" WAVES "
Wave
A wave is a disturbance that moves through a medium. The energy is transferred from one point to another without transport of any matter.
Frequency
It is the no. of waves passing through a point in the medium in one second (unit is Hertz).
Wave Length
The distance between two consecutive crests or two consecutive troughs is called wave length .
For the light waves, if the wave length is different, color of the light will be different.
Amplitude
The maximum displacement of the particle of the medium is called the amplitude of the wave.
When something vibrates it produces a sound. The energy of the the vibrations is passed on to the molecules in the surrounding air and makes them move. Thus the sound wave falls on the ear and the sound is heard. The stronger the vibrations, the longer the amplitudes and the louder the sounds.
Velocity
Wave velocity is the distance through which the wave moves in one seconds. Velocity of light is more than the velocity of sound, so in a thunderstorm, lightning will always be seen before the clap of thunder.
Waves are of two types
Transverse wave
If the displacement of the individual atoms or Molecules is perpendicular to the direction of the wave, the wave is called a Transverse wave ( light wave ).
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| Transverse wave |
Longitudinal wave
If the displacement of the individual atoms or molecules is parallel to the direction of the wave, the wave is called a Longitudinal wave ( sound wave ).
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| Longitudinal wave | | | | | |
SOUND
STANDING WAVES
In a string fixed on both ends, when we strike or pluck at some point, waves propagate towards both ends & after reflection from the ends, overlap on each other to produce standing waves.
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SOUND STANDING WAVES |
A violin string oscillates at a fundamental frequency.
Musical Instruments.
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Musical Instruments.
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Wind instruments.
Standing wave can also be produced in air columns. In organ pipes(open at both ends), bugle & flute (closed at one end) and in tabla & dholak (closed at both ends) standing waves on air column produces sound.
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Wind Instruments. |
Different tones are produced by the same instrument depending on the type of vibrations. Here the fundamental & first two overtones are shown for both open end & closed at one end air column vibrations.
The wavelength (l) of the sound wave depends on the length (L) of the air column.
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| Wind instrument |
String instruments.
The simplest form of string instrument is just a stretched string over a resonating body to amplify the sound.The standing waves produced in strucked string (piano) bowed string(violin)& plucked string (sitar & sarod) musical instruments produce a range of musical sounds.
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| Musical Instruments |
AUDIBLE FREQUENCY RANGE
We can hear the sound if the frequency lies between 20 Hz. to 20 kHz. We hear low frequencies as low pitched and high frequencies as being high pitched.
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| AUDIBLE FREQUENCY RANGE |
ULTRASONIC & SUBSONIC WAVES
Sounds above audible frequency are called ultrasonic and sounds below audible frequency are called infrasonic or subsonic sounds.
Elephants use very low-pitched sounds, below the level of human hearing ( subsonic sounds), that call other members of the heard over many miles.
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ULTRASONIC & SUBSONIC WAVES |
APPLICATIONS OF ULTRASONIC SOUNDS
1. Sonar receptors in Bats &Whales:- The bats & whales send out some ultrasonic rays, which bounce back from the prey and are received by this system and they can locate the prey.
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| Sonar receptors in Bats &Whales |
2. Application in Medicine :- Instead of stethoscope ultra-sonography is used as a tool by physicians, to scan abdominal, pelvic and cardiac areas.
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| Application in Medicine |
Ocean Depth
3. Ocean depth can be found by measuring the time between sending out an ultrasonic signal and receiving the echo reflected from the ocean bed.
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| Ocean depth |
Detection of MINERAL OIL
4. Oil layer reflects a certain pattern of echoes which is detected by a seismograph.
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| Detection of MINERAL OIL |
Doppler effect
As the car moves away,wave fronts of its whistle take longer time to reach a listener, who hears a drop in pitch.- Long Wavelength -Low Frequency
As the car comes closer, sound wave fronts reach a listener ever more quickly and seem to rise in pitch. Small Wavelength- High Frequency.
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| Doppler effect |
Tuning Fork
When we strike a tuning fork, it will vibrate in a fixed frequency and a particular sound will be heard.
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| Tuning Fork |
Sound waves produced by a tuning fork.
Acoustics of Auditorium
The clearest speech is heard in an auditorium when there is a time gap of 1/20th of a second between the reflected rays and the direct rays, otherwise they will overlap and no sound can be heard clearly.
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| Acoustics of Auditorium |
TEST YOURSELF
