Question: As weve seen, Eq. (7.33) describes the beat pattern. Lets now derive a different version of that expression assuming that the two overlapping equal-amplitude cosine

As we€™ve seen, Eq. (7.33) describes the beat pattern. Let€™s now derive a different version of that expression assuming that the two overlapping equal-amplitude cosine waves have angular spatial frequencies of kc+ Δk and kc- Δk, and angular temporal frequencies of ωc+ Δω and ωc- Δω, respectively. Here kcand ωccorrespond to the central frequencies. Show that the resultant wave is then

E = 2E01 cos (Akx – Awt) cos (kx – w.t)

Figure P.7.19 (a) E Eo --Eo (b) х

Explain how each term relates back to
E = 2E01 cos (Akx Awt) cos (kx w.t) Figure P.7.19 (a)Prove that the speed of the envelope, which is the wavelength of the envelope divided by the period of the envelope, equals the group velocity, namely, Δω/Δk.

E = 2E01 cos (Akx Awt) cos (kx w.t) Figure P.7.19 (a) E Eo --Eo (b)

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