Sound bounces turn off a hard or a liquid choose a rubber round bounces turn off a wall. Prefer light, sound it s okay reflected in ~ the surface of a hard or liquid and also follows the same regulations of reflection as you have actually studied in previously classes. The direction in i m sorry the sound is incident and also is reflected do equal angles v the regular to the reflecting surface in ~ the allude of incidence, and also the three room in the very same plane. An problem of big size which may be refined or rough is essential for the reflection of sound waves.

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• take it two similar pipes, as displayed in Fig. 12.11. You can make the pipes using chart paper. The length of the pipes must be sufficiently lengthy as shown.• Arrange castle on a table close to a wall.• store a clock near the open finish of among the tube and shot to listen the sound of the clock through the various other pipe.• change the place of the tube so that you can best hear the sound that the clock.• Now, measure the angles of incidence and reflection and see the relationship between the angles.• background the pipe on the ideal vertically to a little height and observe what happens.



If us shout or clap close to a suitable reflecting thing such as a tall structure or a mountain, we will certainly hear the very same sound again a little later. This sound which us hear is called an echo. The emotion of sound stubborn in our brain for around 0.1 s. Come hear a distinctive echo the moment interval in between the initial sound and also the reflected one should be at the very least 0.1s. If we take the speed of sound to be 344 m/s at a given temperature, say at 22 ºC in air, the sound have to go to the obstacle and also reach ago the ear of the listener ~ above reflection after ~ 0.1s. Hence, the total distance extended by the sound native the point of generation come the reflecting surface and earlier should it is in at least (344 m/s) × 0.1 s = 34.4 m. Thus, for hearing unique echoes, the minimum distance of the problem from the resource of sound have to be half of this distance, the is, 17.2 m. This street will readjust with the temperature of air. Echoes may be heard more than once because of successive or lot of reflections. The rolling of thunder is as result of the successive reflections the the sound native a variety of reflecting surfaces, such together the clouds and also the land.


A sound created in a large hall will certainly persist by repetitive reflection from the walls till it is decreased to a value where it is no much longer audible. The repetitive reflection that outcomes in this persistence that sound is called reverberation. In one auditorium or huge hall too much reverberation is extremely undesirable. To reduce reverberation, the roof and also walls that the auditorium are usually covered v sound-absorbent products like compressed fibreboard, rough plaster or draperies. The seat products are likewise selected on the communication of their sound taking in properties.


A human clapped his hands close to a cliff and also heard the echo after ~ 5 s. What is the street of the cliff from the human if the speed of the sound, v is taken together 346 m s–1?

Solution:Given,Speed of sound, v = 346 m s–1Time taken because that hearing the echo,t = 5 sDistance took trip by the sound= v × t = 346 m s–1 × 5 s = 1730 mIn 5 s sound has to travel double the distance between the cliff and the person. Hence, the distance in between the cliff and the person= 1730 m/2 = 865 m.


1. An echo changed in 3 s. What is the distance of the showing surface native the source, provided that the rate of sound is 342 m s–1?

Uses of many reflection of sound

Megaphones or loudhailers, horns, musical instruments such as trumpets and shehanais, room all designed to send sound in a particular direction without spreading it in every directions, In these instruments, a tube adhered to by a conical opening shows sound successively to guide most that the sound waves from the resource in the forward direction towards the audience.

Stethoscope is a medical instrument offered for listening come sounds created within the body, chiefly in the love or lungs. In stethoscopes the sound of the patient’s heartbeat get the doctor’s ears by lot of reflection of sound,

Generally the ceilings of concert halls, conference halls and also cinema halls room curved so that sound after ~ reflection reaches every corners the the hall, periodically a curved soundboard may be put behind the stage so the the sound, after mirroring from the sound board, spreads evenly throughout the width of the hall

Range the Hearing

The audible variety of sound for humans extends from about 20 Hz to 20000 Hz (one Hz = one cycle/s). Youngsters under the period of five and some animals, such as dogs can hear approximately 25 kHz (1 kHz = 1000 Hz). As civilization grow older your ears come to be less sensitive to higher frequencies. Sound of frequencies below 20 Hz are called infrasonic sound or infrasound. If we can hear infrasound we would certainly hear the vibrations the a pendulum just as we hear the vibrations the the wing of a bee. Rhinoceroses interact using infrasound of frequency together low together 5 Hz. Whales and also elephants produce sound in the infrasound range. That is observed the some pets get disturbed prior to earthquakes. Earthquakes develop low-frequency infrasound prior to the key shock waves start which probably alert the animals. Frequencies higher than 20 kHz are called ultrasonic sound or ultrasound. Ultrasound is produced by dolphins, bats and also porpoises. Moths of details families have an extremely sensitive hear equipment. This moths have the right to hear the high frequency squeaks the the bat and also know once a bat is flying nearby, and also are able come escape capture. Rats additionally play games by developing ultrasound.


1. What is the audible range of theaverage human being ear?2. What is the range of frequenciesassociated with(a) Infrasound?(b) Ultrasound?

Applications that Ultrasound

Ultrasounds room high frequency waves. Ultrasounds space able to travel along welldefined paths also in the existence of obstacles. Ultrasounds are used broadly in industries and also for medical purposes.

• Ultrasound is typically used come clean parts located in hard-to-reach places, for example, spiral tube, odd shame parts, electronic contents etc. Objects to be cleaned are put in a cleaning solution and also ultrasonic waves room sent right into the solution. As result of the high frequency, the corpuscle of dust, grease and also dirt acquire detached and also drop out. The objects thus acquire thoroughly cleaned.• Ultrasounds deserve to be provided to finding cracks and flaws in steel blocks. Metallic contents are generally used in construction of big structures like buildings, bridges, machines and also scientific equipment. The crack or holes within the metal blocks, which room invisible from external reduces the toughness of the structure. Ultrasonic waves are permitted to pass v the metal block and also detectors are used to detect the transmitted waves. If there is even a little defect, the ultrasound it s okay reflected earlier indicating the existence of the flaw or defect, as shown in Fig


Ordinary sound of much longer wavelengths cannot be offered for such purpose as it will certainly bend approximately the corners the the defective location and also enter the detector

• Ultrasonic waves are made come reflect from miscellaneous parts of the heart and form the picture of the heart. This method is referred to as ‘echocardiography’.• Ultrasound scanner is an tool which supplies ultrasonic tide for acquiring images of interior organs of the human body. A doctor may image the patient’s guts such as the liver, gall bladder, uterus, kidney, etc. It help the physician to recognize abnormalities, such as stones in the gall bladder and also kidney or tumours in various organs. In this an approach the ultrasonic waves travel through the organization of the body and get reflect from a region where there is a adjust of organization density. These waves space then converted into electric signals that are supplied to generate pictures of the organ. These pictures are then displayed on a monitor or published on a film. This an approach is referred to as ‘ultrasonography’. Ultrasonography is likewise used for examination that the foetus during pregnancy to detect congenial defects and also growth abnormalities.• Ultrasound might be employed to break small ‘stones’ formed in the kidneys into fine grains. This grains later on get purged out v urine.


The acronym SONAR represents SOund Navigation and Ranging. Sonar is a device that supplies ultrasonic waves to measure the distance, direction and also speed the underwater objects. Exactly how does the sonar work? Sonar consists of a transmitter and a detector and also is set up in a watercraft or a ship, as presented in Fig.


The transmitter produces and also transmits ultrasonic waves. These waves travel with water and also after to mark the object on theseabed, gain reflected back and space sensed by the detector. The detector counter the ultrasonic waves into electrical signals i beg your pardon are appropriately interpreted. The distance of the object the reflected the sound wave deserve to be calculated by learning the rate of sound in water and the time interval between transmission and also reception that the ultrasound. Let the moment interval in between transmission and also reception of ultrasound signal it is in t and the speed of sound through seawater be v. The complete distance, 2d took trip by the ultrasound is then, 2d = v × t.

The above technique is dubbed echo-ranging. The sonar method is offered to determine the depth the the sea and also to locate underwater hills, valleys, submarine, icebergs, sunken ship etc.


A ship sends out out ultrasound the returns indigenous the seabed and also is detected after 3.42 s. If the speed of ultrasound through seawater is1531 m/s, what is the distance of theseabed native the ship?Solution: Given, Time in between transmission anddetection, t = 3.42 s.Speed of ultrasound in sea water, v = 1531 m/sDistance took trip by the ultrasound = 2 × depth the the sea = 2dwhere d is the depth the the sea.2d = speed of sound × time = 1531 m/s × 3.42 s = 5236 m d = 5236 m/2 = 2618 m.Thus, the distance of the seabed native the delivery is 2618 m or 2.62 km.

Structure of human being Ear

How perform we hear? We are able come hear with the aid of an extremely sensitive an equipment called the ear. It allows us to convert pressure variations in air through audible frequencies into electric signals that take trip to the brain via the hear nerve. The auditory facet of human ear is discussed below.


The outer ear is dubbed ‘pinna’. It collects the sound from the surroundings. The accumulated sound passes through the hear canal. In ~ the end of the hear canal over there is a slim membrane dubbed the ear drum or tympanic membrane. As soon as a compression the the tool reaches the eardrum the pressure on the outside of the membrane increases and forces the eardrum inward. Similarly, the eardrum moves outward as soon as a rarefaction will it. In this means the eardrum vibrates. The vibrations are intensified several times by three bones (the hammer, anvil and also stirrup) in the middle ear. The center ear transmits the amplified pressure variations received from the sound wave to the within ear. In the inner ear, the pressure variations room turned into electrical signals by the cochlea. These electrical signals are sent to the brain via the hear nerve, and also the mind interprets them as sound.

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What you have learnt

• Sound is created due to vibration of different objects.• Sound travels together a longitudinal wave v a material medium.• Sound travels as succeeding compressions and also rarefactions in the medium.• In sound propagation, the is the energy of the sound the travels and also not the particles of the medium.• Sound cannot take trip in vacuum.• The adjust in thickness from one maximum value to the minimum value and again to the preferably value renders one finish oscillation.• The distance in between two continuous compressions or 2 consecutive rarefactions is dubbed the wavelength, λ.• the moment taken by the tide for one complete oscillation the the density or push of the medium is dubbed the time period, T.• The number of complete oscillations every unit time is referred to as the frequency (ν),1/T.• The rate v, frequency ν, and also wavelength λ, that sound are connected by the equation, v = λν.• The rate of sound depends mainly on the nature and the temperature the the transmitting medium.• The regulation of have fun of sound says that the directions in i beg your pardon the sound is incident and also reflected do equal angles withthe common to the showing surface at the allude of incidence and the 3 lie in the very same plane.• because that hearing a distinct sound, the time interval between the initial sound and the reflected one must be at the very least 0.1 s.• The persistence of sound in one auditorium is the an outcome of repetitive reflections of sound and also is dubbed reverberation.• Sound nature such as pitch, loudness and quality are figured out by the corresponding wave properties.• Loudness is a physiological response of the ear to the intensity of sound.• The lot of sound energy passing each second through unit area is referred to as the soot of sound.• The audible variety of hearing because that average human beings is in the frequency selection of 20 Hz – 20 kHz.• Sound waves v frequencies below the audible range are termed “infrasonic” and also those over the audible selection aretermed “ultrasonic”.• Ultrasound has many medical and industrial applications.• The SONAR an approach is offered to identify the depth that the sea and also to find under water hills, valleys, submarines, icebergs, sunken pearls etc.