Waves - Result Question 10
10. A point source emits sound equally in all directions in a non-absorbing medium. Two points $P$ and $Q$ are at distances of $2 m$ and $3 m$ respectively from the source. The ratio of the intensities of the waves at $P$ and $Q$ is[2005]
(a) $3: 2$
(b) $2: 3$
(c) $9: 4$
(d) $4: 9$
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Answer:
Correct Answer: 10. (c)
Solution:
- (c) Intensity $=$ Energy/sec/unit area
Area $\propto r^{2} \Rightarrow I \propto 1 / r^{2}$
$\Rightarrow \frac{I_1}{I_2}=\frac{r_2^{2}}{r_1^{2}}=\frac{3^{2}}{2^{2}}=\frac{9}{4}$
