Question

The magnetic susceptibility of diamagnetic materials is:

• A. Much more than zero
• B. Less than zero
• C. Equal to zero
• D. Infinite

Hint:

Keep these susceptibility values in mind for material classification: - Diamagnetic: Small and Negative ($\chi_m < 0$) - Paramagnetic: Small and Positive ($\chi_m > 0$) - Ferromagnetic: Large and Positive ($\chi_m \gg 0$)

Answer 1

The Correct Option is B

Concept: Magnetic susceptibility ($\chi_m$) is a dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field. It is defined by the equation: \[ \vec{M} = \chi_m \vec{H} \] Where $\vec{M}$ is the magnetization vector and $\vec{H}$ is the magnetic field intensity vector. The relative permeability $\mu_r$ is related to susceptibility by: \[ \mu_r = 1 + \chi_m \]

Step 1: Analyze the physical behavior of diamagnetic materials.
When a diamagnetic material is placed in an external magnetic field, it develops an induced magnetization that opposes the applied field. This is due to the realignment of electron orbital paths according to Lenz's Law.

Step 2: Evaluate the sign of $\chi_m$.
Because the induced internal magnetic field acts in the opposite direction to the external magnetizing force vector $\vec{H}$, the scalar multiplier must be negative: \[ \chi_m < 0 \] Thus, the value is strictly negative, which means it is less than zero. This matches Option (B). Typically, for diamagnetic materials, $\chi_m$ is a very small negative value (e.g., for copper, $\chi_m \approx -9.6 \times 10^{-6}$).