# 17.3 Sound intensity  (Page 4/14)

 Page 4 / 14

## Changing intensity levels of a sound

Show that if one sound is twice as intense as another, it has a sound level about 3 dB higher.

## Strategy

We are given that the ratio of two intensities is 2 to 1, and are then asked to find the difference in their sound levels in decibels. We can solve this problem by using of the properties of logarithms.

## Solution

1. Identify knowns:
The ratio of the two intensities is 2 to 1, or
$\frac{{I}_{2}}{{I}_{1}}=2.00.$

We wish to show that the difference in sound levels is about 3 dB. That is, we want to show:
${\beta }_{2}-{\beta }_{1}=3\phantom{\rule{0.2em}{0ex}}\text{dB.}$

Note that
${\text{log}}_{10}b-{\text{log}}_{10}a={\text{log}}_{10}\left(\frac{b}{a}\right).$
2. Use the definition of $\beta$ to obtain
${\beta }_{2}-{\beta }_{1}=10\phantom{\rule{0.2em}{0ex}}{\text{log}}_{10}\left(\frac{{I}_{2}}{{I}_{1}}\right)=10\phantom{\rule{0.2em}{0ex}}{\text{log}}_{10}2.00=10\left(0.301\right)\phantom{\rule{0.2em}{0ex}}\text{dB}\text{.}$

Thus,
${\beta }_{2}-{\beta }_{1}=3.01\phantom{\rule{0.2em}{0ex}}\text{dB}\text{.}$

## Significance

This means that the two sound intensity levels differ by 3.01 dB, or about 3 dB, as advertised. Note that because only the ratio ${I}_{2}\text{/}{I}_{1}$ is given (and not the actual intensities), this result is true for any intensities that differ by a factor of two. For example, a 56.0-dB sound is twice as intense as a 53.0-dB sound, a 97.0-dB sound is half as intense as a 100-dB sound, and so on.

Check Your Understanding Identify common sounds at the levels of 10 dB, 50 dB, and 100 dB.

10 dB: rustle of leaves; 50 dB: average office; 100 dB: noisy factory

Another decibel scale is also in use, called the sound pressure level    , based on the ratio of the pressure amplitude to a reference pressure. This scale is used particularly in applications where sound travels in water. It is beyond the scope of this text to treat this scale because it is not commonly used for sounds in air, but it is important to note that very different decibel levels may be encountered when sound pressure levels are quoted.

## Hearing and pitch

The human ear has a tremendous range and sensitivity. It can give us a wealth of simple information—such as pitch, loudness, and direction.

The perception of frequency is called pitch    . Typically, humans have excellent relative pitch and can discriminate between two sounds if their frequencies differ by 0.3% or more. For example, 500.0 and 501.5 Hz are noticeably different. Musical notes    are sounds of a particular frequency that can be produced by most instruments and in Western music have particular names, such as A-sharp, C, or E-flat.

The perception of intensity is called loudness    . At a given frequency, it is possible to discern differences of about 1 dB, and a change of 3 dB is easily noticed. But loudness is not related to intensity alone. Frequency has a major effect on how loud a sound seems. Sounds near the high- and low-frequency extremes of the hearing range seem even less loud, because the ear is less sensitive at those frequencies. When a violin plays middle C, there is no mistaking it for a piano playing the same note. The reason is that each instrument produces a distinctive set of frequencies and intensities. We call our perception of these combinations of frequencies and intensities tone quality or, more commonly, the timbre    of the sound. Timbre is the shape of the wave that arises from the many reflections, resonances, and superposition in an instrument.

who discover periodic table?
it wasn't discovered , it was made.and the person who made it was dmitri mendeleev. dobreinier and newland gave their laws before dmitri related periodic table but wasn't successful in their work
Ritik
Nope, numerous number of scientist had actually contributed in the making of periodic table. Dmitri Mendeleev succeeded making all the elements into the right order in accordance to their atomic number.
Dame
what is the Greek name for calcium
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longitudinal and transverse waves
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a gun is kept in the state that it cannot move anywhere and the bullet is fired. Then what is the effect on the velocity of bullet and KE of gun ?
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it refers to the sun and all heavenly bodies revolving around it.
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excatly...for sure
Arzoodan
in addition to Danie's, a solar system is a collection of planets and their moons, asteroids, and other objects bound together by the Star's gravitational force directly or indirectly.
Galiwango
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what iw meant by total internal reflection
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Lorentz force?
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study fibre optics. .you will get total internal reflection
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jyotirmayee
what is Lorentz force?
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a ray of light traveling at an angle of incidence greater than critical angle from denser to rarer medium is totally reflected back into the denser medium is called total internal reflaction
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motion in strat line where is this chapter
motion in straight line is kinematic's part
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yea
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this defination isn't correct
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what is maxwell electromagnetic law?
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a dynamo converts mechanical energy to electrical while a pump is opposite to that
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why sea water looks bluish?
cuz the sky is blue...
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you see the reflexion of the "blue" sky in the water
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somewhere sea water turns green why?
Piyali
never seen bro... are u sure ?
Mehdi
ur answer was correct but due to the presence of phytoplankton color can be changed near the shore
Piyali
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because of the reflection of the sky
Friday
rays coming from the sun consist of all 7 colours ie.VIBGYOR. when the ray strikes surface of water,all colors gets absorbed by it except blue which gets reflected by it.so we find the sea water appearing bluish
Ritik
how can someone identify sea water from rain water
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i think it's not possible as because rainwater consists of water from all kind of water bodies ie.lakes,seas etc but u can predict if u have a sea nearby ur home or city
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The difference is said in the word itself. There is no existance of reaction without an application of action. So action occur first then reaction. Reaction may produce in body itself or to other body i.e., it may be internal or external.
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or we can say , reaction is the result of action
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