Which statement about μ is correct?

Which statement about μ is correct?

• A. μ = μ0
• B. μ = μr
• C. μ = μ0 / μr
• D. μ = μ0 μr

Answer: (D)

Magnetic permeability μ relates magnetic flux density B to the magnetic field intensity H through B = μ H. The quantity μ0 is the permeability of free space, and μr (a dimensionless number) is the relative permeability of the material, describing how much the material increases or decreases flux compared with vacuum. By definition, μ equals μ0 times μr, so the absolute permeability of a material is μ = μ0 μr. This means the vacuum has μ = μ0 (since μr for vacuum is 1), and any material with μr different from 1 will have a corresponding μ that is larger or smaller than μ0 accordingly. The other forms miss the correct relationship: μ equal to μ0 would only apply to free space; μ equal to μr would mix a dimensional quantity with a dimensionless one; μ equal to μ0 divided by μr would invert the correct relationship.

Magnetic permeability μ relates magnetic flux density B to the magnetic field intensity H through B = μ H. The quantity μ0 is the permeability of free space, and μr (a dimensionless number) is the relative permeability of the material, describing how much the material increases or decreases flux compared with vacuum. By definition, μ equals μ0 times μr, so the absolute permeability of a material is μ = μ0 μr. This means the vacuum has μ = μ0 (since μr for vacuum is 1), and any material with μr different from 1 will have a corresponding μ that is larger or smaller than μ0 accordingly. The other forms miss the correct relationship: μ equal to μ0 would only apply to free space; μ equal to μr would mix a dimensional quantity with a dimensionless one; μ equal to μ0 divided by μr would invert the correct relationship.