Echo:
The sound waves received after being reflected from a high tower or mountains
is called echo.
To hear echo, the minimum distance between the
observer and reflector should be 17m (16.6m).
Persistence of ear (effect of sound on ear)
is 1/10 sec.
Due to refraction, sound is heard at longer
distances in nights than in day.
Resonance:
if the frequency of imposed periodic force is equal to the natural frequency of
a body, the body oscillates with very large amplitude. This phenomenon is
called resonance.
Interference
of sound: The modification or redistribution of energy at a point due to
superposition of two (or, more) sound waves of same frequency is called
interference of sound.
If two waves meet at a point in same phase,
intercity of sound is maximum at that point. Such type of interference is
called constructive interference. Similarly, if the two waves meet at a point
in opposite phase, intensity of sound at that point is minimum. Such type of
interference is called destructive interference.
Diffraction
of sound: Wavelength of sound is of the order of 1 m. If an obstacle of
that range appears in the path of sound, sound deviates at the edge of obstacle
and propagates forward. This phenomenon is called diffraction of sound.
Doppler’s
Effect:
