Which of the following are used to study the growth of fetus inside the mother's womb?

The frequencies of four sound waves are given below. Which of these sound waves can be used to measure the depth of sea?

Which of the following frequency of sound can be generated by a vibrating simple pendulum as well as by the vibrating vocal cords of a rhinoceros?

We can distinguish between the musical sounds produced by different singers on the basis of the characteristic of sound called:

The maximum speed of vibrations which produce audible sound will be in: