3. Sound is a type of energy. Sound travels
in the form of wave from one place to
another.

4. Reflection is the change in direction of
a wavefront at an interface between two
different media so that the wavefront
returns into the medium from which it
originated. Common examples include the
reflection of light, sound and water waves.

5. Sound wave also gets reflected as light waves do. Bouncing
back of sound wave from the surface of solid or liquid is
called reflection of sound.
Reflection of sound follows the Laws of Reflection as light
wave does. This means the angle of incident wave and
reflected wave to the normal are equal.
For reflection of sound a polished or rough and big obstacle is
necessary.
Reflection of sound is used in many devices. For example;
megaphone, loudspeaker, bulb horn, stethoscope, hearing
aid, sound board etc.

7. Loudspeaker, Megaphone and bulb horn are devices
used to send the sound in desired direction without
spreading the sound all around. These devices act on
the laws of reflection of sound wave.
In such devices, a funnel like cone shaped tube is
used. Sound is introduced at the narrower end of
tube and let to come out from wider end. Because of
successive reflections, the amplitude of sound is
added up which makes the sound louder. The name
‘Loudspeaker’ is given as it is used to make the sound
louder.

8. Stethoscope: –
Stethoscope is used to hear the sounds of
internal organs of a patient; for diagnostic
purposes. It works on the laws of reflection of
sound.

9. In stethoscope, sound is received
by chest piece and sent to the
earpieces by multiple reflecting
through a long tube. Doctors
diagnose the condition of an organ
of the human body by hearing the
sound using the stethoscope.
Stethoscope has become the
symbol of the medical profession
since its invention.

10. Soundboard –
Sound board is used to send the sound towards
audience in big hall or auditorium. This works on the
basis of laws of reflection of sound waves.
Sound board is a big concave board and is set in such a
fashion behind the stage that speaker is at the focus.
Sound coming from speaker falls over sound board and
gets reflected towards the audience. As a result, the
audience sitting in the hall even at far distance from the
speaker can clearly hear what the speaker is saying.
Additionally, the ceiling of the auditorium is also made
curved so that it also acts like sound board. The curved
surface of the ceiling reflects the sound waves and
facilitates better hearing.

12. The sound which we hear after reflection is
called echo or echo of sound. One can hear the
echo by shouting loudly in a big hall. After
shouting loudly, the same sound reaches the
ears after reflecting from the surface of the
wall. Echo of sound can be heard by producing
sound at place surrounded by hills or big
buildings.
Thus, repetition of sound because of multiple
reflection of sound wave is called echo.

13. You may have heard the echo of your yahoo in
hilly areas. This happens because of multiple
reflection of sound wave and is often called
multiple echoes.

14. The rolling sound of thunder is heard
because of the multiple reflections of
thunder sound or multiple echoes. The
sound of thunder comes to us many times
because of reflections from clouds and earth
surface.

15. (a) In measuring the depth of sea/ocean.
(b) For the detection of the position of any objects, such as
shipwrecks, sea rocks, hidden ice-berg in the sea and
ocean.
(c) Investigating any problem inside the human body.
For above mentioned purposes, sound of high frequency is
produced so that reflections can be received from various
surfaces. The time taken for reception of reflected sound
waves is analyzed by a computer to detect the problem.

16. Ultrasound is an oscillating sound pressure wave with
a frequency greater than the upper limit of the
human hearing range. Ultrasound is thus not
separated from 'normal' (audible) sound by
differences in physical properties, only by the fact that
humans cannot hear it. Although this limit varies from
person to person, it is approximately
20 kilohertz (20,000 hertz) in healthy, young adults.
Ultrasound devices operate with frequencies from
20 kHz up to several gigahertz.

17. A common use of ultrasound is in underwater range finding, this
use is also called Sonar. An ultrasonic pulse is generated in a
particular direction. If there is an object in the path of this pulse,
part or all of the pulse will be reflected back to the transmitter
as an echo and can be detected through the receiver path. By
measuring the difference in time between the pulse being
transmitted and the echo being received, it is possible to
determine the distance.
The measured travel time of Sonar pulses in water is strongly
dependent on the temperature and the salinity of the water.
Ultrasonic ranging is also applied for measurement in air and for
short distances. For example hand-held ultrasonic measuring
tools can rapidly measure the layout of rooms.

18. Ultrasound is used in sonography- looking at human
babies in the mother’s womb. Ultrasound can be used
to work out how old the baby is, determine its
location, find the location of the placenta, determine
the sex of the baby (male or female), check for
heartbeat, check for normal fetal growth and check
for any abnormalities. Note that the results from an
ultrasound are occasionally wrong. Some people are
‘surprised’ when they have a girl after the ultrasound
told them that they would have a boy!

19. In industry, ultrasound is used to determine how thick objects
such as metals and plastic are.
Ultrasound has been shown to work with antibiotics in killing
bacterial cells.
Bacteria, particularly those in sewage, can be disintegrated
(killed) by using ultrasonic waves.
Believe it or not, ultrasound can be used to clean teeth.
Dental hygienists use ultrasound.

21. Sonar (originally an acronym for sound Navigation And Ranging) is a
technique that uses sound propagation (usually underwater, as
in submarine navigation) to navigate, communicate with or detect objects
on or under the surface of the water, such as other vessels. Two types of
technology share the name "sonar": passive sonar is essentially listening
for the sound made by vessels; active sonar is emitting pulses of sounds
and listening for echoes. Sonar may be used as a means of acoustic
location and of measurement of the echo characteristics of "targets" in the
water. Acoustic location in air was used before the introduction of radar.
Sonar may also be used in air for robot navigation, and SODAR (an upward
looking in-air sonar) is used for atmospheric investigations. The
term sonar is also used for the equipment used to generate and receive
the sound. The acoustic frequencies used in sonar systems vary from very
low (infrasonic) to extremely high (ultrasonic). The study of underwater
sound is known as underwater Aoustics or Hydroacoustics.

23. Sonar has many uses. Passive sonar is used by the
navy to find ships and submarines. Scientists use it to
find whales or other animals in the sea they want to
study. Active sonar is used to measure distance with
sound. When sound hits an object, some of the sound
waves are reflected back to the device. The distance
to the object can be found from the time it takes for
the sound to travel to the object and back.