The figure represents two identical slits in a Young’s double slit experiment. The width of each slit is b and distance between the centres of the two slits is d. Consider a point P on the screen that is close to centre of the screen. `Delta x_(t)` represents the optical path difference to point P from the top edges of the two slits and `Delta x_(b)` represents the optical path difference to P from the bottom edges of the two slits. Find` Delta x_(b) – Delta x_(t)`.

It is given that `D gtgt d.`

Answer

`(db)/(D)`