Question

A tuning fork of frequency 340 Hz is vibrated just above a cylindrical tube of length 120 cm. Water is slowly poured in the tube. If the speed of sound in air is 340 m/s, then the minimum height of water required for resonance is

• A. 25 cm
• B. 45 cm
• C. 75 cm
• D. 95 cm

Answer 1

The correct option is B 45 cm

Wavelength $\lambda =\frac{V}{f}=\frac{340}{340}=1m$

Resonance occurs when height from top is $\frac{\lambda }{4}$ and $\frac{3\lambda }{4},\frac{5\lambda }{4},etc$

At $75cm$, it stops.

$\therefore$ Minimum height is $120-75=45cm$