Q. A glass tube $1.5\ m$ long and open at both ends, is immersed vertically in a water tank completely. A tuning fork of 660 $Hz$ is vibrated and kept at the upper end of the tube and the tube is gradually raised out of water. The total number of resonances heard before the tube comes out of water, taking velocity of sound air $330\ m/sec$ is
A) 12
B) 6
C) 8
D) 4
Explanation
(b) Suppose $N$ resonance occurred before tube coming out
Hence by using $l = \frac{(2N - 1)v}{4n}$
$\Rightarrow 1.5 = \frac{(2N - 1) \times 330}{4 \times 660} \Rightarrow N \approx 6$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.