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JEE Main 201815 April
Exam
JEE Main
Year
2018
Date
15 April
Subject
Physics
Chapter
Waves and Sound

JEE Main 2018 · 15 April · Physics · Waves and Sound

A tuning fork vibrates with frequency 256Hz and gives one beat per...

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})

Options

  1. A220cm220cm
  2. B200cm200cm
  3. C190cm190cm
  4. D180cm180cm

Correct answer

B. 200cm200cm

Step-by-step solution

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

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