1. SOUND WAVES, REFLECTION & REFRACTION
Lecture No. 17
By. Sajid Hussain Qazi

2. 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.

3. Sound Waves Each Sound wave has unique pattern, Frequency Wavelength
Amplitude

4. 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

5. 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

6. 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
Reverberations-
Multiple reflections of sound within a room
The walls of concert halls are designed to make the reflection of sound diffuse

7. 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

8. Refraction of Sound

9. Speed of Sound Medium Velocity m/sec Air (20 C) 343 Air (0 C) 331
Water (25 C)
Sea water
Diamond
Iron
Copper
Glass

10. 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.

11. 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

12. 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.

13. 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.

14. 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).