Question

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

• A. 9 : 4
• B. 2 : 9
• C. 9 : 2
• D. 4 : 9

Answer 1

The Correct Option is A

Intensity I=\(\frac{p}{\pi r^2}\)

Also 1 \(\propto\) \(\frac{1}{r^2}\)=\(\frac{I_1}{I_2}\)=\(\bigg(\frac{r_2}{r_1}\bigg)^2\)

we have r₁=2m, r₂= 3m 
substituting w have \(\frac{I_1}{I_2}\)=\(\bigg(\frac{3}{2}\bigg)^2\)=\(\frac{9}{4}\)
i.e, 9:4

Therefore, the correct option is (A): 9 : 4