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 wave function, Ψn,l,ml is a mathematical function whose value depends upon spherical polar coordinates (r, θ, Ф) of the electron and characterized by the quantum numbers n, l and m. Here r is distance from nucleus, θ is colatitude and Ф is azimuth. In the mathematical functions given in the Table, Z is atomic number and a0 is Bohr radius.

Column 1 Column 2 Column 3
(i) 1s orbital (i) Ψn,l,ml(Za0)32e(Zra0) (P)
(ii) 2s orbital (ii) One radial node (Q) Probability density at nucleus 1a30
(iii) 2 pz orbital (iii) Ψn,l,ml(Za0)52re(Zr2a0)cosθ (R) Probability density is maximum at nucleus
(iv) 3d2z orbital (iv) xy-plane is a nodal plane (S) Energy needed to excite electron from n = 2 state to n = 4 state is2732 times the energy needed to excite electron from n = 2 state to n = 6 state

For the given orbital in Column 1, the only CORRECT combination for any hydrogen-like species is