A student went to a hill station early in the morning, he could hear the echo of his clap after 0.1 s. When he went to the same place in the afternoon he could not hear the echo at all. Explain the reason for his changed observation.
There is a rise in temperature in the afternoon, so the speed of sound increases with increase in temperature. As speed increases, time taken by reflected sound will be less, may be less than 0.1 s in afternoon. That is why the student could not hear the echo at all in the afternoon.