The distance between two consecutive crests in a wave is known as:

$(a)$ The sound of an explosion on the surface of a lake is heard by a boatman $100 \ m$ away and a diver $100 \ m$ below the point of explosion. Of the two persons mentioned (boatman or diver),who would hear the sound first and why?
$(b)$ Calculate the wavelength of a sound wave whose frequency is $220 \ Hz$ and speed is $440 \ m \ s^{-1}$ in a given medium.

How do our ears permit us to receive sound?

The stem of a tuning fork is pressed against a table top. Answer the following questions: $(i)$ Would the above action produce any audible sound? $(ii)$ Does the above action cause the table to set into vibrations? $(iii)$ If the answer above is yes,what type of vibrations are they? $(iv)$ Under what conditions does the above action lead to resonance?

What do you understand by the term echo?

What is a transverse wave?