An audio signal of 15 kHz frequency cannot be transmitted over long distance without modulation because.

Options

A. the size of the required antenna would be at least 5 km which is not convenient
B. the audio signal can not be transmitted through sky waves
C. the size of the required antenna would be at least 20 km, which is not convenient
D. effective power transmitted would be very low, if the size of the antenna is less than 5 km

Answer

A, B, D

Explanation

Given, frequency of the wave to be transmitted is
`v_(m) = 15 kHz = 15 xx 10^(3) Hz`
wavelength `lambda_(m) = (c )/(v_(m))=(3xx10^(8))/(15xx10^(3))=(1)/(5)xx10^(5)m`
Size of the antenna required, `l=(lambda)/(4)=(1)/(4)xx((1)/(5)xx10^(5))`
`=5xx10^(3)m=5km`
The audio signals are of low frequency waves. Thus, they cannot be transmitted through sky waves as they are obsorbed by atmosphere.
If the size of the antenna is less than 5 km, the effective power transmission would be very low because fo deviation from resonance wavelength of wave and antenna length.