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A linearly polarized electromagnetic wave given as E = E0 \hat{i} cos (kz – ωt) is incident normally on a perfectly reflecting infinite wall at z = a. Assuming that the material of the wall is optically inactive, the reflected wave will be given as [NCERT Exemplar] (a) Er = -E0 \hat{i} cos (kz – ωt). (b) Er = E0 \hat{i} cos (kz + ωt). (c) Er = -E0 \hat{i} cos (kz + ωt). (d) Er = E0 \hat{i} sin (kz – ωt). |
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Answer» When a WAVE is reflected from DENSER medium, the reflected wave is without CHANGE in TYPE of wave but with a change in phase by 180∘ or π radian. THEREFORE, for the reflected wave we use z=−z,iˆ=−iˆ and additional phase of π in the incident wave. The incident em wave is, E=E0iˆcos(kz−ωt) The reflected em wave is Er=E0(−iˆ)cos[k(−z)−ωt+π]=−E0iˆcos[−(kz−ωt)+π] =E0iˆcos[−(kz−ωt)][∵cos(θ+π)=−cosθ] =E0iˆcos(kz+ωt)[∵cos(−θ)=cosθ] |
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