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Please explain what a negative sound level, such as -10 db, is.Objectives are to...

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castillonunez08 | Student, Undergraduate | eNotes Newbie

Posted August 23, 2011 at 9:37 AM via web

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Please explain what a negative sound level, such as -10 db, is.

Objectives are to (1)demonstrate the properties that sound shares with other waves, (2)relate the physical properties of sound waves to our perception of sound, and (3)identify some applications of the Doppler effect.

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lambertd | High School Teacher | eNoter

Posted August 23, 2011 at 1:21 PM (Answer #1)

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1. Sound works like an ocean wave it could even be refered to as a mechanical wave. Imagine bouncing a slinky in an up and down fashion.

2. As you move toward the sound you collide with even more sound waves which increases the intensity of the sound(waves become shorter), it gets loud. As you move away from sound it becomes softer due to the fact that, waves become longer.

3. The doppler effect can be used for things such as topographic mapping. The quicker the waves return the "louder" the sound. The doppler effect is used by mammals such as bats which is known as echo location. The sound that returns quicker lets the oranism know the distance of the object. Last and final the doppler effect of light is used daily in the field of astronomy as proposed by Edwin Hubble. Hubble discovered that as stars move away their wavelength becomes longer and turns red and as light travels toward us it becomes shorter and appears blue.

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valentin68 | College Teacher | (Level 3) Associate Educator

Posted October 27, 2013 at 8:06 AM (Answer #2)

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The decibel is by definition a dimensionless logarithmic quantity from a the intensity of sound reported to a standard reference intensity.

`dB =10*log(I/I_0)` 

where `I_0 =10^-12 W/m^2`

The reference intensity is taken as the lowest sound intensity that in normal conditions is audible. Lower sound intensity levels than the reference intensity are usually inaudible.

The corresponding sound intensity for a -10 dB level is

`-10 =10*log(I/I_0)`

`-1 =log(I/I_0)`

`I =I_0*10^-1 =10^-12*10^-1 =10^-13 W/m^2`

Sound is just an oscillation of the air molecules and thus it is transmitted over large distances like a wave. The decibel scale was invented as a necessity to measure oscillations intensities spread over a very wide range (for example the highest audio sound intensity when all the air in one semi-plane of the oscillation is depleted, is about `10^20`  ` ` times the lowest audible sound). The human perception of sound (the ear) is working in a range of intensities of about `10^14` .

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