A tuning fork of frequency 480 Hz produces 10 beats per second when sounded with a vibrating sonometer…

A tuning fork of frequency 480 Hz produces 10 beats per second when sounded with a vibrating sonometer string. What must be the frequency of the
  1. 460 Hz
  2. 470 Hz
  3. 480 Hz
  4. 490 Hz

Solution

Frequency of string may be $470\text{ Hz}$ or $490\text{ Hz}$. With increase in tension, frequency of string will increase. If initially, it is $470\text{ Hz}$, beat frequency with given tuning fork will decrease. If it is $490\text{ Hz}$, beat frequency will increase.

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