the sound intensity level at a point 4m from the point source is 10dB, then the sound level at a distance 2m from the same source will be ?
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Imagine that sound travels in a spherical wavefront.
The first point we consider is on the surface of a sphere of radius 4m and the second point is on a sphere of radius 2m.
Intensity is Power per unit area.
Now power is the same everywhere in this case.
So intensity is inversely proportional to the area. (of the sphere).
In the first case the area is 4π(4)^2 = 64π m^2
In the 2nd case, the area is 4π(2)^2 = 16π m^2
So we can see that Area became a quarter of what it was before. Now since Intensity is inversely proportional to the area, the intensity now must be 4 times of what it was initially.
=10×4
= 40 dB
The first point we consider is on the surface of a sphere of radius 4m and the second point is on a sphere of radius 2m.
Intensity is Power per unit area.
Now power is the same everywhere in this case.
So intensity is inversely proportional to the area. (of the sphere).
In the first case the area is 4π(4)^2 = 64π m^2
In the 2nd case, the area is 4π(2)^2 = 16π m^2
So we can see that Area became a quarter of what it was before. Now since Intensity is inversely proportional to the area, the intensity now must be 4 times of what it was initially.
=10×4
= 40 dB
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