows that both bars are magnetised. — Correct statement. An unmagnetised iron bar is always attracted by a magnet. Repulsion needs like poles, so both bars must be magnets.
NCERT (2026-27):
Example 5.1 – “(a) In either case, one gets two magnets, each with a north and south pole.”
Example 5.1 – “(c) Not necessarily. True only if the source of the field has a net non-zero magnetic moment. This is not so for a toroid or even for a straight infinite conductor.”
Example 5.1 – “… In a bar magnet the intensity of the magnetic field is the strongest at the two ends (poles) and weakest at the central region. …”
Example 5.1 – “(d) Try to bring different ends of the bars closer. A repulsive force in some situation establishes that both are magnetised. …”