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Question Bank Sound 1. What is an echo? Ans. The phenomenon due to which the repetition of sound is heard, after reflection from a distant object (such as high building or hillock), after the original sound from a given source dies off, is called an echo. 2. State three conditions for the formation of echo. Ans. 1. The minimum distance between the source of sound and reflecting body should be 17 m. 2. The wavelength of sound should be less than the height of reflecting body. 3. The intensity of sound should be sufficient, so that it could be heard after reflection. 3. Derive a relation between speed of sound, distance of the source of sound from a reflecting body and the time for hearing an echo. Ans. Let v be the velocity of sound, t the time after which an echo is heard and d the distance between source of sound and reflecting body. Total distance travelled by sound before an echo is heard = (d + d) = 2d. In time t, distance travelled by sound = 2d. Class-X 1 Question Bank
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