A radio telescope sited on the edge of a cliff overlooking the sea operates on a wavelength of 100 m. A radio star rises above the sea-side horizon and is tracked by the telescope. The first minimum of the received signal occurs when the star is 30° above the horizontal.
(a) Explain why the minimum occurs.
(b) When electromagnetic waves reflect off water they undergo a phase change of π. What does this due to the conditions for constructive and destructive interference?
(c) Determine the height of the cliff. (hint: what can be said about the orientation of the rays from the very distant star?)