• # question_answer The figure shows a Young's double slit experimental setup. It is observed that when a thin transparent sheet of thickness t and refractive index μ is put in front of one of the slits, the central maximum gest shifted by a distance equal to n fringe widths. If the wavelength of light used is $\lambda ,t$will be : [JEE Main 9-4-2019 Morning] A) $\frac{2D\lambda }{a(\mu -1)}$                  B) $\frac{D\lambda }{a(\mu -1)}$C) $\frac{2nD\lambda }{a(\mu -1)}$                D) $\frac{nD\lambda }{a(\mu -1)}$

Path difference at central maxima $\Delta x=(\mu 1)t,$ whole pattern will shift by same amount which will be given by $(\mu 1)t\frac{D}{d}=n\frac{\lambda D}{d},$according to the question $t=\frac{n\lambda }{(\mu -1)}$ no option is matching, therefore question should be awarded bonus. $\therefore$ Correct Option should be (Bonus)