Question

In YDSE, when a glass plate of refractive index $1.5$ and thickness $t$ is placed in the path of one of the interfereing beams (wavelength $\lambda$), intensity at the position where central maximum occurred previously unchanged. The minimum thickness of the glass plate is

• A. $2\lambda$
• B. $\left(2/3\right)\lambda$
• C. $\lambda /3$
• D. $\lambda$

Answer 1

The correct option is A $2\lambda$

For minimum thickness, $(n-1)t=\lambda$

$t=\frac{\lambda }{(n-1)}=\frac{\lambda }{(1.5-1)}=2\lambda$