• # question_answer             In the Young's double slit experiment, separation between the two slits is 0.9 mm and the fringes are observed one meter away. If it produces the second dark fringe at a distance of 1 mm from the central fringe, then wavelength of the monochromatic source of light used is: A) 400 nm          B) 450 nm           C)      500 nm          D)      600 nm

Correct Answer: D

Solution :

Distance between second dark fringe and central fringe ${{x}_{2}}=\frac{(2n-1)D\lambda }{2d}$ $\therefore$$\lambda =\frac{2d{{x}_{2}}}{(2n-1)d}=\frac{2(0.9\times {{10}^{-3}})\times {{10}^{-3}}}{(2\times 2-1)\times 1}=6\times {{10}^{-7}}\,m$ $=600\,nm.$ Hence, the correction option is (d).

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