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Question:

Name the three different modes of propagation of electromagnetic waves. Explain, using a proper diagram the mode of propagation used in the frequency range above 40MHz.

Solution:

The three modes of propagation are-
(i) Ground waves
(ii) Space waves
(iii) Sky waves
The ionosphere acts as a reflector for certain frequencies (3Hz to 40Hz).
Above 40Hz, waves penetrate the ionosphere and escape.