Wave Optics - Result Question 20

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20. In Young’s experiment, two coherent sources are placed $0.90 mm$ apart and fringe are observed one metre away. If it produces second dark fringe at a distance of $1 mm$ from central fringe, the wavelength of monochromatic light used would be

======= ####20. In Young’s experiment, two coherent sources are placed $0.90 mm$ apart and fringe are observed one metre away. If it produces second dark fringe at a distance of $1 mm$ from central fringe, the wavelength of monochromatic light used would be

3e0f7ab6f6a50373c3f2dbda6ca2533482a77bed:content/english/neet-pyq-chapterwise/physics/wave-optics/wave-optics—result-question-20.md (a) $60 \times 10^{-4} cm$

(b) $10 \times 10^{-4} cm$

(c) $10 \times 10^{-5} cm$

(d) $6 \times 10^{-5} cm$

[1991, 1992]

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Answer:

Correct Answer: 20. (d)

Solution:

  1. (d) For dark fringe

$ \begin{aligned} & x=(2 n-1) \frac{\lambda D}{2 d} \\ & \therefore \lambda=\frac{2 x d}{(2 n-1) D}=\frac{2 \times 10^{-3} \times 0.9 \times 10^{-3}}{(2 \times 2-1) \times 1} \end{aligned} $

$\lambda=0.6 \times 10^{-6} m=6 \times 10^{-5} cm$