Question

A monochromatic beam of light falls on Young's double slit experiment apparatus as shown in figure. A thin sheet of glass is inserted .in front of lower slit $S_2$.
The central bright fringe can be obtained :

• A. At $O$
• B. Above $O$
• C. Below $O$
• D. Anywhere depending on angle $\theta$, thickness of plate $t$, and refractive index of glass $\mu$

Answer 1

The correct option is D Anywhere depending on angle $\theta$, thickness of plate $t$, and refractive index of glass $\mu$

Because of beam inclination means light reaches $S_1$ before it reaches $S_2$, hence an induced time lag before the slits.It means that, without any glass sheet, the central fringe would be above point O because of this inclination

But due to presence of glass sheet, it can be anywhere depending on angle θ, thickness of plate t, and refractive index of glass μ