2. What is sound?
Sound is a form of energy which produces a
sensation of hearing in our ears.
Sound is produced due to vibration of different
objects.
3. Sound as a Wave
Sound travels as a longitudinal wave through a material
medium.
The medium can be solid, liquid or gas.
Sound travels as successive compressions and rarefactions in
the medium
4. Propagation of Sound
When a vibrating object moves forward, it
pushes and compresses the air in front of it
creating a region of high pressure. This
region is called a compression.
When the vibrating object moves backwards,
it creates a region of low pressure called
rarefaction (R).
6. Propagation of Sound
As the object moves back and forth rapidly, a series of compressions and
rarefactions is created in the air. These make the sound wave that
propagates through the medium.
7. Propagation of Sound
The propagation of sound can be visualized as propagation of
density variations or pressure variations in the medium.
8. Sound-a mechanical wave
Sound cannot travel in vacuum.
Sound is a mechanical wave and needs a material medium like air,
water, steel etc. for its propagation. It cannot travel through vacuum.
Sound waves are characterised by the motion of particles in the
medium and are called mechanical waves.
9. CHARACTERISTICS OF A SOUND WAVE
The change in density from one maximum value
to the minimum value and again to the
maximum value makes one complete oscillation.
The distance between two consecutive
compressions or two consecutive rarefactions is
called the wavelength,represented by λ, (Greek
letter lambda)
The SI unit is meter(m).
10. CHARACTERISTICS OF A SOUND WAVE
The magnitude of disturbance in a medium on either side of the
mean value is called an amplitude (A).
As shown in the figure below, amplitude is the distance between
mean position and crest (maximum displacement).
11. CHARACTERISTICS OF A SOUND WAVE
The time taken by the wave for one complete
oscillation of the density or pressure of the medium
is called the time period, T.
SI unit is second (s).
The number of complete oscillations per unit time
is called the frequency (ν), Greek letter, nu.
SI unit is hertz(Hz), or 1/s
Frequency and time period are related as follows,
frequency=1/timeperiod or ν=1/T
12. Speed of sound
The speed of sound is defined as the distance
which a point on a wave travels per unit time.
λ is the wavelength, which is the distance
travelled in one time period.
Hence Speed= distance/time or v= λ/T
The speed v, frequency ν , and wavelength λ,
of sound are related by the equation,
v = λ /T or v=λν.
13.
14. Reflection of sound
Like light, sound gets reflected at the surface of a
solid or liquid and follows the laws of reflection.
i) The angle of incidence is equal to the angle of
reflection.
ii) The incident ray, the reflected ray and normal at
the point of incidence all lie in the same plane.
15. Echo
For hearing a distinct sound, the time interval
between the original sound and the reflected
one must be at least 0.1 s.
The minimum distance of the obstacle from
the source of sound must be 17.2 m.
16. USES OF MULTIPLE REFLECTION
OF SOUND
The curved ceilings of concert halls and conference
halls make the sound after reflection reach all
corners of the hall.
Sometimes a curved soundboard may be placed
behind the stage so that the sound, after reflecting
from the sound board, spreads evenly across the
width of the hall.
17. Properties of sound
Sound properties such as pitch, loudness and
quality are determined by the corresponding wave
properties.
The loudness or softness of a sound is determined
basically by its amplitude. The amplitude of the
sound wave depends upon the force with which an
object is made to vibrate.
18. Loudness and intensity
Loudness is a physiological response of the ear to the
intensity of sound.
The amount of sound energy passing each second through
unit area is called the intensity of sound.
19. Pitch
If the frequency of vibration is higher, the sound is shrill and has a
high pitch.
If the sound is said to have a lower pitch then it has a lower frequency
of vibration.
A bird produces high pitched sound whereas roaring of a lion is a low
pitched sound.
20. Ultrasound & infrasound
The waves having frequency
less than 20 Hz are infrasonic
waves.
A vibrating simple pendulum
produces infrasonic sounds.
Elephants and whales
produces infrasonic waves.
Earthquakes produces
infrasonic waves.
The waves having frequency
more than 20,000 Hz are
ultrasonic waves.
Bats and rats can produce
ultrasonic sounds.
21. Range of Hearing
The audible range of hearing for average human beings is in
the frequency range of 20Hz – 20 kHz.
Infrasound-sound with frequency lower than 20Hz.
Ultrasound-sound with frequency higher than 20KHz.
