In SONAR, by measuring the change in the frequency between the sent signal and received signal, the speed of marine animals and submarines can be determined.

Loudness of sound depends upon the intensity (I) of sound. The intensity of sound, in turn depends on the amplitude of the sound wave.

Dolphins, dogs, bats can hear the ultrasonic vibrations.

Given: V = 331 ms^-1, λ = 0.20 m, n =?
V = n x λ
331 = n(0.20)
n = \(\frac{331}{0.20}\) = 1655 Hz

The minimum distance required to hear an echo is 1/20^th part of the magnitude of the velocity of sound in air.
i.e.  \(\frac{1}{20} \times 344 = 16.7m\)

(i) The audible range of frequency is 20 Hz to 20,000 Hz.
(ii) These are generated by vibrating bodies such as vocal cords, stretched strings, etc.

If the particles of the medium vibrate along the direction of propagation of the wave, then the waves are said to be longitudinal.

The sudden increase in pressure and temperature from lightning produces rapid expansion of the air surrounding and within a bolt of lightning. In turn, this expansion of air creates a sonic shock wave, similar to a sonic boom, which produces the sound of thunder.

Longitudinal waves travels in a medium as a series of alternate compression and rarefactions i.e., they travel as variations in pressure. So they are called pressure waves.