Choose the correct statements:
A. Diamagnetic substances have non zero resultant magnetic moment.
B. The magnetisation of a paramagnetic material is inversely proportional to the absolute temperature T.
C. At high enough temperature, a ferromagnet becomes a paramagnet.
D. Magnetic permeability of ferromagnets, \( \mu \gg 1 \)
E. Susceptibility of Diamagnetic, \( \chi \gg 1 \)
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → B, C & D only
Magnetic materials are grouped by their susceptibility \( \chi \): small and negative for diamagnetic, small and positive for paramagnetic, and very large and positive for ferromagnetic substances.
(A) Diamagnetic substances have non zero resultant magnetic moment. — Incorrect. In a diamagnetic atom the electron moments cancel, so the resultant magnetic moment is zero; a moment appears only while a field is applied, and it opposes the field.
(B) The magnetisation of a paramagnetic material is inversely proportional to the absolute temperature T. — Correct. This is Curie’s law: for a given field, thermal agitation disturbs the alignment of the atomic dipoles more at higher temperature.
\( \displaystyle M = C\,\frac{B_0}{T} \)
(C) At high enough temperature, a ferromagnet becomes a paramagnet. — Correct. Above the Curie temperature the domain structure breaks up and the substance behaves as a paramagnet.
(D) Magnetic permeability of ferromagnets, \( \mu \gg 1 \) — Correct. Ferromagnets have a very large susceptibility, so their relative permeability \( \mu_r = 1 + \chi \) runs into the thousands.
(E) Susceptibility of Diamagnetic, \( \chi \gg 1 \) — Incorrect. The susceptibility of a diamagnetic substance is small and negative (of the order of \( -10^{-5} \)).
Note: Statements (A), (C), (D) and (E) of this question are from the latest textbook (2026-27). Statement (B), that the magnetisation of a paramagnetic material is inversely proportional to the absolute temperature, is printed only in the pre-rationalised textbook (2022-23). It was removed from the latest book, but the effect of temperature on magnetic properties is still in the CUET 2026 syllabus, so do not skip it.
NCERT (2026-27):
Magnetic Properties of Materials – “… In terms of the susceptibility χ, a material is diamagnetic if χ is negative, para- if χ is positive and small, and ferro- if χ is large and positive.”
Diamagnetism – “… Diamagnetic substances are the ones in which resultant magnetic moment in an atom is zero.”
Ferromagnetism – “… There are a number of elements, which are ferromagnetic: iron, cobalt, nickel, gadolinium, etc. The relative magnetic permeability is >1000! The ferromagnetic property depends on temperature. At high enough temperature, a ferromagnet becomes a paramagnet.”
NCERT (Pre-rationalised edition, 2022-23):
Paramagnetism – “… Experimentally, one finds that the magnetisation of a paramagnetic material is inversely proportional to the absolute temperature T,
\( \displaystyle M = C\,\frac{B_0}{T} \qquad [5.20(a)] \)”