1. Sound is a form of energy that travels as longitudinal waves through air and other materials. Sources of sound vibrate and transmit the sound waves. 2. Sound waves travel through the air and are detected by our ears. They can be reflected, refracted, or diffracted as they travel. 3. Ultrasonic waves with frequencies above human hearing are used for applications like medical imaging and motion sensors. They can be detected electronically.

2. 1. Sound is a form of energy (as the damage from
supersonic booms shows) which travels as a progressive
wave, but of a type called longitudinal.
2. Sources of sound all have some part that vibrates.
Example:
3. The sound travels through the air to our ears and we
hear it.
4. Sound waves shows the Refraction, Reflection
and Diffraction effects.
● Origin and
transmission
of sound

3. Longitudinal
waves
Figure 33.3. Compressions C (where the coils
are closer together) and rarefactions R (where
the coils are further apart) travel along
the spring.

4. Sound waves A sound wave, produced for example by a
loudspeaker, consists of a train of compressions
(‘squashes’) and rarefactions (‘stretches’) in the
air

5. Audible
frequency of
sound

6. Reflection and
echoes
 Sound waves are reflected well from hard, flat surfaces
such as walls or cliffs and obey the same laws of
reflection as light.The reflected sound forms an echo.
 If the reflecting surface is nearer than 15m from the
source of sound, the echo joins up with the original
sound which then seems to be prolonged.This is called
reverberation.
Example: Some is desirable in a concert hall to stop it
sounding ‘dead’, but too much causes ‘confusion’.
Link for the difference between Echo and Reverberation
https://www.khanacademy.org/science/in-in-class9th-physics-india/in-in-sound-
india/in-in-reflections-echoes-and-reverberation/v/echoes-and-reverberations

7. ●Speed of sound
 The speed of sound depends on the material through which it is
passing
 It is greater in solids than in liquids or gases because the molecules
in a solid are closer together than in a liquid or a gas.
 In air the speed increases with decrease in temperature and at low
altitudes (due to density change), speed is less at high altitude
than at sea level. Changes of atmospheric pressure do not affect
it.
 speed of sound in air = 2d
t

8. Practice
Problems

9. Practice
Problems

10. ● Musical notes
Linkfortheoscilloscope
https://academo.org/demos/vi
rtual-oscilloscope/
 Irregular vibrations such as those of motor engines cause noise; regular
vibrations such as occur in the instruments of a brass band, produce musical
notes which have three properties
 Pitch,
The pitch of a note depends on the frequency of the sound
A high-pitched note has a high frequency and a short wavelength
 Loudness
A note becomes louder when more sound energy enters our ears per second
than before.
This will happen when the source is vibrating with a larger amplitude.
 Quality.
 The quality or timbre of sound is that characteristic which enables us to
distinguish one sound from another having the same pitch and loudness.

11. Thesamenoteondifferent
instruments soundsdifferent; we
saythenotesdiffer inqualityor
timbre.Thedifference arises
becausenoinstrument(excepta
tuningforkandasignalgenerator)
emitsa‘pure’note,i.e.ofone
frequency.Notesconsistofamain
orfundamental frequencymixed
withothers,calledovertones,which
areusuallyweakerandhave
frequencies thatareexactmultiples
ofthefundamental.Thenumber
andstrengthoftheovertones
decides thequalityofanote.A
violinhasmoreandstrongerhigher
overtonesthanapiano.

12. ULTRASONICS
Ultrasonic
echo
techniques
 Sound waves with frequencies above 20kHz are called ultrasonic waves; their
frequency is too high to be detected by the human ear but they can be detected
electronically and displayed on a CRO
 Ultrasonic waves are produced by a quartz crystal which is made to vibrate
electrically at the required frequency
Ultrasonic echo techniques
 A bat emitting ultrasonic waves can judge the distance of an object from the time
taken by the reflected wave or ‘echo’ to return.
 Ships with sonar can determine the depth of a shoal of fish or the sea bed
 Motion sensors also work on this principle.
 In medical ultrasound imaging, used in antenatal clinics to monitor the health of
an unborn baby
Other Uses
 Ultrasound can also be used in ultrasonic drills to cut holes of any shape or size in
hard materials
 ultrasonic vibrator are used to wash jewelry and lampcovers.

13. Seismic waves
 Earthquakes produce both longitudinal waves (P-waves) and
transverse waves (S-waves) that are known as seismic waves.
These travel through the Earth at speeds of up to 13 000 m/s.

14. Practice
Problem

15. Practice problems.