Question

If the distance between the source of sound and observer is reduced to one half, then

the intensity of sound will become

Answer 1

Let the power delivered by the sound wave be 'P'

Intensity by definition is the power delivered per unit area.

i.e. I =

dA

dP

;

In spherical polar coordinate system dA = r

2

Ω

I =

r

2

Ω

dP

;

I ∝

r

2

1

So if distance increases 3 fold. The Intensity becomes

9

1

times the initial