Physics Learning Objective on Sound Intensity

1. Physics 101 Learning Object
Combining and Comparing Intensities of Sound Waves
If a single object produces a sound intensity level, having two items does
not mean the sound intensity doubles.
Eg. If a chainsaw one metre away produces a sound intensity level of 110
dB, what is the sound intensity level of two chainsaws one metre away?
The answer is not: (110 dB) * 2 = 220 dB
Instead, the intensities (I) must be combined in the equation:
Answer:
1. Isolate I from the equation. Given that I0 = 1.00 x 10^-12

2. I =
2. Therefore, in this case, I= (10^11)*(1.00*10^-12) and then we multiply
that by 2 due to the two chainsaws. Therefore, the intensity is found to be
0.2 W/m^2.
3. Substituting back into the sound intensity level formula,
= 10log(0.2/ 1.00x10^-12) = 113.0103 dB
Instead of 220 db which may seem like the obvious answer, we get
approximately 113 db instead. From this, we can see that while doubling
the intensity with two sound sources instead of one, the sound intensity
only raises by about 3 dB. Therefore, an increase of 3 dB is equivalent to
doubling of the sound intensity.