Transcript SOUND WAVES, REFLECTION & REFRACTION

SOUND WAVES,
REFLECTION &
REFRACTION
Lecture No. 17
By. Sajid Hussain Qazi
Sound





Sounds are created by Moving molecule in
the medium ( Solid, Liquid and Gases),
Sounds are measured by Frequency,
Wavelength, Speed, and Amplitude,
Sounds can combine by interference,
Sounds can be changed by the Acoustics of
the Area or the speed of the source
(Doppler Effect),
Sounds are used in many devices.
Sound Waves
•
Each Sound wave has unique pattern,
•
Frequency
•
Wavelength
•
Amplitude
Sound Mediums


A medium is a material through which
sound, a form of energy, need to transfer
Speed of sound
 Solid
: Fast speed
 Liquid : Medium speed
 Gas
: Slow Speed

Standard Temperature and Pressure = 3.31 x 102 m/s
 Vacuum
: No Sound
Frequency of Sound




Pitch of the sound
Bass : Low frequency 0 to 300 Hz
Mid range : “voice” 300 to 6,000 Hz
Treble : High frequency, Above
“middle range” note, 6,000 to 20,000
Hz
Reflection of Sound





An echo is reflected
sound
Sound reflects from all
surfaces of a room
Acoustics is the study
of the way sound
reflects off of objects in
a room
ReverberationsMultiple reflections of
sound within a room
The walls of concert
halls are designed to
make the reflection of
sound diffuse
Refraction of Sound




Sound waves are refracted when parts of a
wave front travel at different speeds
This happens in uneven winds or
temperatures
Sound waves tend to bend away from
warm ground, since it travels faster in
warmer air
On a cold night, the speed of sound is
slower near the ground than above, so we
can hear over larger distances
Refraction of Sound
Speed of Sound
Medium
Air (20 C)
Air (0 C)
Water (25 C)
Sea water
Diamond
Iron
Copper
Glass
Velocity m/sec
343
331
1493
1533
12000
5130
3560
5640
Resonance of Sound



A driving force in tune with the natural frequency
(sometimes known as the resonant frequency) of an
oscillator can buildup larger amplitudes than the
oscillator could alone.
This buildup is known as resonance or sympathetic
vibration.
Imagine swinging on a swing. If someone pushes you
at the right time, the amplitude of your swing
increases. The pushing has to be at the correct
frequency, however.
Resonance of Sound





If someone pushes you at random intervals, the
chances will not cause you to swing very much
higher, but if the pushing is in tune with your
natural frequency, you can go very high indeed.
Put two tuning forks of equal frequencies side by
side, but not touching.
Strike one tuning fork so that you can hear its
tone, and then suddenly silence it. You can still
hear a faint tone.
This is because the second tuning fork has started
vibrating sympathetically.
So the resonance is frequency of sound waves
exactly matches the natural frequency of an object
Interference of Sound

The result of two or more sound or waves
overlapping.
 There
are two types of Interference,
 Constructive
Interference,
 Destructive Interference

CONSTRUCTIVE INTERFERENCE
-The displacement of the disturbance of TWO
waves are the same (Similar sounds)
-Frequency are the same or multiple.
Interference of Sound

DESTRUCTIVE INTERFERENCE
-The displacement of the disturbance of TWO
waves are the different (Unlike sounds)
-Frequency are the different or not a direct
multiple.
Doppler Effect

The frequency of the wave is changed
by the motion of the source,
 Frequency
will be increased when
the source approaches the sensor
(listener),
 Frequency will be decreased when
the source increases the distance
from the sensor (listener).