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JEE Main 2017 · YDSE: Film, Medium & Two Wavelengths

YDSE: Film, Medium & Two Wavelengths question from JEE Main 2017

Q64JEE Main 2017Medium

YDSE: Film, Medium & Two Wavelengths

In a Young’s double slit experiment, slits are separated by 0.5 mm, and the screen is placed 150 cm away. A beam of light consisting of two wavelengths, 650 nm and 520 nm, is used to obtain interference fringes on the screen. The least distance from the common central maximum to the point where the bright fringes due to both the wavelengths coincide is

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Answer: (c)

  1. Coincidence: n1×650=n2×520⇒n1n2=45n_1 \times 650 = n_2 \times 520 \Rightarrow \dfrac{n_1}{n_2} = \dfrac{4}{5}, so n1=4n_1 = 4.
  2. y=4×650×10−9×1.50.5×10−3=7.8×10−3 my = \dfrac{4 \times 650\times10^{-9} \times 1.5}{0.5\times10^{-3}} = 7.8\times10^{-3}\text{ m}
  3. So the answer is (c) 7.8 mm.
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