Question:
Which of the following statement is NOT correct?
Which of the following statement is NOT correct?
Show Hint
Waves above about 30 MHz are not reflected by the ionosphere; they pass through it (used for satellite communication).
Updated On: Oct 31, 2026
- Ground wave signals are more stable than the sky wave signals.
- The critical frequency of an ionospheric layer is the highest frequency that will be reflected back by the layer when it is vertically incident.
- Electromagnetic waves of frequencies higher than about 30MHz cannot penetrate the ionosphere.
- Sky wave signals in the broadcast frequency range are stronger at night than in the day time.
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The Correct Option is C
Solution and Explanation
Check each statement.
(1) Ground (surface) waves follow the earth and are not affected by ionospheric changes, so they are more stable than sky waves. Correct.
(2) Critical frequency is the highest frequency reflected by an ionospheric layer for vertical incidence. Correct (definition).
(3) Waves above about 30 MHz are not reflected but do penetrate the ionosphere; that is why satellite communication uses them. So the statement 'cannot penetrate' is wrong.
(4) At night the absorbing D layer disappears, so sky-wave signals at broadcast frequencies are stronger. Correct.
The NOT correct statement is (3).
Answer: (3) Electromagnetic waves of frequencies higher than about 30MHz cannot penetrate the ionosphere.
(1) Ground (surface) waves follow the earth and are not affected by ionospheric changes, so they are more stable than sky waves. Correct.
(2) Critical frequency is the highest frequency reflected by an ionospheric layer for vertical incidence. Correct (definition).
(3) Waves above about 30 MHz are not reflected but do penetrate the ionosphere; that is why satellite communication uses them. So the statement 'cannot penetrate' is wrong.
(4) At night the absorbing D layer disappears, so sky-wave signals at broadcast frequencies are stronger. Correct.
The NOT correct statement is (3).
Answer: (3) Electromagnetic waves of frequencies higher than about 30MHz cannot penetrate the ionosphere.
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