(a) In a sound wave, a node is a point where the amplitude of oscillation i.e. displacement is zero as here a compression and a rarefaction meet and the pressure is maximum, so it is called pressure antinode.
While an antinode is a point where the amplitude of oscillation is maximum i.e. displacement is maximum but pressure is minimum. So this point is called pressure node.
Hence displacement node coincides with pressure antinode and displacement antinode with pressure node.
(b) Bats emit ultrasonic waves of large frequencies (small wavelength) when they fly. These ultrasonic waves are received by them after reflection from the obstacle. Their ears are so sensitive and trained that they not only get the information ofthe distance of the obstacle but also that of the nature of the reflecting surface.
(c) The quality of the sound produced by an instrument depends upon the number of overtones. Since the number of overtones is different in the cases of sounds produced by violin and sitar therefore we can distinguish through them.
(d) Solids possess both the volume elasticity and the shear elasticity. Therefore they can support both longitudinal and transverse waves.
On the other hand, gases have only the volume elasticity and no shear elasticity, so only longitudinal waves can propagate in gases.
(e) A sound pulse is a combination of waves of different wavelengths. In a dispersive medium, the waves of different wavelengths travel with different speeds in different directions i.e. with different velocities. So the shape of the pulse gets distorted i.e. a plane wavefront in a non- dispersive medium does not remain a plane wavefront in a dispersive medium.