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

Gujarat BoardEnglish MediumSTD 11 SciencePhysics14. waves and sound1 Mark
MCQ
If two tuning forks $A$ and $B$ are sounded together, they produce $4$ beats per second. $A$ is then slightly loaded with wax, they produce $2$ beats when sounded again. The frequency of $A$ is $256.$ The frequency of $B$ will be
  • A
    $250$
  • ✓
    $252$
  • C
    $260$
  • D
    $262$
✓

Answer

Correct option: B.
$252$
b
(b) $n_A $= Known frequency $= 256 Hz,$ $n_B = ?$

$x = 4\, bps$, which is decreasing after loading (i.e. $x\downarrow$) 

also known tuning fork is loaded so $n_A\downarrow$ 

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

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

==>$ n_B = n_A -x = 256 -4 = 252 Hz.$

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