Question

Which of the following is true regarding dimagnetic substances (symbols have their usual meaning)?

• A. ${\mu }_r>1,{\chi }_m>1$
• B. ${\mu }_r>1,{\chi }_m<1$
• C. ${\mu }_r<1,{\chi }_m<0$
• D. ${\mu }_r<1,{\chi }_m>0$

Answer 1

The correct option is C ${\mu }_r<1,{\chi }_m<0$

Diamagnetic substances induce magnetic field in the direction opposite to an external applied magnetic field and thus are repelled by external applied magnetic field.

Magnetic susceptibility of these substances is very small and negative i.e ${\chi }_m<0$

For example:

For silicon, ${\chi }_m=-4.2\times {10}^{-6}$

From the equation, ${\mu }_r=1+{\chi }_m$

Thus, ${\chi }_m<0$ $⟹{\mu }_r<1$

Hence, such materials have magnetic permeability less than unity.