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JEE Main 2021 (26 Feb, Shift 2) · Beats

Beats question from JEE Main 2021 (26 Feb, Shift 2)

Q49JEE Main 2021 · 26 FEB · SHIFT 2Easy

Beats

A tuning fork A of unknown frequency produces 5 beats/s with a fork of known frequency 340 Hz. When fork A is filed, the beat frequency decreases to 2 beats/s. What is the frequency of fork A?

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Answer: (a)

  1. 5 beats with 340 Hz, so nA=335n_A = 335 or 345 Hz345\text{ Hz}.
  2. Filing raises the frequency of AA, and the beats fall to 2.
  3. Beats fall only if nA<340n_A < 340: 335→338 Hz335 \to 338\text{ Hz} gives 2 beats.
  4. So the answer is (a) 335 Hz.
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