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Wave Optics — JEE physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 ScienceJEE physicsWave Optics1 Mark
MCQ
light is incident normally on a diffraction grating through which the first order diffraction is seen at $32.$ The second order diffraction will be seen at
  • A
    $ 48$
  • B
    $ 64$
  • C
    $80$
  • ✓
    There is no second order diffraction in this case
✓

Answer

Correct option: D.
There is no second order diffraction in this case
For a grating, $(e+d) \sin \theta_n=n \lambda$
where $(e+d)=$ greating element
$\sin \theta_n=\frac{n \lambda}{(e+d)}$
For $n=1, \sin \theta_1=\frac{\lambda}{(e+d)}=\sin 32^{\circ}$
This is more than 0.5 . Now $\sin \theta_2$ will be more than $2 \times 0.5$, which is not possible.

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