Question

In the ideal double-slit experiment, when a glass-plate (refractive index 1.5) of thickness t is introduced in the path of one of the interfering beams (wavelength `lambda`), the intensity at the position where the central maximum occurred previously remains unchanged. The minimum thickness of the glass-plate is
A. `2lambda`
B. `2lambda//3`
C. `lambda//3`
D. `lambda`

Answer 1

Correct Answer - A
`phi=(2pi)/lambdaDeltax=(2pi)/lambda(mu-1)t`
`phi=0, 2pi, 4pi, …`
`2pi=(2pi)/lambda(1.5-1)t implies t=2lambda`