Question

A plane monochromatic light wave falls normally on a diaphragm with two narrow slits separated by $2.5\text{mm}$. The fringe pattern is formed on a screen $100\text{cm}$ behind the diaphragm. By what distance will these fringes be displaced, when one of the slits is covered by a glass plate $(\mu =1.5)$ of thickness $10\mu \text{m}$?

• A. $2\text{mm}$
• B. $1\text{mm}$
• C. $3\text{mm}$
• D. $4\text{mm}$

Answer 1

The correct option is A $2\text{mm}$

Shift caused due to the introduction of glass plate,

$\Delta y=\frac{(\mu -1)tD}{d}$

$=\frac{(1.5-1)(10\times {10}^{-6})\left(1\right)}{2.5\times {10}^{-3}}$

$=2\times {10}^{-3}\text{m}=2\text{mm}$

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