Page 22 - Physics 10_Float

SOUND

This compressed air layer in turn compresses the layer
next to it and so on. A moment later, the prong begins to Physics Insight
move from B towards A (Fig.11.6-c). Now the pressure in
the adjacent layer decreases and a rarefaction is
produced. This rarefaction is transfered to the air layer
next to it and so on. As the tuning fork moves back and
forth rapidly, a series of compressions and rarefactions
are created in the air. In this way, sound wave propagates Illustration of longitudinal
through the air. wave formed by vibrating
tuning fork in the air.
As in the Fig.11.6, the direction of propagation of sound wave Compressions are places
where air pressure is slightly
is along the direction of oscillating air molecules. This shows
higher than the surrounding
the longitudinal nature of sound waves. Distance between air pressure due to high
two consecutive compressions or rarefactions is the density of air particles. While
wavelength of sound wave. rarefactions are the regions
correspond to low air pressure
due to low density of air
11.2 CHARACTERISTICS OF SOUND particles.

Sounds of different objects can be distinguished on the basis Quick Quiz
of different characteristics as described below: Identify which part of these
musical instruments vibrates
Loudness: Loudness is the characteristic of sound by which to produce sound:
loud and faint sounds can be distinguished. (a) electric bell (b) loud
speaker (c) piano (d) violin
(e) flute.
When we talk to our friends, our voice is low, but when we Self Assessment
address a public gathering our voice is loud. Loudness of a 1. Explain how sound is
sound depends upon a number of factors. Some of them are produced by a school bell.
2. Why are sound waves called
discussed below:
mechanical waves?
3.Suppose you and your friend
(a) Amplitude of the vibrating body: The loudness of the are on the Moon. Will you be
sound varies directly with the amplitude of the able to hear any sound
vibrating body (Fig.11.7). The sound produced by a produced by your friend?
sitar will be loud if we pluck its wires more violently. Loud
Similarly, when we beat a drum forcefully, the Large
amplitude of its membrane increases and we hear a amplitude
loud sound.
Small
Quiet amplitude
(b) Area of the vibrating body: The loudness of sound Fig. 11.7: Variation of loudness
also depends upon the area of the vibrating body. with amplitude

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