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

Gujarat BoardEnglish MediumSTD 11 SciencePhysics14. waves and sound1 Mark
MCQ
A second harmonic has to be generated in a string of length $l$ stretched between two rigid supports. The points where the string has to be plucked and touched are respectively
  • ✓
    $\frac{l}{4}, \frac{l}{2}$
  • B
    $\frac{l}{4}, \frac{3l}{4}$
  • C
    $\frac{l}{2}, \frac{l}{2}$
  • D
    $\frac{l}{2}, \frac{3l}{4}$
✓

Answer

Correct option: A.
$\frac{l}{4}, \frac{l}{2}$
a
(a)

In the $2^{\text {nd }}$ harmonic the shape of wave looks like.

The point of touching forms a node point of plucking forms an antinode. Hence, for $2^{\text {nd }}$ harmonic, we need to need wire touched at $\frac{l}{2}$ and pluck it at $\frac{l}{4}$.

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