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10. Wave optics — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics10. Wave optics1 Mark
MCQ
In a two slit experiment with monochromatic light fringes are obtained on a screen placed at some distance from the sits. If the screen is moved by $5 \times {10^{ - 2}}m$ towards the slits, the change in fringe width is $3 \times {10^{ - 5}}m$. If separation between the slits is ${10^{ - 3}}m$, the wavelength of light used is.........$\mathop A\limits^o $
  • ✓
    $6000$
  • B
    $5000$
  • C
    $3000 $
  • D
    $4500 $
✓

Answer

Correct option: A.
$6000$
a
(a)$\beta = \frac{{\lambda D}}{d}$ ==> $\beta$ $\propto$ $D$
==> $\frac{{{\beta _1}}}{{{\beta _2}}} = \frac{{{D_1}}}{{{D_2}}}$ ==> $\frac{{{\beta _1} - {\beta _2}}}{{{\beta _2}}} = \frac{{{D_1} - {D_2}}}{{{D_2}}}$==> $\frac{{\Delta \beta }}{{\Delta D}} = \frac{{{\beta _2}}}{{{D_2}}} = \frac{{{\lambda _2}}}{{{d_2}}}$
$ = {\lambda _2} = \frac{{3 \times {{10}^{ - 5}}}}{{5 \times {{10}^{ - 2}}}} \times {10^{ - 3}} = 6 \times {10^{ - 7}}m = 6000{Å}$

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