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A substance whose permeability is more than the permeability of free space is?

A) Diamagnetic

B) Paramagnetic

C) Ferromagnetic

D) Both paramagnetic and ferromagnetic

Correct Answer

⚙️ TE • Technical Concept & PrincipleElectricalMachine

Option D

Both paramagnetic and ferromagnetic

Quick Summary:

Magnetic permeability ( $\mu$ ) measures a material's ability to support the formation of a magnetic field within itself relative to free space ( $\mu_0$ ). A material has a permeability greater than free space ( $\mu > \mu_0$ or relative permeability $\mu_r > 1$ ) if it is magnetized in the direction of an applied magnetic field, which is true for both paramagnetic and ferromagnetic materials.

⚙️TETechnical SolutionConcept & Principle

💡 Explanation

🔢 Key Formulas

$\mu = \mu_0 \mu_r$ — Permeability of a medium

$\mu_r = \frac{\mu}{\mu_0}$ — Relative permeability of a material

$\chi_m = \mu_r - 1$ — Magnetic susceptibility

⚙️ Working Principle

In paramagnetic materials, atomic magnetic dipoles align weakly in the direction of the applied magnetic field, resulting in a relative permeability slightly greater than 1 ( $\mu_r > 1$ ). In ferromagnetic materials, permanent magnetic domains align strongly with the applied field, resulting in a relative permeability much greater than 1 ( $\mu_r \gg 1$ ). Diamagnetic materials, on the other hand, weakly oppose the applied field, leading to $\mu_r < 1$ .

📌 Key Points

▸
For Diamagnetic materials: $\mu_r < 1$ and susceptibility $\chi_m < 0$ .
▸
For Paramagnetic materials: $\mu_r > 1$ (slightly) and susceptibility $\chi_m > 0$ (small positive).
▸
For Ferromagnetic materials: $\mu_r \gg 1$ (typically $10°2$ to $10°6$ ) and susceptibility $\chi_m \gg 0$ (large positive).

🛠️ Applications / Uses

▸
Ferromagnetic materials are used in core design for transformers, electrical motors, and generators.
▸
Paramagnetic and diamagnetic classifications aid in material identification and scientific sensing applications.

🔄 Comparison Table

Feature	Paramagnetic Materials	Ferromagnetic Materials
Relative Permeability ( $\mu$ _r)	Slightly greater than 1 ( $\mu$ _r > 1)	Much greater than 1 ( $\mu$ _r \gg 1)
Magnetic Susceptibility ($chi_{m}$)	Small and positive	Large and positive
Behavior in Magnetic Field	Weakly attracted to magnetic fields	Strongly attracted to magnetic fields

📄 Additional Information

▸
Option A is incorrect because diamagnetic materials have a magnetic permeability less than free space ( $\mu_r < 1$ ).
▸
Option B and C are partially correct on their own, but Option D is the complete and accurate choice as both classes satisfy $\mu > \mu_0$ .

📊 Diagram / Illustration

✅

D is correct — Both paramagnetic and ferromagnetic substances possess a permeability greater than the permeability of free space ( $\mu_r > 1$ ).

Core Concepts Used

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Magnetic Permeability Relative Permeability Magnetic Material Classification

💡 EXAM TIP

Always check if multiple options satisfy a inequality condition like $\mu_r > 1$ ; paramagnetic and ferromagnetic materials both share $\mu_r > 1$ , while diamagnetic materials have $\mu_r < 1$ .

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