Radio waves from a star, of wavelength 226 m, reach a radio telescope by two sep
ID: 1521516 • Letter: R
Question
Radio waves from a star, of wavelength 226 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 ? = 30.0° 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.)
? m.
Explanation / Answer
d = d2 -d1 = d2*(1-sinalpha)
d = lambda/2 when theta - 30
alpha = 180 - (theta + 90 + theta ) = 30
d2 = d/(1- sinalpha)
d2 = (226/2)/(1-sin30 ) = 226
h = d2*sin30
= 226*sin30 = 113 m
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