Section 6.1 · Further exercises · 1 of 17
Exercise 6.1.1: Identifying a dielectric from its wavelength
Seventeen further exercises in the spirit of the problems, the home exercises and the worked examples, graded from easy to harder within each group. Exercises 6.1.1–6.1.4 are about uniform plane waves, , , and the triad, Exercises 6.1.5–6.1.6 about power, energy and loss, Exercises 6.1.7–6.1.10 about polarisation, Exercises 6.1.11–6.1.12 about the Doppler effect, and Exercises 6.1.13–6.1.17 mix power, exposure and polarisation. Besides the relations listed at the head of this subsection they use the lossy forms , , and (Exercise 6.1.6 only), the average energy density , Faraday's law , and the polarisation match . A field factor is .
Identifying a dielectric from its wavelength
#A uniform plane wave of frequency travels in a lossless, non-magnetic dielectric. Its wavelength is measured as and its electric field amplitude as . Find (a) the phase velocity and the relative permittivity, (b) the phase constant and the intrinsic impedance, (c) the amplitude of and the time-average power density. (d) How long would the wavelength be in air?
and, for , and .
, and
, that is times longer.
. is polyethylene or a PTFE-like material, the dielectric of many coaxial cables: a signal in such a cable travels at two thirds of , and the same field carries times more power density than in air because is times smaller.
cf. Problem 6.1.6