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(C) Sound waves are low-frequency waves (typically $20 \ Hz$ to $20 \ kHz$). For efficient transmission of electromagnetic waves,the antenna length sh

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They are heavily absorbed by the atmosphere.

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(C) Sound waves are low-frequency waves (typically $20 \ Hz$ to $20 \ kHz$). For efficient transmission of electromagnetic waves,the antenna length should be at least $\lambda/4$,where $\lambda$ is the wavelength. For a frequency of $15 \ kHz$,the wavelength $\lambda = c/f = (3 	imes 10^8 \ m/s) / (15 	imes 10^3 \ Hz) = 20 \ km$. The required antenna height would be $\lambda/4 = 5 \ km$,which is practically impossible to construct. Furthermore,low-frequency waves are heavily absorbed by the atmosphere. Therefore,sound waves are modulated onto high-frequency carrier waves for transmission.

Column $A$	Column $B$
$A$. $D$-layer	$I$. $250-400 \ km$
$B$. $E$-layer	$II$. $170-190 \ km$
$C$. $F_1$-layer	$III$. $95-120 \ km$
$D$. $F_2$-layer	$IV$. $65-75 \ km$

Sound waves cannot be transmitted directly after conversion into electrical waves because...

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