A point source emits sound equally in all directions in a non-absorbing medium. Two points P and Q are at distance of 2 m and 3 m respectively from the source. The ratio of the intensities of the waves at P and Q is ......

Options

A. `3:2`
B. `2:3`
C. `9:4`
D. `4:9`

Answer

C

Explanation

We have, `I = (P)/(A) = (P)/( A pi r ^(2)) implies I prop (1)/(r ^(2))`
`therefore (I _(1))/( I _(2)) = (r _(2) ^(2))/( r _(1) ^(2)) = ((3) ^(2))/( (2) ^(2)) = 9/4`
`therefore I _(1) :I _(2) =9:4`