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# TNPSC Free Notes Physics In English – Sound

இந்தக் கட்டுரையில், TNPSC குரூப் 1, குரூப் 2, குரூப் 2A, குரூப் 4 மாநிலப் போட்டித் தேர்வுகளான TNUSRB, TRB, TET, TNEB போன்றவற்றுக்கான  முறைகள் இலவசக் குறிப்புகளைப் பெறுவீர்கள்.தேர்வுக்கு தயாராவோர் இங்குள்ள பாடக்குறிப்புகளை படித்து பயன்பெற வாழ்த்துகிறோம்.

### Sound

Sound is a form of energy which produces sensation of hearing in our ears.

Longitudinal Waves:
 Sound waves are longitudinal waves

 High and low pressure regions called compressions and rarefactions.

Characteristics of sound waves:
Amplitude (A):
The maximum displacement of the particles of the medium from their original undisturbed
positions, when a wave passes through the medium is called amplitude of the wave. Amplitude is
denoted as A. Its SI unit is meter (m).
Frequency (n):
The number of vibrations (complete waves or cycles) produced in one second is called frequency
of the wave. It is denoted as n. The SI unit of frequency is s –1 (or) hertz (Hz).
Time period (T):
The time required to produce one complete vibration (wave or cycle) is called time period of the
wave. It is denoted as T. The SI unit of time period is second (s)
Wavelength (λ):
The minimum distance in which a sound wave repeats itself is called its wavelength. The
wavelength is usually denoted as λ (Greek letter, lambda). The SI unit of wavelength is metre
(m).
Velocity or speed (v):
The distance travelled by the sound wave in one second is called velocity of the sound. The SI
unit of velocity of sound is m s –1 .
Categories of sound waves based on their frequencies:
 Audible waves – 20 Hz and 20,000 Hz.
 Infrasonic waves – below 20 Hz

 Ultrasonic waves – greater than 20 kHz
Distinguishing different sounds:
 Loudness and intensity
 Pitch
 Timbre
Loudness and Intensity:
 Differentiate the sounds of different frequencies
 The unit of intensity of sound is decibel (db).
Pitch:
 Distinguish weather a sound is shrill or base.
 High pitch sound is shrill and low pitch sound is flat.
Timbre:
Timbre is the characteristic which distinguishes two sounds of same loudness and pitch emitted
by two different instruments.
Speed of Sound:
 Speed (v) = One wavelength (λ)/One time period (T)
 v = λ/T
 T = 1/n
 v = n λ.
 In any medium the speed of sound increases if we increase the temperature of the
medium.
Reflection of Sound:
 The angle in which the sound is incident ∠I is equal to the angle in which it is reflected
∠r .
 Direction of incident sound, the reflected sound and the normal are in the same plane.

Application of reflection sound:
 Sound board
 Ear trumpet
 Mega phone
Echo:
 340 ms –1 at 25°c
 Minimum distance -17m
 The sensation of sound persists in our brain for about 0.1s

Applications of echo:
 Communication of animals and to find their prey.
 Obstetric ultrasonography.

 To determine the velocity of sound waves in any medium.

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