Question

Radio waves from a star, of wavelength 228 m, reach a radio telescope by two separate paths, as shown in the figure below (not drawn to scale). One is a direct path to the receiver, which is situated on the edge of a cliff by the ocean. The second is by reflection off the water. The first minimum of destructive interference occurs when the star is theta = 26.0 degree above the horizon. Find the height of the cliff. (Assume no phase change on reflection. The image is not drawn to scale; assume that the height of the radio telescope is negligible compare to the height of the cliff.) Your response differs from the correct answer by more than 10%. Double check your calculations, m

Answer 1

26degree
Δ=λ2-λ1=λ(1-sinα)

if the first minimum(Δ=λ/2)
occur when θ=26,then
α=180-(θ+90+θ)=90
λ2=Δ/1-sinα
=(228/2)/1-sin90
=319.2
h=λ2sin26

=319.2sin26=139.92
=139.92

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