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

Gujarat BoardEnglish MediumSTD 11 SciencePhysics14. waves and sound1 Mark
MCQ
On sounding tuning fork $A$ with another tuning fork $B$ of frequency $384 Hz, 6$ beats are produced per second. After loading the prongs of $A$ with some wax and then sounding it again with $B, 4$ beats are produced per second. What is the frequency of the tuning fork $A$  .... $Hz$
  • A
    $388$
  • B
    $380$
  • C
    $378$
  • ✓
    $390$
✓

Answer

Correct option: D.
$390$
d
(d) $n_A = ?, n_B = 384 Hz$
$x = 6\, bps$, which is decreasing (from $6$ to $4$) i.e. $x\downarrow$
Tuning fork $A$ 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_A = n_B + x = 384 + 6 = 390 Hz.$

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