A double slit `S_1-S_2` is illuminated by a coherent light of wavelength `lamda`. The slits are separated by a distance d. A plane mirror is placed in front of the double slit at a distance `D_1`, from it and a screen `sum` is placed behind the double slit at a distance `D_2`, from it . The screen `sum` receives only the light reflected by the mirror. Find the fringe-width of the interference pattern on the screen.

Answer

A, B, D

Explanation

The apparent distance of the screen from the slits is
`D=2D_1+D_2`
`So fringe width= (Dlamda)/d=((2D_1+D_2)lamda)/d`