Section 5.6 · Problems · 9 of 14
Problem 5.6.9: Two components, one medium
Two components, one medium
#The electric field of a time-harmonic wave in a nonmagnetic material is given by
Find the wavelength and the relative permittivity of the medium.
Adapted from: M. N. O. Sadiku, Elements of Electromagnetics, Problem 10.17.
Two components with different time functions (a sine and a cosine) and different amplitudes. Ask what they have in common: one and one . These fix and, for a lossless nonmagnetic medium, .
Write both components as cosines:
Both have the same and the same . The argument means travel towards , and there is no factor : the medium is lossless. The phasor is .
The phase grows by over one wavelength:
Lossless () and nonmagnetic ():
, the same as . In free space a wave is long, here it is times shorter.
The different amplitudes and phases of the two components do not change or : they decide the polarisation of the wave (Section 6.1). At , , and the tip of runs round an ellipse with semi-axes and once per period , from towards (Figure 5.6.21a). In space both components repeat every and are a quarter wavelength apart: is shifted by (Figure 5.6.21b).