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Question: 1
Q (6) What do you know understand by the longitudinal wave? Describe the Longitudinal nature of sound waves?
Answer: 1
1-50Part (A)
Longitudinal Waves:
The longitudinal waves the particles of the medium vibrate Paralled to the direction of propogation of wave e.g sound wave.
Nature of sound:
Sound waves are compressional in nature which can explained by following experiment when we strike the tuning fork on rubber , pad its prongs with begin to move between position AOB When prongs move from O to B , The exert pressure on the adjacent layer of air and compression is produced. The compressed layer of air is compress the layer of air next t it and so when prongs move from B to A , the pressure on layer of air is decreased and rare faction is produced. This rare faction is transferred to the air layer next to it and so on. So when the tuning fork moves back and forth rapidly, a series of compression and rare faction is produced due t which sound waves propagate through air. As the direction of sound wave is along the direction of oscillating air molecules, it shows that sound wave is compressional in nature.
Y /AOB= IIIIIIIIIIIIIIIII vibrate of tuning fork
Y/OB = IIIIIIIIIIIIIIIII after striking with a rubber hammer
Y/AD = IIIIIIIIIIIIIIII
Wavelength:
Distance between two consecutive compressions or rare faction is the wave length of sound waves it is donated by λ.
Question: 2
A normal conservation involves sound intensities of about 3.0*10-6 Wm-2.What is the decibel level for this intensity?
Answer: 2
2-50Part (B)
Given data:
Intensities of sound = I=3*10-6Wm-2
Threshold intensity = Io =10-12 Wm-2
Solution:
We know that:
L-Lo= Lo I/I db
= 10 log(3*10-6)db
(10-12)
= 10 log (3*10-6 *10-12)db
= 10 log (3*10/6)db
= 10 (log 3+ log 10/6)db
= 10 (0.477+6 log/10)db
= 10 ( 0.477 +6) db
= 10 *6.477
= 64.77 db
L-Lo= 64.8 db
Question: 3
<div>Explain the characteristic of sound?</div><div><br></div>
Answer: 3
3-50Part (A)
The characteristic of sound through which a loud and a faint sound can be distinguished is called loudness. The loudness of sound depend upon the amplitude of the vibrating body area of vibrating body. Distance from vibrating body.
Pitch of Sound:
The characteristic of sound by which a shrill sound can be distinguished from a grave sound is called pitch.
Quality of sound:
The characteristic of sound by which two sounds of same
loudness and pitch are distinguish from each other iss called quality a sound.
Example:
If in a room a note of given loudness and pitch is sounded on flute and also on a piano, we can distinguish between them by standing even outside the room, because quality of these notes is different.
Intensity
of sound:
Sound energy following per second through a unit area held perpendicular to the direction of sound wave is called intensity of sound.
Unit:
Its unit is Walt per square meter Wm-2.It is a physical quantity and can be measured accurately.
Question: 4
A sound waves has a frequency of 2kHz and wave length 35cm.How long will it take to travel 1.5km?
Answer: 4
4-50Part
(B)
Frequency = f= 2kHz
= 2*1000Hz
= 2000 Hz
Wavelength
= λ=35cm
= 35/100 m
= 0.35 m
Distance = s= 1.5 km
= 1.5*1000 m
=1500 m
Time = t=?
Solution:
We know that
V = f λ
= 2000*0.35
= 2000 * 35/100
= 20*35
= 700 ms1
We
also know that
S = v*t
1500 = 700*t
T = 1500/700
T = 2.1s
Question: 5
<span style="font-size:11.0pt;line-height:115%;
font-family:"Calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:
Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin;
mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi;
mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">What
is sound wave?</span>
Answer: 5
5-50Sound is a form of energy that is passed from one to another in the form of long dinal waves sound is produced a vibrating body.
Question: 6
<span style="font-size:11.0pt;line-height:115%;
font-family:"Calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:
Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin;
mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi;
mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">What
is tunning fork?</span>
Answer: 6
6-50Tunning fork is a device that we use to produce a particular sound if we strike the tunning fro against rubber hammer the tunning fork will begin to vibrate and produced a sound by it.
Question: 7
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font-family:"Calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:
Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin;
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mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">What
is tunning fork?<br>
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Answer: 7
7-50Tunning fork is a device that we use to produce a particular sound if we strike the tunning fro against rubber hammer the tunning fork will begin to vibrate and produced a sound by it.
Question: 8
<p class="MsoNormal">Define longitudinal waves?</p>
Answer: 8
8-50In longitudinal or compressional waves the particles of the medium vibrate parallel to the direction of propagation wave.
For example: sound wave.
Question: 9
<p class="MsoNormal">Define loudness?</p>
Answer: 9
9-50Loudness is the characteristics of sound by which loud and faint sounds can be distinguished.
Question: 10
<p class="MsoNormal">Define Amplitude?</p>
Answer: 10
10-50The maximum displacement of a vibrating body on either side from its mean position is called its amplitude.
Question: 11
<p class="MsoNormal">Define pitch and quality?</p>
Answer: 11
11-50Pitch is the characteristic sound by which we can distinguish between a shrill and a grave sound.
Quality: The characteristic of sound by which we can distinguish between two sound of same loudness and pitch is called quality.
Question: 12
<p class="MsoNormal">Is speed of sound more in solids or liquids and why?</p>
Answer: 12
12-50Speed of sound in solids is more then in liquids because the solids atoms are closely packed whereas molecules of liquids are for a part.
Question: 13
<p class="MsoNormal">We can recognize person speak with the same loudness from
their voice how is this possible?</p>
Answer: 13
13-50We can recognize person speaking with some loudness from their voice because sound waves have different waves forms so their quality is different and we can distinguished them from each other.
Question: 14
<p class="MsoNormal">What is intensity of sound?</p>
Answer: 14
14-50Sound energy passing per second through a unit area held perpendicular of sound waves is called intensity of sound. the unit of intensity of sound is unit per square metre (Wm-2)
Question: 15
<p class="MsoNormal">What is bell and zero bell?</p>
Answer: 15
15-50If intensity I of any unknown sound is 10 times greater than the intensity Zo of the faintest audible sound i.e I =10 I0 is called bell
Zero bell: Faintest audible sound having intensity 10-12 WM-2 is called reference intensity or zero bell
Question: 16
<p class="MsoNormal">What is intensity level?</p>
Answer: 16
16-50Difference (L-LO) between the loudness L of an unknown sound and the loudness Lo is called the intensity level sound level of the unknown sound.
L- Lo=10 log ( I/Io) (db)
Question: 17
<p class="MsoNormal">How can depth of sea be measured by ultrasonic?</p>
Answer: 17
17-50Ultrasound is used to locate under water depths or is used for locating objects lying deep on the ocean floor etc,the techniques is called sonar the sound waves are send from a transmitter and receiver collects the reflected sound the time lopse is calculated knowing the speed of sound in water the distance of the object from the ocean surface can be estimated.
Question: 18
<p class="MsoNormal">What is decibel scale?</p>
Answer: 18
18-50The decibel scale is a logarithmic measure of the amplitude of sound waves.
Question: 19
<p class="MsoNormal">Is there any difference between echo and reflection of sound
explain?</p>
Answer: 19
19-50When sound is incident on the surface of a medium it bounces back into the first medium this phenomena is called echo or reflection of sound there is no difference between echo reflection of sound.
Question: 20
<p class="MsoNormal">What is speed of sound through brass and iron at 25 <b>°C?<o:p></o:p></b></p>
Answer: 20
20-50Speed of sound at 25
°C through bra is 4700ms-1 and through
iron is 5950ms-1.
Question: 21
<p class="MsoNormal"><b>What is the
difference between frequency and pitch?<o:p></o:p></b></p>
Answer: 21
21-50Frequency is the
number of waves passing through a point in one second
Pitch: pitch is
characteristic of sound due to which we can distinguish between shrill and grave sound.
Question: 22
<p class="MsoNormal"><b>Why ultrasound is useful
in medical field?<o:p></o:p></b></p>
Answer: 22
22-50Ultrasound is useful
in medical field and higher frequency (v=fr) with very small wave lengths than
audible sound waves.
Question: 23
<p class="MsoNormal"><b>On which factors does
the loudness of sound depend ?<o:p></o:p></b></p>
Answer: 23
23-50Loudness of sound
depends the following factors the amplitude of the vibrating body area of
vibrating body distance from vibrating body.
Question: 24
<p class="MsoNormal"><b>What is musical
sound?<o:p></o:p></b></p>
Answer: 24
24-50Such sounds which has
pleasant effect on our ears are called musical sounds.
Question: 25
<p class="MsoNormal"><b>What is noise?<o:p></o:p></b></p>
Answer: 25
25-50The sound with
jarring effect on our ears are called noise.
Question: 26
<p class="MsoNormal"><b>Define acoustic protection
?<o:p></o:p></b></p>
Answer: 26
26-50The technique or
method used to absorb undesirable sound energy by soft and porous surfaces is called acoustic protection.
Question: 27
<p class="MsoNormal"><b>Define audible
frequency range?<o:p></o:p></b></p>
Answer: 27
27-50The range of the
frequencies which a human ear can hear is called the audible frequency range.
Question: 28
<p class="MsoNormal"><b>What is the audible
frequency range for human ear?<o:p></o:p></b></p>
Answer: 28
28-50A normal human ear
can hear sound only if its frequency lies between 20Hz and 20,000 Hz a human ear can oscillate
back and forth up to 20,000 times in one second .
Question: 29
<p class="MsoNormal"><b>Will two
separate 50db sounds together constitude
a 100db sounds?<o:p></o:p></b></p>
Answer: 29
29-50Since db is the unit
of sound level and its value depend upon the log of intensities therefore 50db
sound from two bodies does not constitute 100db sound each 10db increase in
sound makes the sound 10-times louder.
Question: 30
What is speed of sound?
Answer: 30
30-50The speed of sound is the distance traveled per unit time by a sound wave as it propagates through a medium. Sound, like all waves, travels at a certain speed and has the properties of frequency and wavelength. At 20 °C, The speed of sound in air is 343 m/s. Sound depends on the material through which it is passing.
Children at play may discover that sound travels very easily along a metal fence. Swimmers notice that they can hear a distant motorboat better with their ears under the water than in the air.In both examples, sound is traveling in a material other than air. You may have watched distant lightning and noticed the time lapse before the sound of thunder reaches you. This is an example of the compared to the speed of light. The speed of sound in water is almost five times faster than its speed in air. Sound travels most rapidly in certain solids, less rapidly in many liquids, and quite slowly in most gases. The speed of sound `v' can be found by dividing distance `S' by time `t' as :
Speed = distance/time
or v= S/t
Question: 31
<div>Describe the terms loudness, pitch and quality. Explain each by giving an example.</div><div><br></div>
Answer: 31
31-50Pitch:
Pitch distinguishes shrill sound from grave sound. The Pitch of a note depends on the frequency of the sound wave reaching the ear. A high-pitched note has a high frequecny and a short wavelength. A Low pitched note has a low frequency and a long wavelength.
Support a bicycle on its stand and rotate its rear wheel. Hold a piece of cardboard in your hand with its free end touching the spikes of the rotating wheel. The sound will be produced , as you increased the speed of rotation the spokes touching per unit time to the cardboard will increase, which will increase the frequency. As a result, sound produced will become shriller (of a higher pitch).
Question: 32
<div>Describe the terms loudness, pitch and quality. Explain each by giving an example.</div><div><br></div>
Answer: 32
32-50Loudness:
The greater the sound energy , the louder is the sound. The loudness depends upon the amplitude (height of the sound wave .
Loudness depends upon the following factors:
The Area Of Vibrating Body:
Larger the area of vibration larger will be amplitude fo sound produced.
Distance From The Source Of Sound:
The farther away, the smaller the amplitude.
Material Through Which Sound Is Traveling:
Amplitude of sound wave is different in different materials such as water and air.
For example , a drum produces loud sound if its membrane is struck strongly. This is because the vibrating body starts to oscillate with larger amplitude and therefore the sound it produces also has a larger amplitude and as a result the sound is louder.
Question: 33
What is intensity level? Describe the decibels scale for the intensity of different sound levels.
Answer: 33
33-50Intensity level:
An average human ear can detect sounds with an intensity as low as 10-12W/m2 and as high as 1 W/m2 (
and even higher, although above this, it is painful). This is an incredibly wide range of intensity, spanning a factor of 1012from lowest to highest. To permit comparison of values which vary so greatly in magnitude, it is most convenient to express them in terms of their logarithms- the power to which 10 must be raised to equal the number.
if L the loudness and I is the sound intensity in W/m2, then mathematically
L α logI or L= klogI eq (1)
Where `k' is the constant of proportionality. if `Lo' represents the loudness of faintest audible sound of intensity `Io' such that Io = 10-12 W/m2 equation 1 can be written as :
Lo = klogIo eq (2)
Subtracting euation 2 from eq 1 we get
L-Lo= klogI- klogIo or L-Lo = K(logI-KlogIo)
L-L= KlogI/Io
The difference between the loudness fo these two loudness of sound (L-L) is called intensity level or intensity level (ß) and is given as
ß= klogI/Io eq (3)
Since ß is defined in terms of a similar quantities ratio, it sis unit-less, The value of k depends not only on the units of I and Io but also on the unit intensity level. If the intensity of any sound is ten times greater then the intensity Io of the faintest audible sound (I=10 Io), then intensity level of such a sound is taken as unit called bel and value of k becomes 1.Substituting k= 1 equation 3 becomes
ß = log I/Io (bels)
Question: 34
What is noise ? Explain why noise is nuisance?
Answer: 34
34-50Noise:
The excessive displeasing sound which disrupts the balance or activity of human or other living things is called noise
The first type of noise pollution involves noises that are so loud they put the sensitive parts of the ear. Prolonged exposure to sounds of about 85 dB can begin to damage hearing irreversibly. Certain sounds above 120dB can cause immediate damage.
The sound level produced by a jet engine from a few meters away is about 140 dB. The workers working in noisy areas like an airport use headphones to prevent the hearing loss brought on by damage to the inner ear.
The second kind of noise pollution involves noises that are considered annoyances, these sounds are irritating and sometimes becomes intolerable. Studies have found that long-term exposure to noise can cause potentially severe health problems in addition to hearing loss, especially for young children. Constant levels of noise (even at low levels) can be enough to cause stress, which can lead to high blood pressure, insomnia, and psychiatric problems, and can even impact memory and thinking skills in children.
Animals and plants are also victims of noise pollution, it is observed that in animals it damages the nervous system and reproductive system. While in plants growth defects are observed. The World Health Organization has recommended that noise during sleep should be limited to a level of 35dB.
Question: 35
What is sound ? How it is produced, transmitted and received ?
Answer: 35
35-50Sound waves are longitudinal waves traveling through a medium, such as air.Sound wave is created by a vibrating object, such as a guitar string, the human vocal cords, or the diaphragm of a loudspeaker. Moreover, sound can be transmitted only in a medium , such as a gas, liquidm or solid. As we will see, the particles of the medium must be present for the creation fo disturbance and the sound wave to move from place to place. Sound cannot exist in a vacuum.
For example, consider a tuning fork, a common device for producing pure musical notes. A tuning fork consists of two metal prongs, or tines, that vibrate when struck. Their vibration disturbs the air near them
Question: 36
What is audible frequency range?
Answer: 36
36-50There are both upper and lower limits to the sound frequencies that humans can hear. A healthy young person can typically heat frequencies in a range from about 20 Hz (Recall that cycle per second) to 20000Hz (20kHz). The upper limit decreases with age.
Physicists have established a three-part classification of sound, based on the range of human hearing. Sound frequencies lower than 20 Hz are referred to as infrasonic, those in the 20 Hz to 20000 Hz range are audible, and those higher than 2000 Hz are ultrasonic .Different animal have varying hearing ranges. you may have experienced a dog whistle that seems to produce no sound at all when blown, but still brings your pet dog back .
The frequency of the sound produced by these whistles is higher than 20 kHz. While it is outside the audible range for humans, it is obviously not outside the audible range for dogs. The top of a dog's hearing range is about 45 kHz, while a cat's is 64 kHz.
Question: 37
Whart is acoustic protection ? Why is it important?
Answer: 37
37-50Acoustiv protection:
Acoustic protection is the application of soft and porous material to protect individuals against undesirable sounds and noises. Acoustic protection is employed not only for physical health, but for psychological well being as well. Animals and birds have also been reported to express discomfort due to higher noise and sound levels. Acoustic protection is also necessary to minimize stress levels generated due to high noise. Acoustic protection may also bel required to protect structures against vibrations generated by objects, such as trains and earthquakes. This is also required to control the noise generated during construction and / or development activities.
Question: 38
Define sound and prove that sound is produced by vibrating body?
Answer: 38
38-50Sound: sound is a form of energy produced by vibration of bodies and travle in form of pressure waves from one place to the another.
Question: 39
Prove that sound requires material medium for its propagation?
Answer: 39
39-50Sound require material for its propagation: unlike light waves which are electromagnetic in nature and can also pass through vacuum, sound waves require some material medium for their propagation.
Proof; this can be proved by bell jar apparatus. The ball jar is placed on the platform of a vacuum pump. An electric bell is suspended in the bell jar with the help of two wires connected to a power supply.
Question: 40
Describe longitudinal nature of sound waves
Answer: 40
40-50Longitudinal nature of sound waves: propagation of sound waves produced by vibrating tuning fork can be understand by a vibrating tuning fork. Before the vibration of tuning fork, density of air molecules on the right side is uniform. When the right prong of tuning fork moves from mean position , it exerts some pressure on the adjacent layer of air molecules and produces a compression.
this compressed air layer in turn compresses the layer next to it and so on. A moment later , the prong beings to move .
Now the pressure in the adjacent layer decreases and a rarefaction is produced. This rarefaction is transferred to the air layer next to it and so on. As the tuning for moves back and fort rapidly , a series of compressions and rarefactions are created in the air. In this way, sound wave propagates through the air.
As in the direction of propagation of sound wave is along the direction of oscillating air molecules. This shows the longitudinal nature of sound waves. Distance between two consecutive compressions or rarefactions is the wavelength of sound wave.
Question: 41
Write a note on characteristics of sound?
Answer: 41
41-50Characteristics of sound:
- Loudness; loudness is the characteristics of sound by which loud and faint sounds can be distinguished.
- Amplitude of vibrating body: the loudness of sound varies directly with amplitude of vibrating body. The sound produced by a sitar will be loud if we pluck its wires more violently. Similarly, when we beat a drum forcefully amplitude of its membrane increases and we hear loud sound.
Example: sound produced by large drum is louder than small one because of its larger area. If we strike tuning fork on a rubber pad, a fable sound will be heard. But if tuning fork is strike on bench, we will hear loud sound.
Conclusion: we conclude that loudness increase with vibrating area.
Question: 42
Define intensity and find the intensity level in decibel?
Answer: 42
42-50Intensity: " sound energy passing per second through a unit area held perpendicular to the direction of propagation of sound waves is called intensity of sound".
Units: Wm-2, Js-1 m-2
Sound intensity level; the human ears responds to intensities ranging from 10-12 Wm-2 to more than 1 Wm-2. because range is so wide intensities are scaled by factor 10. The barely audible and faintest sound intensity called zero bell and taken as reference intensity.
The loudness of sound also depends on intensity of sound and the physical condition of ear.
Decibel scale; we can construct a scale for measuring intensity level of sound, such scale is known as decibel scale.
Question: 43
Explain Reflection(Echo) of sound?
Answer: 43
43-50When sound is incident on the surface of a medium it bounces back into the first medium. This phenomenon is echo or reflection of sound.
persistence if sound: the sensation of sound persists in our brain for about 0.1 sec. To hear a clear echo, the time interval between our sound and the reflected sound must be least 0.1 sec.
If we consider speed of sound to be 340 ms-1 at a normal temperature in air, we will hear the echo after 0.1 sec.
Production of echo; the total distance covered by the sound from the point point of generation the point of generation to the reflection surface and back should be at least 340ms-1 * 0.1= 34 m.
Thus , for hearing distinct echoes, the minimum distance of the obstacles from the source of sound must be half to this distance, that is 17m echoes may be heard more than once due to successive or multiple reflections.
Activity: take tow identical plastic pipes of suitable length. ( we can make the pipe using chart paper).
- Arrange the pipes on a table near a wall.
- Place a clock near the open end of one of the pipes and try to hear the sound of the clock through the other pipe.
- Adjust the position of the pipes so that you can hear the sound o the clock clearly.
- Now , measure the angle of incidence and reflection and see the relationship between the angles.
- Lift the pipe on the right vertically to a small height an observe what happens.
Question: 44
Explain speed of sound?
Answer: 44
44-50Speed of sound: " sound waves can be transmitted only by any medium containing particles that can vibrate . It cannot pass through vacuum."
Nature of medium will affect the speed of sound waves as
Speed of sound in liquid: speed of sound in liquid is five times that in gasses
vl= 5*va
Speed of sound in air; speed of sound in air is 343ms-1 at one atmospheric pressure and room temperature(21oC)
Speed of sound in solid: speed of sound in solid is fifteen times that in gases
vs=15* va
va= speed of sound in air
vs= speed of sound in solid
vl= speed of sound in liquid
Question: 45
How we can measure speed of sound by Echo method?
Answer: 45
45-50Measuring speed of sound by Echo method;
Apparatus: measuring tape, stop watch, flat wall that can produce a good echo
Procedure;
- use the tape to measure a distance of 50 meters from the wall.
- Now clap your hands in front of the wall at a distance of 50 meters and check if you can clearly hear an echo from the wall. Make sure the echo is not coming from any other wall in the area. The time taken by the sound to travel 10 meters is the time difference between the clap and the echo.
- Now restart the clapping and start the stop watch at the first clap. Count the number of claps , and stop the clapping and the stop watch when you hear the echo of the 10th clap(say).
- Now find the average time for 10 claps. After calculating the time interval "t" between claps and using the formula S=vt, we can calculate the speed of sound.
Question: 46
How we can measure speed of sound by Echo method?
Answer: 46
46-50Measuring speed of sound by Echo method;
Apparatus: measuring tape, stop watch, flat wall that can produce a good echo
Procedure;
- use the tape to measure a distance of 50 meters from the wall.
- Now clap your hands in front of the wall at a distance of 50 meters and check if you can clearly hear an echo from the wall. Make sure the echo is not coming from any other wall in the area. The time taken by the sound to travel 10 meters is the time difference between the clap and the echo.
- Now restart the clapping and start the stop watch at the first clap. Count the number of claps , and stop the clapping and the stop watch when you hear the echo of the 10th clap(say).
- Now find the average time for 10 claps. After calculating the time interval "t" between claps and using the formula S=vt, we can calculate the speed of sound.
Question: 47
Write note on noise pollution?
Answer: 47
47-50Noise ; the sound of irregular frequency and amplitude are known as noise. They produce jarring and unpleasant effect on our ear.
Examples of noise: sound of machinery, the slamming of door and sounds of traffic in big cities.
Musical sound; sound with regular frequency and amplitude are known as musical sound./ They produce pleasant effect on our ears.
Example of music; we enjoy the programmes of radio or television by hearing sounds of different qualities. In musical programmes , we hear sound produced by musical instruments such as flute , harmonium, violin, drum etc. Sound of these instruments has pleasant effect on our ears.
Question: 48
What is acoustic protection? Explain importance of acoustics.
Answer: 48
48-50Acoustic protection: the technique or method used to absorb undesirable sounds by soft and porous surfaces is called acoustic protection.
Reflection of sound is more prominent if the surface is rigid and smooth , and less if the surface is soft and irregular .
Explanation: soft, porous materials, such as draperies and rugs absorb large amount of sound energy and thus quiet echoes and softening noises. Thus by using such material in noisy places we can reduce the level of noise pollution. However, if the surface of classrooms or public halls are too absorbent, the sound level may be low for the audience. Sometimes, when sound reflects from the walls, ceiling , and floor of a room, the reflecting surfaces are too reflective and the sound become garbled. This is due to multiple reflections called reverberations. In the design of lecture halls, auditorium , or theater halls, a balance must be achieved between reverberation and absorption. It is often advantageous to place reflective surfaces behind the stage to direct sound to the audience. Generally , the ceilings of lecture halls , conference halls and theatre halls are curved so that sound after reflection may reach all the corners of the hall. Sometimes curved sound boards are placed behind the stage so that sound after reflection distributed evenly across the hall.
Question: 49
Explain audible frequency range?
Answer: 49
49-50Audible frequency range: the range of frequencies which a human ear can hear is called audible frequency range.
Value of audible frequency range: a normal ear can hear a sound only if its frequency lies between 20 Hz to 20,000 Hz. So human ear neither hears a sound of frequency less than 20 Hz and more than 20,000 Hz. This is called normal hearing frequency range.
Change in audible frequency range; different people have different range of audibility. It decreases with age , For example,
- Young children can hear sounds of 20,000 Hz
- Old people cannot hear sounds even above 15,000 Hz
Question: 50
What are ultrasound ? how they are useful in our practical life?
Answer: 50
50-50Ultrasound: sound of frequency higher than 20,000 Hz which are inaudible to normal human ear are called ultra sound or ultrasonic.
