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 Reverberations- Multiple 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 Velocity m/sec Air (20 C) 343 Air (0 C) 331 Water (25 C) 1493 Sea water 1533 Diamond 12000 Iron 5130 Copper 3560 Glass 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).