Two radio antennas are 130 m apart on a north-south line.The two antennas radiate in phase at a frequency of 3.6 MHz.All radio measurements are made far from the antennas.The smallest angle,reckoned east of north from the antennas,at which constructive interference of two radio waves occurs,is closest to:

Question

Quizplus · Accepted Answer

Constructive interference occurs when the path length difference is an integral multiple of the wavelength. The smallest angle at which this occurs is when the path length difference is half a wavelength. The wavelength is c/f = 83.3 m, so the path length difference is 41.7 m. The distance between the antennas is 130 m, so the angle is sin^-1(41.7/130) = 50°.

Two Radio Antennas Are 130 M Apart on a North-South