Reflection of sound
Take
two metal tubes A and B. Keep one end of each tube on a metal plate as shown in
Fig.. Place a wrist watch at the open end of the tube A and interpose a
cardboard between A and B. Now at a particular inclination of the tube B with
the cardboard, ticking of the watch is clearly heard. The angle of reflection
made by the tube B with the cardboard is equal to the angle of incidence made
by the tube A with the cardboard.
Applications of reflection of sound
waves
(i)
Whispering
gallery : The famous whispering gallery at St. Paul?s
Cathedral is a circular shaped chamber whose walls repeatedly reflect sound
waves round the gallery, so that a person talking quietly at one end can be
heard distinctly at the other end. This is due to multiple reflections of sound
waves from the curved walls (Fig.).
(ii)
Stethoscope
:
Stethoscope is an instrument used by physicians to listen to the sounds
produced by various parts of the body. It consists of a long tube made of
rubber or metal. When sound pulses pass through one end of the tube, the pulses
get concentrated to the other end due to several reflections on the inner
surface of the tube. Using this doctors hear the patients? heart beat as
concentrated rays.
(iii)
Echo
: Echoes
are sound waves reflected from a reflecting surface at a distance from the
listener. Due to persistence of hearing, we keep hearing the sound for 1 /10th
of a second, even after the sounding source has stopped vibrating. Assuming the
velocity of sound as 340 ms?1, if the sound reaches the obstacle and returns
after 0.1 second, the total distance covered is 34 m. No echo is heard if the
reflecting obstacle is less than 17 m away from the source.
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