Question

Interference pattern is produced in a Young's double slit experiment and a thin piece of plane parallel glass slab $(\mu =1.5)$ is placed in front of one of the slits. If the fringes are displaced through a distance equal the fringe width, find the thickness of the glass slab. Take wavelength of light $\lambda =6000\mathring{\text{A}}$.

• A. $1.2\mu \text{m}$
• B. $0.6\mu \text{m}$
• C. $1.8\mu \text{m}$
• D. $3.6\mu \text{m}$

Answer 1

The correct option is A $1.2\mu \text{m}$

When a thin glass plate is placed in front of one of the slits, the pattern shifts through a distance $\Delta y$, given by,

$\Delta y=\frac{\beta }{\lambda }(\mu -1)t$

$\Rightarrow t=\frac{\Delta y\lambda }{\beta (\mu -1)}$

Here, $\Delta y=\beta$
$\Rightarrow t=\frac{\lambda }{(\mu -1)}$
$=\frac{6\times {10}^{-7}}{(1.5-1)}=1.2\mu \text{m}$

Hence, $\left(A\right)$ is the correct answer.