PhysicsNEET 2025Superposition, standing waves, beats

Waves

A pipe open at both ends has a fundamental frequency $f$ in air. The pipe is now dipped vertically in a water drum to half of its length. The fundamental frequency of the air column is now equal to:

A. $\frac{f}{2}$
B. $f$ ✓
C. $\frac{3 f}{2}$
D. $2 f$

Solution

Open pipe of length $L$ : $f = \frac{v}{2 L}$ . Dipped to half its length it becomes a closed pipe of length $\frac{L}{2}$ : $f^{'} = \frac{v}{4 ( L /2 )} = \frac{v}{2 L} = f$ .

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