question_answer

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 \[(wave-lenght\lambda )\], the intensity at the position where the central maximum occurred previously remains unchanged. The minimum thickness of the glass-plate is

A) \[2\lambda \] 

B) \[2\lambda /3\]

C) \[\lambda /3\]

D) \[\lambda \]