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JEE Main 2021 (26 Aug, Shift 1) · YDSE: Fringe Width & Fringe Positions

YDSE: Fringe Width & Fringe Positions question from JEE Main 2021 (26 Aug, Shift 1)

Q59JEE Main 2021 · 26 AUG · SHIFT 1Medium

YDSE: Fringe Width & Fringe Positions

White light is passed through a double slit and interference is observed on a screen 1.5 m away. The separation between the slits is 0.3 mm. The first violet and red fringes are formed 2.0 mm and 3.5 mm away from the central white fringes. the difference in wavelengths of red and violet light is ................ nm.

Numerical answer type. Work it out, then open the answer.

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Answer: 300

  1. First bright fringe: y1=λDdy_1 = \frac{\lambda D}{d}, so Δλ=Δy dD\Delta\lambda = \frac{\Delta y\, d}{D}.
  2. Δλ=(3.5−2.0)×10−3×0.3×10−31.5=3×10−7\Delta\lambda = \frac{(3.5-2.0)\times10^{-3}\times0.3\times10^{-3}}{1.5} = 3\times10^{-7} m
  3. So the answer is 300 nm.
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