The ratio of the amplitudes of the electric field and magnetic field strengths has the same dimensions as that of:

The intrinsic impedance of the wave is defined as the ratio of the electric field and the magnetic field phasor (complex amplitude), i.e.

\(η =\frac{E}{H}=\frac{j\omega \mu }{\gamma }\)

It has a unit of Ohms and is defined as the opposition offered by the medium to the propagating electromagnetic field.

For free-space, the intrinsic impedance is a real quantity, i.e.

η  = η0 = 120π

η ≈ 377 Ω

Since the unit of impedance is also Ohms, they are of the same dimensions.

Notes: 

A uniform plane wave has the following properties:

• The electric and magnetic fields are perpendicular to each other which are also perpendicular to the direction of propagation.
• They are also called as (Transverse electromagnetic wave) TEM waves.
• The ratio \(\frac{{\left| E \right|}}{{\left| H \right|}}\) for the wave is equal to the intrinsic impedance of the medium, η.