In a linear, isotropic magnetic material, the magnetic flux density B is related to the magnetic field strength H by which relation?

• A. B = μ H
• B. B = μ0 H
• C. B = μ_r H
• D. B = H/μ

Answer: (A)

In a linear, isotropic magnetic material, the magnetic response is proportional to the applied magnetic field. That means the magnetic flux density B is related to the magnetic field strength H by a constant of proportionality, the permeability μ of the material: B = μ H. Here μ equals μ0 μr, where μ0 is the permeability of free space and μr is the material’s relative permeability (a dimensionless number that describes how much the material increases flux compared to vacuum). In vacuum, μr is about 1, so B ≈ μ0 H.

The other forms aren’t generally correct here. B = μ0 H would only apply in vacuum. B = μr H would be missing the μ0 factor and thus would not have the correct units or scaling unless you’re explicitly using μ = μ0 μr. B = H/μ is not how B and H relate in a linear material.