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  4. Angular width of the central maxima in the Fraunhofer diffraction for λ = 6000 mathringA is θ0. When the same slit is illuminated by another monochromatic light, the angular width decreases by 30%. The wavelength of this light is,

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

NEETNEET 2019Wave Optics

Solution:

Angular width $\propto \frac{\lambda}{d}$
$\Rightarrow \frac{\theta_{0}}{0.7\theta_{0}} = \frac{\frac{6000\,\mathring{A}}{d}}{\frac{\lambda}{d}} $
$ \Rightarrow \lambda = 4200 \,\mathring{A}$