(IIT 1984 - Multi ans correct)
White light is used to illuminate the 2 slits in a Young's double slit experiment.The separation between the slits is b and the screen is at a distance d(>b) from the slits.At a point on the screen directly is front of one of the slits,certain wavelengths are missing.Some of these missing wavelengths are
(A) λ=b2d
(B) λ=2b2d
(C) λ=b2d
(D) λ=2b23d
1At a point infront of slit 1 let it be P
distance from central line bisecting two slits =b2
Therefore path difference, \Delta X=S2P - S1P = ybd= b2.bd=b22d
Those wavelengths will be missing for which
\Delta X = \frac{\lambda _{1}}{2}, \frac{3\lambda _{}}{2},....
Therefore \lambda _{1}}=2\Delta X = b2d
\lambda _{2} = b23d
\lambda _{3} = b25d
SO correct options r (A,C)
