Question

For sky wave propagation, the radio waves must have a frequency range in between:
A. 1 MHz to 2 MHz
B. 5 MHz to 25 MHz
C. 35 MHz to 40 MHz
D. 45 MHz to 50 MHz

Answer 1

Hint: The low radio waves frequencies are transmitted using ground wave propagation. For sky wave propagation, we need higher frequencies which can travel to long distances in the atmosphere without much distortion.

Complete answer:
In sky wave propagation, the radio waves used lie between the ultra high frequencies and low frequencies. The range lies between 5 MHz to 25 MHz.

Thus, the correct answer is option B.

Additional information:
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.
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.
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.
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.

Note:
The sky wave propagation relies on the reflection of radio waves from the charged ions in the ionosphere. The charged particle absorbs the radio waves and gets to a high energy state of oscillation emitting this energy back towards earth after coming to the ground state.