Q.
A sound wave of wavelength $32\ cm$ enters the tube at $S$ as shown in the figure. Then the smallest radius $r$ so that a minimum of sound is heard at detector $D$ is
A) $7\ cm$
B) $14\ cm$
C) $21\ cm$
D) $28\ cm$
Explanation
(b) Path difference $(\pi r - 2r) = \frac{\lambda}{2} = \frac{32}{2} = 16$
$r = \frac{16}{\pi - 2} = 14cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.