(needs medium) elastic, posses inertia, gives minimum
resistance Waves Electromagnetic (do not need medium) Mechanical
Ripple TransverseLongitudinal Safe Hands
Slide 4
Ripple TransverseLongitudinal Comp.& rare. Crest & Turf
P, changes stress changes Need shape elasticity Pass through S,L,G
Pass through S or L surface Need volume elasticity Safe Hands
Slide 5
Longitudinal Wave wave particles vibrate back and forth along
the path that the wave travels. Compressional Wave Safe Hands
Slide 6
Waves transfer energy without transferring matter. Frequency=
number of waves/time Safe Hands
Slide 7
Water Waves Safe Hands
Slide 8
Velocity of longitudinal waves is given by Newton as Newton
assumed propagation as isothermal process and then bulk modulus for
gas in isothermal condition is P thus speed is Sound waves Sound
energy is transferred by Longitudinal waves Sound waves can not be
polarized Safe Hands
Slide 9
When values are substituted the theoretical value is less
(280m/s) than the observed value(331m/s). Laplas corrected that
propagation of sound is not isothermal it is adiabatic thus E = P
then value matches with observed value. Thus v = ( P/ ) Safe
Hands
Slide 10
Medium velocity m/sec air (20 o C) 343 air (0 o C) 331 water
(25 o C) 1493 sea water 1533 diamond 12000 iron 5130 copper 3560
glass 5640 Safe Hands
Slide 11
Factors affecting the speed of sound Effect of pressure: There
is no effect of change in pressure on speed of sound Effect of
Temperature : Speed of sound is proportional to square root of
temperature.( if medium is same) Effect of molecular weight of
medium: Speed of sound is inversely proportional to square root of
molecular weight.( if temperature is same) Safe Hands
Slide 12
Factors affecting the speed of sound Effect of density: Speed
of sound is inversely proportional to square root of density of
medium Effect of humidity: When humidity increases the amount of
water vapors in air increases as water vapors are of less density
than of air the effective density of humid air decreases. Hence
velocity of sound increases in humid air. Velocity of sound is more
in summer days due increase in temperature. Velocity of sound is
more in rainy days due increase in humidity. Safe Hands
Slide 13
Transverse waves Crests: Highest part of a wave Troughs : The
low points of the wave Safe Hands
Slide 14
Reflection of wave T- waveL- wave From rigid surface From free
surface From rigid surface From free surface phase = phase = 0
phase = phase = 0 CTTCCTTC CCTTCCTT C R R C C C R R Safe Hands
Slide 15
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Slide 19
Ultrasound - sound waves with frequencies above the normal
human range of hearing. Sounds in the range from 20-100kHz
Infrasound - sounds with frequencies below the normal human range
of hearing. Sounds in the 20-200 Hz range Safe Hands
Slide 20
Analytical representation of sound waves In general progressive
waves are represented by F(v-xt) If y represents displacement of a
particle of medium at a distance x and at time t then we may have
an equation y = A sin ( t- ) = A sin ( t- (2 x/t)) Safe Hands
Slide 21
n Should I take n common or not Or Should it be just Just
substitute n= 1/T and dont forget n =V w Safe Hands
Slide 22
Principle of superposition of waves When two or more waves
traveling through a medium arrive at a point of the medium
simultaneously, each wave produces its own effect (displacement) at
that point independently of the others and the resultant effect
(displacement) at that point is equal to the vector sum of the
individual displacements of all the waves. Let Y 1, Y 2, Y3 Y3 - -
- - - be the individual displacements due to each wave. When all
the waves acting simultaneously then the resultant displacement y
is given by Y = Y1 Y1 + Y2 Y2 + + Y3 Y3 + - - - - - Safe Hands
Slide 23
Three cases of superposition of waves (i) Interference of waves
: Two waves of the same frequency traveling along the same path
with the same speed in the same direction. This gives rise to the
phenomenon of interference of waves. There are two types of
interferences:(a) Constructive interference (b) Destructive
interference Safe Hands
Slide 24
Interference the result of two or more sound waves overlapping
Safe Hands
Slide 25
Three cases of superposition of waves (ii) Stationary waves:
Two waves of the same amplitudes and same frequencies traveling
along the same path with the same speed in the opposite directions.
This gives to the phenomenon of stationary waves. Safe Hands
Slide 26
Three cases of superposition of waves (iii) Beats: Two waves of
slightly different frequencies traveling along the same path with
the same speed in the same direction. This gives rise to the
phenomenon of beats. Safe Hands
Slide 27
Theory of beats When two sound waves of same amplitude but
slightly different frequencies traveling along the same path with
the same speed in the same direction, the resultant amplitude thus
intensity is alternately maximum and minimum. This phenomenon is
called beats. The maximum intensity of sound is called waxing and
minimum intensity of sound is called waning. One waxing and one
waning constitute one beat. The time interval between two
successive waxing or waning is called the period of beats. The
number of beats per second is called the frequency of beats. The
frequency of beats is equal to the difference in the frequencies of
the two sound waves. Safe Hands
Slide 28
Analytical approach to beats If two sound waves sound waves
producing beats are given by equations Y 1 = Asin2 n 1 t & Y 2
= Asin2 n 2 t then their resultant can be obtained by using the
relation sinA + sinB = 2(cos(A-B)/2).(sin(A+B)/2) Y = {2A (cos (n 1
n 2 )t)}.sin2 ((n 1 + n 2 )/2)t. this sound is of frequency (n 1 +
n 2 )/2 such that its amplitude is varying between maxima and
minima with frequency ( n 1 n 2 ). Safe Hands
Slide 29
If this frequency means beat frequency is more than 20 Hz then
we can not distinguish between the maxima and minima thus a sound
of frequency (n 1 + n 2 )/2 will be heard, this is called as
difference tone. Safe Hands
Slide 30
Application of beats (1) The phenomenon of beats is used to
determine the frequency of turning fork. Remark (i) when the prongs
of a turning fork are loaded with wax, the frequency of fork
decreases. (ii) When the prongs of turning fork are filled, the
frequency of fork increases. (2) The phenomenon of beats is used to
tune musical instruments: (3) The phenomenon of beats is applied in
detection of harmful gases like methane in a mine (4) To produce
intermediate frequency Safe Hands
Slide 31
Dopplers effect The apparent change in the pitch (or frequency)
of sound due to the relative motion between source of sound and
observer (listener) is called Doppler effect. The frequencies are
related by upper signs indicate relative approach, lower signs
relative recession. Safe Hands
Slide 32
Slide 33
Applications of Doppler effect Dopplers effect is used in The
working of RADAR (RAdio Detection And Ranging) an equipment is used
to detect aero plane along with its speed. is used to determine the
speed of stars and planets. in the working of SONAR (SOund waves
Navigation And Ranging) the equipment is based on Doppler
effect.This equipment is used to detect submarines and its speed is
used to determine the speed of rotation of the Sun. Is used to
study motion of galaxies Function and state of heart valves Used by
bats, Scorpios to detect and catch the food Safe Hands
Slide 34
Musical Sound Sound produced by periodic vibrations is called a
musical sound. When sound is produced by non periodic vibrations it
is called as noise. Musical interval : The musical interval between
the two notes is defined as the ratio of the frequency of higher
note to the frequency of lower note. Some slandered ratios are as
follows. Unison: Here the musical interval = 1or N 2 =N 1 Octave:
Here the musical interval = 2 or N 2 = 2N 1 Hence N 2 is the octave
of N 1. Major tone: Here the musical interval =9/8 N 2 = 9N 1 /8
Minor tone: Here the musical interval = 10/9. N 2 = 10N 1 /9 Semi
tone: Here the musical interval = 16/15. N 2 = 16N 1 /15 Safe
Hands
Slide 35
Words used in musical sound (i) Loudness (L): It is the
sensation received by the ear due to intensity of sound. Loudness
depends upon the sensitivity of the listener ear. Therefore,
loudness of a sound of a given intensity may be different for
different listeners. Loudness (L) of sound increases with intensity
of sound according to Weber-Fechner law in physiology. According to
this law, L log I,L=K log I, where K is a constant. This relation
is known as Weber- Fecher relation. Loudness is measured in Bell
Safe Hands
Slide 36
(ii) Pitch: It is the characteristic of musical sound by which
a shrill (sharp) sound can be distinguished from a grave (or flat)
one, even though the two sounds may be of the same intensity. Pitch
means non quantitative frequency. (i) The buzzing of bee has high
pitch but low loudness while the roar of a lion has large loudness
but low pitch. (ii) Due to hormones usually the pitch of female
voice is higher than her male. Words used in musical sound Safe
Hands
Slide 37
Words used in musical sound Low pitch high intensity High pitch
low intensity Safe Hands
Slide 38
Words used in musical sound (iii) Quality (or Timbre): It is
the characteristics of musical sound, which enables us to
distinguish between two sounds of the same pitch and loudness. A
musical instrument vibrates with many frequencies at same time, the
lowest frequency is called as fundamental, and multiples are called
as overtones. The quality is determined by the number of overtones
and their relative intensities. Safe Hands
