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Wave Optics — JEE physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 ScienceJEE physicsWave Optics1 Mark
Question
Assertion : Television signals are received through sky-wave propagation.
Reason : The ionosphere reflects electromagnetic waves of frequencies greater than a certain critical frequency.
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Answer

(d) In sky wave propagation, the radio waves having frequency range $2 MHz$ to $30 MHz$ are reflected back by the ionosphere. Radio waves having frequency nearly greater than $30 MHz$ penetrates the inosphere and is not reflected back by the ionosphere. The TV signal having frequency greater than 30 $MHz$ therefore cannot be propagated through sky wave propagation.In case of sky wave propagation, critical frequency is defined as the highest frequency is returned to the earth by the considered layer of the ionosphere after having sent straight to it. Above this frequency, a wave will penetrate the inosphere and is not reflected by it.

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