Ch 12 Sound 2.pptbhcycygucuhbmmmmmntydtscudbddibudbd7dbdudbudbdudvdydvs6evs7vs7sjrr8eu4vuebfirj

Very enthusiastic

1. Sound Sound

2. What is sound?What is sound?
Sound is
◦A form of energy made by vibrations.
◦When an object vibrates it causes the air
particles around it to move.
◦These particles bump into particles close to
them and this continues until they run out of
energy.

3. Try this:Try this:
Put your finger on your neck and say
“aah” as loud as you can.
Now say it as soft as you can.
You can not only hear the sound, but you
can feel the vibration inside your throat.

4. How does sound travel?How does sound travel?
Sound travels through all forms of matter
— gases, liquids and solid.
These are called the medium.
Sound cannot travel through a vacuum.

5. What is pitch?What is pitch?
Pitch is how high or how low a sound is.
This is a high pitched sound.
This is a low pitched sound.
Pitch is how high or how low a sound is.
This is a high pitched sound.
This is a low pitched sound.

6. How does sound travel?How does sound travel?
Sound passes through the medium as
longitudinal waves.
When the vibrations are fast you hear a
high pitch. When they’re slow, you hear
a low pitch.
High Pitch Low Pitch

7. Louder
SofterHow else can we change sound? How else can we change sound?
We can make it louder or softer by
changing the amplitude of the height of
the wave.
The higher the amplitude, the louder the
sound. The lower the amplitude the
softer the sound.

8. How do musical instruments create How do musical instruments create
sound?sound?
It depends on the type of instrument.
There are four types.
◦Woodwind
◦String
◦Percussion
◦Brass

9. WoodwindsWoodwinds InstrumentsInstruments
Woodwinds make music by blowing on the
top of the instrument or on a reed.
Flute
Oboe
Clarinet
Bassoon
Piccolo

10. String InstrumentsString Instruments
Strings make music by plucking or
strumming the strings.
Violin
Cello
Electric
Guitar
Guitar Harp

11. Percussion InstrumentsPercussion Instruments
Percussion instruments make music by
striking, shaking or scraping them.
Drum
Cymbals
Tambourine
Xylophone
Piano
Maracas

12. Brass InstrumentsBrass Instruments
Brass instruments make music by buzzing
lips while blowing.
French Horn
Trumpet
Trombone
Tuba

13. Sound needs a medium to Sound needs a medium to
travel travel :-:-
Sound is a mechanical wave and needs a medium for propagation.
Sound travels through solids, liquids and gases. Sound does not travel
in vacuum.
Activity:-

Suspend an electric bell in an air tight bell jar. Connect the bell jar to a
vacuum pump. If the switch is pressed, we can hear the sound of the
bell. If air is pumped out through the vacuum pump, we cannot hear
the sound of the bell. This shows that sound needs a medium to travel
and sound cannot travel in vacuum.
Bell jar
Electric bell
Cork

14. CHARACTERISTICS OF A SOUND WAVE
The change in density from one maximum value
to the minimum value and again to the
maximum value makes one complete oscillation.
 The distance between two consecutive
compressions or two consecutive rarefactions is
called the wavelength, λ.
 The time taken by the wave for one complete
oscillation of the density or pressure of the
medium is called the time period, T.
The number of complete oscillations per unit time
is called the frequency (ν), 1/ν = T
The speed v, frequency ν, and wavelength λ, of
sound are related by the equation, v = λν.

15. Reflection of sound Reflection of sound :-:-
Like light, sound gets reflected at the surface of a solid or liquid and
follows the laws of reflection.
i) The angle of incidence is equal to the angle of reflection.
ii) The incident ray, the reflected ray and normal at the point of
incidence all lie in the same plane.
Activity :- Take two pipes of the same length and arrange them on a
table near a wall or metal plate. Keep a clock near the open end of one
pipe and try to hear the sound of the clock through the other pipe by
adjusting the position of the pipe.
Now measure the angles of incidence
and reflection. Then lift the second
pipe and try to hear the sound.
It will be seen that the angle of
incidence is equal to the angle of
reflection. The incident ray, the
reflected ray and normal all lie in
the same plane.

16. ECHOECHO
For hearing a distinct sound, the time
interval between the original sound and the
reflected one must be at least 0.1 s.
The minimum distance of the obstacle from
the source of sound must be 17.2 m. This
distance will change with the temperature of
air.
Echoes may be heard more than once due to
successive or multiple reflections. The rolling
of thunder is due to the successive reflections
of the sound from a number of reflecting
surfaces, such as the clouds and the land.

17. REVERBERATION
The persistence of sound in an auditorium
is the result of repeated reflections of
sound and is called reverberation.

18. USES OF MULTIPLE REFLECTION
OF SOUND
Megaphones or loudhailers, horns, musical
instruments such as trumpets and
shehanais, are all designed to send sound
in a particular direction without spreading
it in all directions.

19. Stethoscope is a medical instrument used
for listening to sounds produced within the
body, chiefly in the heart or lungs. In
stethoscopes the sound of the patient’s
heartbeat reaches the doctor’s ears by
multiple reflection of sound.

20. Range of Hearing
The audible range of hearing for average
human beings is in the frequency range of
20Hz – 20 kHz.

21. Sound waves with frequencies below the
audible range are termed “infrasonic” and
those above the audible range are termed
“ultrasonic”.
Ultrasound has many medical and industrial
applications.
The SONAR technique is used to determine
the depth of the sea and to locate under
water hills, valleys, submarines, icebergs,
sunken ships etc

22. Structure of Human Ear
Human Ear

23. We are able to hear with the help of an
extremely sensitive device called the ear. It
allows us to convert pressure variations in
air with audible frequencies into electric
signals that travel to the brain via the
auditory nerve.

24. Solved Examples:Solved Examples:
1). A person clapped his hands near a cliff and
heard the echo after 5 s. What is the distance
of the cliff from the person if the speed of the
sound, v is taken as 346 m s–1?
Solution:
Given, Speed of sound, v = 346 m s–1 , Time
taken for hearing the echo, t = 5 s ,
Distance travelled by the sound = v × t =
346 × 5 = 1730 m. In 5 s sound has to
travel twice the distance between the cliff
and the person. Hence, the distance between
the cliff and the person = 1730/2 = 865m.

25. 2). A sound wave has a frequency of 2 kHz
and wave length 35 cm. Calculate the speed
of the wave?
Solution:
Given, Frequency, ν = 2 kHz = 2000 Hz
Wavelength, λ = 35 cm = 0.35 m.We know
that speed, v of the wave= λ ν
= 0.35 m × 2000 Hz = 700 m/s.