Consider the following statements about magnetic materials:
(A) The susceptibility \(\chi\), the relative permeability \(\mu_r\) and the permeability \(\mu\) of a material are related, so only one of them is independent.
(B) For a paramagnetic material, \(1\lt\mu_r\lt 1+\varepsilon\), where \(\varepsilon\) is a small positive number.
(C) For a ferromagnetic material, \(\mu\gg\mu_0\).
(D) For a paramagnetic material, the susceptibility does not depend on temperature.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B) and (C) only
Materials are grouped by the sign and size of the susceptibility \( \chi \). Since \( \mu_r=1+\chi \) and \( \mu=\mu_0\mu_r \), each range of \( \chi \) gives a range of \( \mu_r \) and \( \mu \).
(A) The susceptibility \( \chi \), the relative permeability \( \mu_r \) and the permeability \( \mu \) of a material are related, so only one of them is independent. — True. The two relations above link all three. So if we know any one of them, we can find the other two.
(B) For a paramagnetic material, \( 1\lt\mu_r\lt 1+\varepsilon \), where \( \varepsilon \) is a small positive number. — True. For a paramagnet \( \chi \) is small and positive, so \( \mu_r=1+\chi \) is just above 1.
(C) For a ferromagnetic material, \( \mu\gg\mu_0 \). — True. Here \( \chi\gg1 \), so \( \mu_r\gg1 \) and \( \mu=\mu_0\mu_r \) is far larger than \( \mu_0 \).
(D) For a paramagnetic material, the susceptibility does not depend on temperature. — False. The susceptibility of a paramagnet depends on the material and also on its temperature. Lowering the temperature increases the magnetisation.
NCERT (2026-27):
Magnetisation and Magnetic Intensity – “The three quantities χ, μr and μ are interrelated and only one of them is independent. Given one, the other two may be easily determined.”
Paramagnetism – “… For a paramagnetic material both χ and μr depend not only on the material, but also (in a simple fashion) on the sample temperature. …”
Magnetic Properties of Materials – “A glance at Table 5.2 gives one a better feeling for these materials. Here ε is a small positive number introduced to quantify paramagnetic materials. …”
