Verified Solution • 2025–26 Session moderate

QJEEM20Ph193b: JEE Main 2020 Physics - Class 12 JEEM20Ph193b Solution: In a Young’s double slit experiment, 16 fringes are observed in …

In a Young’s double slit experiment, 16 fringes are observed in a certain segment of the screen when light of a wavelength 700 nm is used. If the wavelength of light is changed to 400 nm, the number of fringes observed in the same segment of the screen would be

Multiple Choice Options

  • A 28
  • B 24
  • C 30
  • D 18

Step-by-Step Verified Solution

Let the length of segment is "l"

Let N is the no. of fringes in "l" and w is fringe width.

∴ Nw = l

⇒ N(λDd) = l

As in both cases segment length is same.

∴ N1λ1Dd=l

and N2λ2Dd=l

∴ N1λ1Dd = N2λ2Dd

⇒ N1λ1 = N2λ2

⇒ 16 × 700 = N2 × 400

⇒ N2 = 28

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