An audio signal of 15kHz frequency cannot be transmitted over long distances without modulation because (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
Correct options are A) , B) and D) Frequency of audio signal vm−15kHz −15×103 Hz λm=vmc=10×1033×103=0.2×105m Size of antenna h=4λ=420000=5000m Size of antenna = 5 km Audio frequency signal are of low frequency waves. So the audio wave cannot be transmitted by sky wave as they are absorbed by atmosphere. If the size of the antenna is less than 5 km, the effective power transmission would be very low because of the deviation from resonance of wavelength of wave and antenna length.
