question_answer 18)

    An audio signal of 15 kHz frequency can not 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 5km

Answer:

      (a,b,d) Here, Size of the antenna required, The audio signals are of low frequency waves. They cannot be transmitted through sky waves 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 1 of deviation from resonance wavelength of wave and antenna length.