Question

If X stands for the magnetic susceptibility of a substance, $\mu$ stands for magnetic permeability and ${\mu _0}$ stands for the permeability of free space, then:
(A) For paramagnetic substances $X > 0,\mu = 0$
(B) For paramagnetic substance $\mu > {\mu _0},X > 0$
(C) For diamagnetic substance $X < 0,\mu < 0$
(D) For ferromagnetic substance $X < 0,\mu < {\mu _0}$

Answer 1

Hint
In this question, we need to check for the values of X, $\mu$ , and ${\mu _0}$ for all three types of substances which are paramagnetic, diamagnetic, and ferromagnetic. We will then have to compare these values with each other to find the correct option for our question.

Complete step by step solution
As we know that the relation between X and $\mu$ of a substance is given by
$X = \dfrac{\mu }{{{\mu _0}}} - 1$
In a paramagnetic substance, there are some unpaired electrons that are polarized in the presence of an external magnetic field. This means that X for paramagnetic > 0. For a diamagnetic substance, the number of paired electrons is in majority. Also, these substances are polarized in the direction opposite to the external magnetic field. This means that $X < 0$ . Ferromagnetic substances polarize strongly in the presence of an external magnetic field and thus they have high susceptibility. Using the above formula, we find that $\mu > {\mu _0}$ for a paramagnetic substance because $\dfrac{\mu }{{{\mu _0}}} - 1$ should always be greater than 0.

Therefore, the correct answer is option B.

Note:
The presence of a paired electron is what makes the diamagnetic substances resistant to the magnetic field. They are such that the magnetic field does not even pass through them like ferromagnetic and paramagnetic. It just sweeps away like water waves around a rock.