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

Gujarat BoardEnglish MediumSTD 11 SciencePhysics14. waves and sound1 Mark
MCQ
A tuning fork of frequency $100$ when sounded together with another tuning fork of unknown frequency produces $2$ beats per second. On loading the tuning fork whose frequency is not known and sounded together with a tuning fork of frequency $100$ produces one beat, then the frequency of the other tuning fork is
  • ✓
    $102$
  • B
    $98$
  • C
    $99$
  • D
    $101$
✓

Answer

Correct option: A.
$102$
a
(a) Suppose $ n_A$ = known frequency $= 100 \,Hz, \,n_B\, = ?$

$x = 2 =$ Beat frequency, which is decreasing after loading (i.e.$x\downarrow$)

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

==> $n_B = n_A + x = 100 + 2 = 102 Hz.$

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