Question

A double slit $S_1-S_2$ is illuminated by a coherent ight of wavelength \lambda 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 (figure 17 - E2). The screen $\sum$ receives only the light reflected by the mirror. Find the fringe -width fo te interference pattern on the screen.

Answer 1

The apparent distance of the screen from the slits is ,
$D=2D_1+D_2$
So, Fringe width$=\frac{D\lambda }{d}=\frac{(2D_1+D_2)\lambda }{d}$