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14. waves and sound — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics14. waves and sound1 Mark
MCQ
When a tuning fork of frequency $341$ is sounded with another tuning fork, six beats per second are heard. When the second tuning fork is loaded with wax and sounded with the first tuning fork, the number of beats is two per second. The natural frequency of the second tuning fork is
  • A
    $334$
  • B
    $339$
  • C
    $343$
  • ✓
    $347$
✓

Answer

Correct option: D.
$347$
d
(d) $n_A =$ Known frequency $= 341\, Hz,$ $n_B = ? $

$x = 6\, bps,$ which is decreasing (i.e. $x\downarrow$) 

after loading (from $6$ to $1\, bps$) 

Unknown tuning fork is loaded so $n_B\downarrow$ 

Hence $n_A -n_B\downarrow = x\downarrow$ ... $(i)$ $\rightarrow$ Wrong 

$n_B\downarrow -n_A = x\downarrow$ ... $(ii)$ $\rightarrow$ Correct 

$\Rightarrow$$n_B = n_A + x = 341 + 6 = 347 Hz.$

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