Identify the correct statements in the context of paramagnetic substances.
(A) In external magnetic field B, individual atomic dipole moment points in opposite direction of B.
(B) Susceptibility is small and positive.
(C) In non-uniform magnetic field, the paramagnetic bar will tend to move from weak field to strong.
(D) Examples of paramagnetic substances are Aluminium, Sodium and oxygen.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (B), (C) and (D) only
In a paramagnetic substance each atom has a permanent magnetic moment. An external field tends to align these moments along the field, so the substance is weakly magnetised in the direction of the field.
(A) In external magnetic field B, individual atomic dipole moment points in opposite direction of B. — Incorrect. They tend to line up along B. Moments induced opposite to B are the mark of a diamagnetic substance.
(B) Susceptibility is small and positive. — Correct. The magnetisation is along the field but weak, because thermal agitation disturbs the alignment; typically \( \chi \sim 10^{-5} \) to \( 10^{-3} \).
(C) In non-uniform magnetic field, the paramagnetic bar will tend to move from weak field to strong. — Correct. Being magnetised along the field, it is attracted towards the region of stronger field.
(D) Examples of paramagnetic substances are Aluminium, Sodium and oxygen. — Correct. These are standard examples of paramagnetic materials.
NCERT (2026-27):
Magnetisation and Magnetic Intensity – “… χ is small and positive for materials, which are called paramagnetic.”
Paramagnetism – “… In the presence of an external field B0, which is strong enough, and at low temperatures, the individual atomic dipole moment can be made to align and point in the same direction as B0. … When placed in a non-uniform magnetic field, the bar will tend to move from weak field to strong. Some paramagnetic materials are aluminium, sodium, calcium, oxygen (at STP) and copper chloride.”