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LESSON NOTES

Reflection of sound
When sound waves strike a surface, they return back into the same medium. This
phenomenon is called reflection.

Laws of reflection
There are two basic laws of reflection of sound:

(i) Angle of incidence is equal the angle of reflection. i = r

(ii) The incident wave, the reflected wave and the normal all lie in the same plane.

Applications of Reflection of Sound

Many instruments work on the basis of multiple reflections of sound:

1. Megaphone or speaking tube

Have you ever noticed that we need to cup our hands while calling a person’s name
standing far from us. It is because the hands prevent the sound energy from
spreading in all directions and the person can hear the call easily.
In the same way, people use horn-shaped metal tubes, commonly called
megaphones while addressing a group of people. In all such devices, the sound
energy is prevented from spreading out by successive reflections from the horn-
shaped tubes. Megaphone, loudspeakers, bulb horns, musical instruments like
trumpets, shehnais etc. are designed to send sound by multiple reflections in a
particular direction due to which the amplitude of sound waves adds up to increase
loudness of sound.