question_answer

In a Young's double slit experiment the source S and the two slits A and B are vertical with slit A above slit B. The fringes are observed on a vertical screen K. The optical path length from S to B is increased very slightly (by introducing a transparent material of higher refractive index) and the optical path length from S to A is not changed, as a result the fringe system on K moves                                                        [NCERT 1984]

A)            Vertically downwards slightly

B)            Vertically upwards slightly

C)            Horizontally, slightly to the left

D)            Horizontally, slightly to the right