2. Just a simple example…
Our vocal chord is a source that
produces sound. this sound wave
carries power and energy.
Production of sound energy is due
to vibration of the chords in which
converts the mechanical energy
into sound energy.
The greater the waves amplitude
the more energy the wave carries.
This wave energy can change over
time known as power: P= E/t
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a
3. NOW… the question is where does this
sound power go to?! …well
EVERYWHERE..!!! it spreads out in all the
directions. IF we are at a certain distance
from a source of sound, for example
someone talking to us, we will hear the
same loudness sound independent of where
we are standing: either in front of the
person or behind him it wouldn’t matter.
loudness of a voice depends on how far we
are from that sound source.
** Loudness is a physical property associated
with intensity.
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4. . Intensity of any wave is the rate of power of that wave per area. Also for
area the only geometric shape that has all points equal distance away from a
source is a sphere (4pi.r^2).
I = ⟨P⟩/A
All points within this area get the same intensity( loudness).
. For sound power we have this formula:
P= (1/2) MV(w^2)(A^2)
and so
I = (1/2)(p)(v)(w^2)(A^2) **p as in mass density
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5. we are used to measure sound we hear in loudness.
For example the sound of your friend is loud when
she is yelling at you and on the other hand her
sound is not loud when she is whispering to you.
As we said before Intensity is the amount of
energy a sound has over an area; based on the
upper example
a) when we shout, the sound power produced is
higher and so it carries more energy with itself
and so the INTENSITY is higher.
b) when we whisper the sound power produced is
low and so it carries less energy with itself and so
the INTENSITY is lower.
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6. let’s combine our knowledge and solve this question
Q: Determine the amplitude of sound wave if the wave travels
at a frequency of 1000 Hz in air of density 2 kg.m^-3 at 400
ms^-1 with an intensity of 10 Wm^-2 ??
