Question

The minimum size of a room required to hear an echo of sound with a speed of $300m/s$ is :

• A. $16$ $m$
• B. $15$ $m$
• C. $14$ $m$
• D. $17$ $m$

Answer 1

The correct option is B $15$ $m$

To hear a distinct echo the time interval between the original sound and the reflected one must be at least $0.15$
As, $V=f\lambda =\frac{1}{T}2x$
$\therefore x=\frac{V\times T}{2}=\frac{300\times 0.1}{2}=15m$