# Intensity of sound

1. Nov 18, 2006

### needhelp83

What is the intensity of sound at the pain level of 120 dB? Compare this to that of a whisper at 20 dB?

I know this should be so simple, but it has me confused.

I have the formula but I am just not sure how to apply it.

I(db)=10 log _ 10 (I/I _ 0)

2. Nov 18, 2006

### physics girl phd

I would probably just assume that the base level (I_0) is 1... then solve each sound level in dB for the sound level in a linear intensity scale... then compare the two sound levels by saying something like... the loud noise is x times louder than the whisper.

3. Nov 18, 2006

### DaveC426913

Wiki has some fascinating information about decibels.

1 bel is a 10-fold increase in sound level. It is dimensionless (like percent, it is only for comparison). 1 decibel is 1/10th of a bel*.

*(So, 1 decibel is a 1-fold increase in sound? i.e. no increase at all? )

4. Nov 19, 2006

### needhelp83

120 dB=10 log (I/1) vs. 20 dB=10 log (I/ 1)

5. Nov 19, 2006

### needhelp83

b=10 log (I/ I0)
120 dB=10 log (I/1)
10^12=(I/ 1)
I= 10^12 W/m^2

b=10 log (I/I0)
20 dB=10 log (I/1)
10^2=(I/1)
I=10^2 W/m^2

The intensity of 120 dB would be 10^12 W/m^2 compared to the whisper with the intensity at 10^2 W/m^2 which equals 10^10 more intense.

Sound good?