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NEET 2019 · Diffraction at a Single Slit

Diffraction at a Single Slit question from NEET 2019

Q68NEET 2019Easy

Diffraction at a Single Slit

Angular width of the central maxima in the Fraunhofer diffraction for $\lambda = 6000$ Å 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

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Answer: (c)

Angular width of central maximum $= \dfrac{2\lambda}{a} \propto \lambda$ for the same slit.
A $30\%$ decrease means $\lambda' = 0.7 \times 6000\text{ \AA} = 4200\text{ \AA}$ .
So the answer is (c) $4200\text{ \AA}$ .

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