What are infrasonic and ultrasonic waves? Give examples.
Infrasonic waves: If the frequency of the waves is less than 20 Hz then the waves are called infrasonic waves. Infrasonic waves are produced by large vibrating bodies.
The waves produced before the actual shockwaves during an earthquake is infrasonic waves. Animals ike whales and elephants produce infrasonic waves. Human beings cannot hear these waves.
Ultrasonic waves: When the frequency of the waves is greater than 20,000 Hz they are called ultrasonuic waves.
Bats, dogs, rats, cats, birds and insects can produce and also hear these waves.
A stone is dropped into a well, 44.1 metres deep. The sound of the splash is heard 3.13 seconds after the stone is dropped. Find the velocity of sound in air.
First we calculate time t taken by the stone to reach the water level in the well by using the relation,
A child hears an echo from a cliff 4 seconds after the sound from a powerful cracker is produced. How far away is the cliff from the child?
Why are the ceilings of concerts halls curved?
The ceilings of the concert halls are made curved so that sound after reflecting from the ceiling reaches all corners of the hall, as shown in Fig.
.
A person clapped his hands near a cliff and heard the echo after 5 s. What is the distance of the cliff from the person if the speed of the sound, v is taken as 342 ms–1?
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