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Question: Answered & Verified by Expert
Assertion : Electromagnetic waves with frequencies smaller than the critical frequency of ionosphere are used for communication using sky wave propagation.
Reason : The refractive index of the ionosphere becomes very high for frequencies higher than the critical frequency.
PhysicsCommunication SystemAIIMSAIIMS 2006
Options:
  • A If both assertion and reason are true and reason is the correct explanation of the assertion
  • B If both assertion and reason are true but reason is not the correct explanation of the assertion
  • C If assertion is true, but reason is false
  • D Both assertion and reason are false statements.
Solution:
1581 Upvotes Verified Answer
The correct answer is: If both assertion and reason are true but reason is not the correct explanation of the assertion
If the frequencies of the waves are less than that of the critical frequency. They will be reflected back as the ionosphere has refractive index less than free space. This is the principle of sky wave propagation.
The statement given in the
Reason that the refractive index becomes high is correct. But the Reason given is not true for the assertion.

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