---
title: "Meaning of relative permeability"
subject: "Electromagnetism"
chapter: 3
key: "semester_3/electromagnetism:relative-permeability-indicate"
source: https://www.bctengineer.com/q/semester_3/electromagnetism/relative-permeability-indicate
site: BCT Engineering
---

# Meaning of relative permeability

Electromagnetism · Chapter 3: Magnetic field

- Asked in: 2067 Shrawan, 1 marks
- Video: [What is Permeability ? Easiest Explanation](https://www.youtube.com/watch?v=NFVGWABEZhg) — Gaurav J - TheElectricalGuy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/electromagnetism/relative-permeability-indicate
- Whole chapter: https://www.bctengineer.com/md/semester_3/electromagnetism/chapter-3

## Question

What does the relative permeability of a substance indicate?

## Short answer

Relative permeability μ_r = μ/μ₀ = 1+χ_m indicates how many times the flux density in a material exceeds that in free space for the same applied H, measuring the ease of magnetization; it is near 1 for non-magnetic substances and much larger for ferromagnets.

## Answer

Relative permeability μ_r = μ/μ₀ = 1 + χ_m tells how many times the magnetic flux density in a material is greater than in free space for the same magnetising field H. It indicates how easily the material can be magnetised: μ_r ≈ 1 for non-magnetic and para/diamagnetic materials, and μ_r ≫ 1 (hundreds to thousands) for ferromagnetic materials such as iron.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Relative permeability mu_r indicates:
   A. How many times B in the material exceeds B in free space for the same H
   B. The conductivity of the material
   C. The electric permittivity
   D. The speed of light in the material
   Answer: A. mu_r = mu/mu0 compares the flux density in the material with that in free space for the same H. (Key point: Meaning)

2. Which relation holds?
   A. mu_r = chi_m
   B. mu_r = 1 - chi_m
   C. mu_r = 1 + chi_m
   D. mu_r = 1/chi_m
   Answer: C. mu_r = 1 + chi_m. (Key point: Relation to susceptibility)

3. Which materials have mu_r much greater than 1?
   A. Diamagnetic materials
   B. Free space
   C. Ferromagnetic materials such as iron
   D. Air and copper
   Answer: C. Ferromagnetic materials have mu_r in the hundreds to thousands, while non-magnetic and para/diamagnetic ones are close to 1. (Key point: Typical values)

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