Angular width of the central maxima the Fraunhofer diffraction fo… - Vidyadip

MCQ

Angular width of the central maxima the Fraunhofer diffraction for $\lambda=6000 \;\mathring A$ is $\theta_{0} .$ When the same slit Is lluminated by another monochromatic light, the angular wildth decreases by $30 \% .$ The wavelength of this light is.......$\mathring A$

A
$1800$
✓
$4200$
C
$6000$
D
$420$

✓

Answer

Correct option: B.

$4200$

b
Angular width $\propto \frac{\lambda}{\mathrm{d}} $

$\Rightarrow \frac{\theta_{0}}{0.7 \theta_{0}}=\frac{\frac{6000 {\mathring A}}{\mathrm{d}}}{\frac{\lambda}{\mathrm{d}}} $$\Rightarrow \lambda=4200 \mathring A$

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