Question

A tuning fork of frequency 340 Hz is sounded above an organ pipe of length 120 cm. Water is now slowly poured in it. The minimum height of water column required for resonance is (speed of sound in air = 340 m/s)

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

Answer 1

The correct option is B 95 cm

When water is poured the wavelength of standing wave in water column decreases and frequency increases.

The frequency will be $f=\frac{c}{\lambda }$, where c is velocity of sound and $\lambda$ is wavelength of interfering wave

$\frac{\lambda }{4}=L\Rightarrow \lambda =4L$ where $L$ is length of air column

$\frac{c}{4L}=340Hz$

given $c=340$ m/s

$L=25cm$

water to be poured upto $120-25=95$ cm