CLASS 〖푿푰〗^풕풉 MAHARASHTRA STATE BOARD PHYSICS Chapter 6 - SOUND

1. How do you come to know that a class is over
in your school/college?

2.  How do you come to know that a class is
over in your school/college?
Because you
hear the ringing
of a school /
college bell.

3. How you come to know that someone is at your door?

4. When
he/she
knocks or
you hear the
ring of the
door bell

5. Chapter 6 - SOUND
CLASS 𝑿𝑰 𝒕𝒉
MAHARASHTRA STATE BOARD
PHYSICS
By – Miss. Pooja K More

6. Try this
Put your finger on your
neck and say “aaahh” as
loud as you can
What you feel?

7. You cannot only hear the sound but you can
feel the vibration inside your throat.
• It is the form of energy
• It comes from a vibrating source.
• Sound travels in invisible waves.
• Sound can travel through solids, liquids, and gases.

17. Sound
In physics, sound is a
vibration that typically
propagates as an audible
wave of pressure, through a
transmission medium such
as a gas, liquid or solid.

18. Wave
A wave is a kind of
oscillation (disturbance) that
travels through space and
matter. Wave motions
transfer energy from one
place to another.

19. 1- The voice box is called:
a. Stomach
b. Heart
c. Larynx
d. Mouth
2- To an fro motion of an object is called
a. Waves
b. Amplitude
c. Vibration
d. All of the above
3- What kind of musical instrument is a sitar?
a. String
b. Membrane
c. Wind
d. None

20. Types of waves
Different types of waves
have a different set of
characteristics. Based on
the orientation of
particle motion and
direction of energy,
there are three
categories-

21. Mechanical wave
• Those waves which cannot
transmit their energy through
a vacuum and require a
medium for same are called
mechanical waves
• Mechanical waves, such as
water waves or sound waves,
travel within, or on the surface
of, a material with elastic
properties

22. Electromagnetic wave
• Electromagnetic waves are formed when an
electric field comes in contact with a magnetic
field. They are hence known as ‘electromagnetic’
waves.
• Examples of EM waves are radio waves,
microwaves, infrared waves, X-rays, gamma rays,
etc
• In other words, EM waves are composed of
oscillating magnetic and electric fields.
• They are also perpendicular to the direction of
the EM wave.
• EM waves travel with a constant velocity of 3 x
108 m/s in vacuum.
.

23. Matter wave
• Matter is made of atoms,
and atoms are made
protons, neutrons and
electrons.
• These are not macroscopic
particles.
• Matter waves discovered in
elementary particles, can
display wave like behaviour

24. Common properties of all waves
 Amplitude (A)
 Wavelength (𝛌)
 Period (T)
 Double periodicity
 Frequency (n)
 Velocity (v)
 Medium for propagation of mechanical wave
 Phase
 Phase difference https://youtu.be/a8d63RuWlsk?t=118

25. AMPLITUDE (A)
• Amplitude, in physics, the
maximum displacement or
distance moved by a point
on a vibrating body or wave
measured from
its equilibrium position.
• It is equal to one-half the
length of the vibration path.

26. WAVELENGTH (𝛌)
• Wavelength can be defined
as the distance between
two successive crests or
troughs of a wave.
• It is measured in the
direction of the wave.
• Wavelength is inversely
proportional to frequency.

27. PERIOD (T)
• The time taken for one
complete oscillation in
the density of the
medium is called the
time period of the
sound wave.
• It is represented by the
letter T

28. Double periodicity
• The wave motion
has double periodicity. i.e.
It is periodic in space
& periodic in time.
• Wave can be defined as an
oscillatory disturbance
traveling through a
medium without change
of form.

29. FREQUENCY (n)
- The number of waves
produced in a given time.
- SI unit of frequency is hertz
(Hz)
Frequency is a reciprocal of time period, i.e.,
n =
𝟏
𝑻

30. Velocity (v)
• The distance covered by a wave
per unit time is called the velocity
of wave.
• During the period (T) , the wave
covers a distance equal to the
wavelength (𝛌).
• Therefore the magnitude of
velocity of wave is given by,
Magnitude of velocity =
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝛌)
𝑇𝑖𝑚𝑒 (𝑇)

31. Properties of medium for propagation
of mechanical wave
• The medium should be continuous and elastic so that the medium
regains original state after removal of deforming forces.
• The medium should possess inertia. The medium must be capable
of storing energy and of transferring it in the form of waves.
• The frictional resistance of the medium must be negligible so that
the oscillations will not be damped.

32. Phase
• The state of oscillation of a
particle is called its phase.

33. Phase difference
• Phase Difference is used to describe
the difference in degrees or radians
when two or more alternating
quantities reach their maximum or
zero values
• If we measure the distance travelled
by two waves and then compare
those distances, any difference in the
distances travelled is called the path
difference. Path difference is
measured in metres (m)

34. QUIZ
• What is the speed of sound in air?
A. 330 m/s
B. 332 m/s
C. 334 m/s
D. 336 m/s
Ans. B
• In which of the following the sound cannot travel?
A. Solids
B. Liquids
C. Gases
D. Vacuum
Ans. D

35. Graph
• Using axes of
displacement and
distance, sketch two
waves A and B such that
A has the twice the
wavelength and half the
amplitude of B

36. PROGRESSIVE WAVE
• A progressive wave is a term
given to a wave that travels
from a specific point A in the
medium to another point B.
• In simple terms, a wave that
continuously travels in a
medium in the same direction
minus the changes is known as
a travelling wave or progressive
wave.

37. CHARACTERISTICS OF PROGRESSIVE WAVE
• All vibrating particles of the medium have
same amplitude, period and frequency.
• State of oscillation i.e., phase changes from
particle to particle.

38. TYPES OF PROGRESSIVE WAVE
• Waves move energy from one
place to another.
• There are two types of waves,
transverse and longitudinal.

39. LONGITUDINAL WAVE
• A wave vibrating in the
direction of propagation.

40. Longitudinal wave cannot be polarised
• Longitudinal waves can't be polarised because their
particles vibrate in the same direction that the wave travels.
• Sound waves are longitudinal waves .
• They cause particles to vibrate parallel to the direction of wave
travel.
• When travelling through air, the speed of sound is about 330
metres per second (m/s).
• Sound cannot travel through a vacuum because there are no
particles to carry the vibrations.
https://youtu.be/K0vaLj2ZRA4?t=90

41. Compression and Rarefaction
• A compression is a region
in a longitudinal wave
where the particles are
closest together.
• A rarefaction is a region in
a longitudinal wave where
the particles are furthest
apart.

42. Characteristics of longitudinal wave

43. Transverse wave
• A wave in which the
medium vibrates at right
angles to the direction of
its propagation.
• A simple example is given by
the waves that can be created
on a horizontal length of
string by anchoring one end
and moving the other end up
and down.

44. Crest and Trough
• Waves have
moving crests (or peaks)
and troughs.
• A crest is the highest point the
medium rises to and a trough is
the lowest point the medium
sinks to.
• A crest is a point on
the wave where the
displacement of the medium
is at a maximum.

45. Transverse wave can be polarised
• When transverse waves have their
particles always vibrating in the same
plane, the wave is said to be
"plane polarised".
• Longitudinal waves can't
be polarised because their particles
vibrate in the same direction that
the wave travels.

47. Difference Between Transverse and Longitudinal wave

48. WHAT TYPE OF WAVE IS A SOUND WAVE
• Sound is a form of energy which makes us hear.
• The sensation felt by our ears is called sound.
• We hear several sounds around us in our everyday life.
• We know that sound travels in the form of wave.
• A wave is a vibratory disturbance in a medium which carries energy from one
point to another without there being a direct contact between the two points.
• A wave in which the particles of the medium vibrate back and forth in the
‘same direction’ in which the wave is moving.
• Medium can be solid, liquid or gases.
• Therefore, sound waves are longitudinal waves.
• Sound is a longitudinal wave which consists of compressions and rarefactions travelling
through a medium.

49. • The vibrations from sound waves cause our ears to send signals to our brains to
create sound.
• Sound waves are important because they allow us to hear important messages
and emergency signals to protect ourselves.
• Sound surrounds you, traveling in waves throughout the atmosphere.
• These waves occur as a result of atoms vibrating and colliding with one another.
• These vibrations occur from a source and travel throughout the atmosphere - the
vibrations creating waves of energy.
• Humans and other creatures use these sound waves, not only to communicate
but also to perform various tasks.
• Communication
• Ocean Exploration
• Underground Resources
• Hunting
Sound wave are important

50. Different types of sound

51. Decibel(dB) level
 Decibel (dB) level of
everyday sound
Sound's loudness is
measured
in decibels (dB).
Normal conversation
is about 60 dB, and
a loud rock concert
is about 120 dB.

52. 1)When the sound intensity is above 120 Decibel, what happen to
human ears?
Answer: Very painful to withstand.
2) What is ultrasonic sound?
Answer: It is sound of frequency more than 20KHz (20,000 cycles / sec).
3) What is frequency?
Answer: The number of vibrations made by a body in one second is called
its frequency.
4) What is audio frequency?
Answer: Audio frequency is the frequency of audio sounds.
5) What is the formula of velocity?
Answer: Velocity is equal to frequency * wavelength.
6) Give an example of transverse wave?
Answer: Light wave.

53. Numerical
• A sound wave travels with a speed of 330m/s^-1 in the
air. If the wavelength of the wave is 3.3m, what is the
frequency?
Solution: Velocity of wave = wavelength / time taken
Frequency = 1/ time taken
Therefore,
Velocity = wavelength*frequency
330/3.3 = frequency
Therefore,
Frequency = 100 hertz

56. • When the speed of any object
surpasses the speed of sound
waves, the speed of respective
object is known as supersonic
speed.
Sonic Boom
• The shock waves produce a very
sharp and loud sound, which is
known as sonic boom.
• For example, the speed of
bullets, jet aircrafts, etc.

57. Hearing Aid
• The hearing aid is an
electronic device the help
deaf people to listen
properly.
• A hearing aid is a
battery operated device
that receives sound
through a microphone.

58. Principle of superposition of waves
• The superposition
principle states that
when two or
more waves overlap in
space, the resultant
disturbance is equal to
the algebraic sum of the
individual disturbances.

59. Echo
• Repetition of the original sound
• Some rigid surface at a distance
from the source of sound
• Distance = speed χ time
• If you shout or clap in
a especially mountains
region, after a while, you will
hear the same sound, it is
known as echo.

60. Why can’t we hear an echo at every place?
• They can't hear an echo in
small room because in it the
sound can't be reflected
back.
• For an echo of a sound
to be heard, the minimum
distance between the source
of sound and the walls of the
room should be 17.2 m.

61. • An observer stands at a distance of 850m from a
cliff and fires a gun. After what time gap will he
hear the echo, if sound travels at a speed at
350 m/s in air?
Answer: We know,
d= v x t x 2
t= 2 × d x v
=2 × 850 x 350
=20s

62. Reverberation
• The repeated reflection
that results in the
persistence of sound
waves is known
as reverberation.
• E.g. in a big hall
especially, an
auditorium, the
excessive reverberation
can be heard.

63. Acoustics
• Acoustic waves are mechanical and
longitudinal waves (same direction of vibration
as the direction of propagation) that result from
an oscillation of pressure that travels through a
solid, liquid or gas in a wave pattern.
• These waves show numerous characteristics
including wavelength, frequency, period and
amplitude.

65. Medical applications of acoustics
• Shock waves which are high pressure high amplitude
waves are used to split kidney stones into smaller pieces
without invasive surgery.
• Reflection of ultrasonic waves from regions in the of
the interior of body is used for ultrasonic imaging.
• It is used for prenatal (before the birth) examination,
detection of anomalous conditions like tumour etc and
study of heart valve action.

66. Other applications of acoustics
• SONAR is an acronym for Sound
Navigation Ranging. This is a
technique for locating objects
underwater. This system is useful to
measure motion and position of the
submerged objects like submarine.
• Acoustic principle has important
application to environmental
problems like noise control.

67.  So, basically sound helps us to communicate with the other
person.
 For example, we can hear the musical instruments like tabla,
flute, a guitar due to vibration.
 The characteristics of sound are as follows:
• Pitch
• Loudness
• Quality
Characteristics of Sound

68. Pitch
• We can identify a female and male
voice without seeing them.
• The term ‘pitch’ is often used in
music.
• Pitch depends upon the frequencies
of the sound wave.
• A note has a higher pitch when the
frequency is high and a note of low
frequency has a low pitch.
• The sound with a high frequency is
called as shrill.

69. Loudness
• The loudness is a sensation of how strong a sound wave is at a
place.
• It is always a relative term and is a dimensionless quantity.
• Loudness is measured in decibel (dB).
• It is given as:
L = log(I), here ‘I’ is the intensity.
• The loudness depends on the amplitude of the vibration.
• It will be louder when the amplitude is high.
• Intensity is more, loudness is more
• I ∝ 𝐴2

70. Timbre or quality
• The word timbre also describes the term
quality.
• As different sources produce different sounds,
the timbre helps us to distinguish between
them.
• A sound of good quality is pleasant to listen.
• The instruments are of different shapes and
size and they produce different harmonics of
loudness hence their sound can be easily

71. • Another term for a sound reflection off of a wall or other object
through which a sound wave cannot pass is
a) Amplitude
b) Echo
c) Reverberation
d) Vibration
Answer: b) Echo
• Before the main shock waves, the earthquake produces the
characteristic sound waves which some animals like rhinoceros can
hear. Can you guess the kind of sound waves produced here?
a) Infrasonic sounds
b) Ultrasonic sounds
c) Audible Sounds
d) All of these
Answer: a) Infrasonic sounds

72. Thank you