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

Options

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

Answer

a

Explanation

The average power per unit area that is incident perpendicular to the direction of propagation is called intensity, i.e,.
`I=(P)/(4pir^(2))`
or `I prop (1)/(r^(2))implies (I_(1))/(I_(2))=((r_(2))/(r_(1)))^(2)`
Hence, `r_(1)= 2m, r_(2)=3m`
`:. (I_(1))/(I_(2))=((3)/(2))^(2)= (9)/(4)`