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

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

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.

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.

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.

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.

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.

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.

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.

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.

(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.

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.

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.

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!

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.

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.

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.