Q 11-14-140JEE MainJEE Main 2025 (3 Apr, Shift 2)Easy
In the resonance experiment, two air columns (closed at one end) of $100\ \text{cm}$ and $120\ \text{cm}$ length give $15$ beats per second when each one is sounding in its respective fundamental mode. The velocity of sound in the air column is:
Answer: (D) $360\ \text{m/s}$
The fundamental of a closed pipe is $f = \dfrac{v}{4l}$ (end correction ignored).
$$f_1 - f_2 = \frac v4\left(\frac1{1.0} - \frac1{1.2}\right) = \frac v4\cdot\frac16 = \frac{v}{24} = 15$$
$$v = 360\ \text{m/s}$$
Solution by Sreeraj P, M.Sc Physics