1) Two radio antennas are 120 m aparton a north-southline. The two antennas radi

Question

1) Two radio antennas are 120 m aparton a north-southline. The two antennas radiate in phase at a

frequency of 3.4 MHz. All radiomeasurements are made far from the antennas. The smallestangle,

reckoned east of north from theantennas, at which constructive interference of two radiowaves

occurs, is closestto:

1)

2) An FM radio transmitter, operatingat a frequency of 120 MHz, is atop a 100-mtower. An airplane

is in flight over the ocean at analtitude of 2000 m. Radio waves reach the airplane directly fromthe

transmitter and by reflection from thesurface of the ocean. When the airplane is 86 km fromthe

tower, the pilot observes that radioreception has faded due to destructive interference of thewaves

in the two paths. Assume the wavereflected from the ocean surface has undergone ahalf-wave

phase shift. In Fig. 35.1a, the wavesof the reflected path arrive at the airplane delayed, withrespect

to the direct path. The time intervalof this delay, in ns, is closest to:

2)

1) Two radio antennas are 120 m a parton a north-southline. The two antennas radiate in phase at a frequency of 3.4 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: 1) A) 38 degree B) 30 degree C) 47 degree D) 43 degree E)34 degree 2) An FM radio transmitter, operating at a frequency of 120 MHz, is atop a 100-mtower. An airplane is in flight over the ocean at analtitude of 2000 m. Radio waves reach the airplane directly fromthe transmitter and by reflection from thesurface of the ocean. When the airplane is 86 km fromthe tower, the pilot observes that radioreception has faded due to destructive interference of thewaves in the two paths. Assume the wavereflected from the ocean surface has undergone ahalf-wave phase shift. In Fig. 35.1a, the wavesof the reflected path arrive at the airplane delayed, withrespect to the direct path. The time intervalof this delay, in ns, is closest to: 2) A) 14 B) 20 C) 22 D) 16 E) 18

Explanation / Answer

separation of the two radioantennas d = 120 m frequency f = 3.4MHz                       = 3.4 * 10 ^ 6 Hz Speed of the waves   v = 3 *10 ^ 8 m / s wavelength of the waves = v / f                                                        = 88.235 m for constructiveinterference   d sin =                                                                sin = / d                                                                           = 0.735                                                                       = 47.33 degrees i.e., option ( C ) iscorrect

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