Give four differences between longitudinal waves and transverse waves. Represent them graphically as well.

What is an echo? Explain how the principle of echo is used by

a. bat during its flight at night and

b. a dolphin to locate small fishes as its prey. 

A sound of a certain frequency is travelling at speed of $330 \mathrm{m}/\mathrm{s}$ in a given medium. Calculate the frequency, if its wavelength is $3 \mathrm{m}$.