Sound Intensity Formula

Sound Intensity Formula

Sound intensity is defined as sound per unit area perpendicular to direction of sound waves represented by I. The SI unit of sound intensity is watt per square meter (W/m2). The standard text is the measurement of sound intensity of the noise in the air at the location of the listener as a sound energy quantity.

The sound intensity formula is given as,


P = sound power,

A = area

To measure Sound intensity level, you need to compare the given sound intensity with the  standard intensity.

Sound Intensity Level Formula is given as,

Where I = sound intensity and

          Io = reference intensity

It is expressed in decibels (dB).

Example 1

A person whistles with the power of 0.9 × 10-4 W. Calculate the sound intensity at a distance of 7m.



Sound power P = 0.9 × 10-4 W,

Area A = 7m

Sound intensity formula is given by I = P / A

                                        = 0.9×104 / 7

                                        = 1.28 x 10-5 W/m2.

Example 2

Determine the intensity level which is equivalent to an intensity 1 nW/m2.


Intensity Level formula is given by

IL = 10 log10 I / I0


I = 1 nWm-2 = 1 × 10-9 Wm-2,

   Io = 10-12 Wm-2

IL= 10 log10 1×109 / 1012

 = 10 log10 103

 = 3.


Practise This Question

The diagram shows a capacitor C and a resistor R connected in series to an ac source. V1 and V2 are voltmeters and A is an ammeter

Consider now the following statements

1) Readings in A and
V2 are always in phase
Reading in V1 is ahead in phase with reading in V2
3) Readings in A and V1 are always in phase which of these statements are / is correct

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