? asked in Science & MathematicsPhysics · 9 years ago

# A quiet library has a sound intensity level of 40 dB, and a riveting machine has a sound intensity level of 12?

A quiet library has a sound intensity level of 40 dB, and a riveting machine has a sound intensity level of 120 dB. How many times greater is the sound intensity of the machine than that of the library

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• ebs
Lv 7
9 years ago

Reference sound intensity Io = 10^−12 W/m² (Threshold of hearing)

Reference sound intensity level LIo = 0 dB-SIL (Threshold of hearing level)

Get sound intensity I1 when entering sound intensity level LI1 = 40 dB:

Sound intesity I1 = Io×10^(LI1/10) W/m² = 10^−12×10^(40/10) = 0.00000001 W/m².

Get sound intensity I2 when entering sound intensity level LI2 = 120 dB:

Sound intesity I2 = Io×10^(LI2/10) W/m² = 10^−12×10^(120/10) = 1 W/m².

Ratio = 1 / 0.00000001 = 100000000 = 10^8.

The sound intensity of the machine is 10^8 times louder than that of the library.

Cheers ebs

• 9 years ago

That will be about 80dB in difference which is in the case of 20 log ( factor ) = 80 means that log ( factor ) must be 4 so its 10.000 times greater.