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JEE PHYSICS MCQ: WAVE OPTICS

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In a double slit experiment, two parallel slits are illuminated first by light of wavelength

400 \mathrm{~nm}

and then by light of unknown wavelength. The fourth order dark fringe resulting from the known wavelength of light falls in the same place on the screen as the second order bright fringe from the unknown wavelength. The value of unknown wavelength of the light is

View answer and explanation

Correct option: B

700 \mathrm{~nm}

Option B (

700 \mathrm{~nm}

) is correct because the condition for dark fringes in a double-slit experiment is

(n + \frac{1}{2})\frac{{D\lambda_1}}{{d}} = m \frac{{D\lambda_2}}{{d}}

, where

n

and

m

are integers.

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