Waves

JEE Main level, single correct, medium

104 of 142

Question 104 of 142

A tuning fork vibrates with frequency 256Hz256Hz and gives one beat per second with the third normal mode of vibration of an open pipe. What is the length of the pipe? (speed of sound in air is 340ms−1340m{s}^{-1})

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Answer: (B) 200cm200cm

Organ pipe will have frequency either 255255 or 257Hz257Hz. Using 255Hz255Hz,
255=3v2l,⇒l=3×3402×255m255=\dfrac{3v}{2l},\Rightarrow l=\dfrac{3\times 340}{2\times 255}m⇒l=200cm\Rightarrow l=200cm. Using 257Hz257Hz,257=3v2l′⇒l′=3×3402×257m=198cm.257=\dfrac{3v}{2l'}\Rightarrow l'=\dfrac{3\times 340}{2\times 257}m=198cm.

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