प्रतिध्वनि हुन ध्वनिको स्रोत र वस्तुको सतहबीचको दूरी कति हुनुपर्छ ?

Option A

प्रतिध्वनि (echo): The velocity of sound in dry air is approximately 343 m/s at a temperature of 25 °C. Therefore, the reflecting object must be more than 17.2m from the sound source for echo to be perceived by a person located at the source