Question

Frequencies in the UHF range normally propagate by means of
A. Ground waves
B. Sky waves
C. Surface waves
D. Space waves

Answer 1

Hint: The communication waves of different frequencies can be sent from one place to another in three different ways which depend on the altitude. Higher frequencies are able to travel longer distances through the atmosphere while lower frequencies are preferred for line of sight communication.

Complete step by step answer:
Long distance communication is necessary for connecting different parts of the world. The transmission of information from one place to another is done via electromagnetic waves mainly radio waves. There are three ways through which long distance communication has been made possible.

(i)Ground wave propagation: It is also called surface wave propagation. The radio waves travel near the surface of earth but this method is not useful for too long distances. Surface waves also come under this category and travel near the surface of earth.
(ii)Sky wave propagation: The radio waves sent into the higher layers of atmosphere which reflects the waves back towards earth covering a larger distance than ground waves.
(iii)Space wave propagation: The radio waves are sent beyond the atmosphere towards the satellites revolving around earth which reflect the waves back over longer distances.

The ultra-high frequencies have very large frequencies which can neither be reflected by the ions in the ionosphere or can travel near ground. Due to this, the UHFs are transmitted through space wave communication where we use satellites for reflecting waves back to earth.
Hence, the correct answer is option D.

Note:
The ionosphere ions can only vibrate at a certain range of frequencies and hence are not suitable for frequency range 3MHz to 30MHz. In case of ground waves, the high frequencies are easily absorbed by ground so ground wave propagation is also not suitable.