Question

If the amplitude of a wave at a distance $r$ from a point source is $A$, the amplitude at a distance $2r$ will be

• A. $2A$
• B. $A$
• C. $\frac{A}{2}$
• D. $\frac{A}{4}$

Answer 1

Answer: (C)

$I\propto A^2$
Also, $I\propto \frac{1}{r^2}$ (inverse square law)
$A\propto \frac{1}{r}$
$\therefore A=\frac{A}{2}$