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Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC

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                                                                               Waves & Sound

Wave motion

  • A wave is the disturbance produced in a physical medium which moves forward in the medium with a definite speed without change in its force.
  • Waves are of two kinds longitudinal waves and transverse waves.

Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC
Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC

 

Sound waves

  • sound travels in the form of waves.
  • Sound waves are longitudinal waves.
  • Thus, they do not exhibit polarisation.

Sound, a longitudinal wave

  •  Longitudinal waves are waves in which the motion of the individual particles of the medium is in a direction that is parallel to the direction of energy transport.
  • Sound waves in air (and any fluid medium) are longitudinal waves because particles of the medium through which the sound is transported vibrate parallel to the direction that the sound wave moves.

 

Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC
Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC
Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC

Longitudinal waves

Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC

 

Sound as a pressure wave

Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC

Wavelength

 

  • The wavelength of a wave is merely the distance that a disturbance travels along the medium in one complete wave cycle.

Frequency

  • The frequency of a wave refers to how often the particles of the medium vibrate when a wave passes through the medium. The frequency of a wave is measured as the number of complete back-and-forth vibrations of a particle of the medium per unit of time.
  • 1 Hertz = 1 vibration/second

Pitch

  • The sensation of a frequency is commonly referred to as the pitch of a sound.
  • A high pitch sound corresponds to a high frequency sound wave and a low pitch sound corresponds to a low frequency sound wave

Factors Affecting Wave Speed

  • The speed of any wave depends upon the properties of the medium through which the wave is travelling.
  • vsolids > vliquids > vgases

Doppler effect

The Doppler effect can be described as the effect produced by a moving source of waves in which there is an apparent upward shift in frequency for the observer and the source are approaching and an apparent downward shift in frequency when the observer and the source is receding. The Doppler effect can be observed to occur with all types of waves - most notably water waves, sound waves, and light waves.

Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC

Applications

Radar

  • Radio Detection And Ranging
  • Radar is an object detection system which uses radio waves to determine the range, altitude, direction, or speed of objects.
  • It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain.
  • The radar dish or antenna transmits pulses of radio waves or microwaves which bounce off any object in their path.
  • The object returns a tiny part of the wave's energy to a dish or antenna which is usually located at the same site as the transmitter.

Pulse Radar

Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC

  • SONSonar (acronym for SOund Navigation And Ranging ) is a technique that uses sound propagation to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. 

Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC

Sound board used in a big hall

Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC

Stethoscope

Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC

 

Curved ceiling of a conference hall

Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC

Range of Hearing

  • The audible range of sound for human beings extends from about 20 Hz to 20000 Hz (one Hz = one cycle/s)
  • Sounds of frequencies below 20 Hz are called infrasonic sound or infrasound.
  • Frequencies higher than 20 kHz are called ultrasonic sound or ultrasound.

Facts at a glance

Intensity of sound

KIND of AREA

Intensity during (decibel)

Intensity at night (decibel)

Industrial area

Commercial area

Residential area

Peaceful area

75

65

55

50

70

55

45

40

Applications of Ultrasound

  • Ultrasound is generally used to clean parts located in hard-to-reach places, for example, spiral tube, odd shaped parts, electronic components etc.
  • Ultrasounds can be used to detect cracks and flaws in metal blocks.
  • Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called ‘echocardiography’.
  • Ultrasound scanner is an instrument which uses ultrasonic waves for getting images of internal organs of the human body.
  • Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called ‘echocardiography’.
  • Ultrasound scanner is an instrument which uses ultrasonic waves for getting images of internal organs of the human body.
  • Ultrasound may be employed to break small ‘stones’ formed in the kidneys into fine grains.

Waves And Sound - Physics Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC

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