Optics Ques 144
- A narrow slit of width $1$ $ mm$ is illuminated by monochromatic light of wavelength $600$ $ nm$. The distance between the first minima on either side of a screen at a distance of $2$ $ m$ is
(1994, 1M)
(a) $1.2 $ $cm$
(b) $1.2$ $ mm$
(c) $2.4 $ $cm$
(d) $2.4$ $ mm$
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Answer:
Correct Answer: 144.(d)
Solution:
Formula:
- For first dark fringe on either side $d \sin \theta=\lambda$
$ \text { or } \quad \frac{d y}{D} =\lambda $
$\therefore \quad y =\frac{\lambda D}{d}$
Therefore, distance between two dark fringes on either side
$ =2 y=\frac{2 \lambda D}{d} $
Substituting the values, we have
$ \text { Distance }=\frac{2\left(600 \times 10^{-6} mm\right)\left(2 \times 10^{3} mm\right)}{(1.0 mm)}=2.4$ $ mm $
BETA
