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MHT CET 2020 (19 Oct, Shift 2) · Beats

Beats question from MHT CET 2020 (19 Oct, Shift 2)

Q54MHT CET 2020 · 19 OCT · SHIFT 2Easy

Beats

A tuning fork $A$ produces 5 beats per second with a tuning fork of frequency 480 Hz. When a little wax is stuck to a prong of fork $A$ , the number of beats heard per second becomes 2. What is the frequency of tuning fork $A$ before the wax is stuck to it?

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Answer: (d)

5 beats with 480 Hz, so $n_A = 480 \pm 5 = 485$ or $475\text{ Hz}$ .
Wax lowers the frequency of $A$ , and the beats fall from 5 to 2.
Beats fall only if $n_A$ moves closer to 480, so $n_A > 480$ : $485 \to 482\text{ Hz}$ gives 2 beats.
So the answer is (d) 485 Hz.

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