Section 6.1 · Further exercises · 2 of 17
Exercise 6.1.2: A wave towards -z in a dielectric
About the further exercises of Section 6.1
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 .
A wave towards in a dielectric
#In a lossless medium with , the magnetic field of a uniform plane wave is
Find (a) the frequency, , , and the direction of propagation, (b) and , (c) the instantaneous and the time-average Poynting vector.
The plus sign in means travel towards . In a lossless medium holds at every instant, because is real.
, so . The argument is constant for decreasing in time: the wave travels towards , .
, and
points along , and .
cf. Problem 6.1.10