Physics - Study Mode
[#906] Echo is heard due to
Correct Answer
(C) Reflection
Explanation
Solution: An echo is a sound that is repeated because the sound waves are reflected back.
[#907] A person standing on a railway platform listens to the whistles of arriving and departing trains. The whistle heard is
Correct Answer
(C) Of higher pitch when train arrives
Explanation
Solution: Sound is a sequence of waves of pressure that propagates through compressible media such as air or water. (Sound can propagate through solids as well, but there are additional modes of propagation). Sound that is perceptible by humans has frequencies from about 20 Hz to 20,000 Hz. In air at standard temperature and pressure, the corresponding wavelengths of sound waves range from 17 m to 17 mm. During propagation, waves can be reflected, refracted, or attenuated by the medium. Now if we consider these cases, then the train which is arriving towards us having whistles of higher pitch because it propagates through a medium which is coming towards us but the train which is leaving propagating through a medium moving further away from the listener and thus produced whistle of lower pitch.
[#908] The sound produced by a bat is–
Correct Answer
(D) Ultrasonic
Explanation
Solution: The sound waves produced by the bats are ultrasonic waves. Bats emit sounds at typically 2 or 3 times higher pitch than we can hear. Sounds above human hearing are usually called ultrasonic.
[#909] Sound is heard over longer distances on rainy days because
Correct Answer
(B) Sound travels faster in moist air
Explanation
Solution: During rainy days, the moisture content is more in the atmosphere and speed or velocity of sound increases with increase in humidity. Hence the sound travels faster on rainy days.
[#910] Which phenomenon is responsible for the echo of sound wave?
Correct Answer
(A) Reflection
Explanation
Solution: Reflection is responsible for the echo of sound wave.