Question

The central fringe of interference pattern produced by light of wavelength $6000\mathring{A}$ is found to shift to the position of $4^{th}$ bright fringe, after a glass plate of $\mu =1.5$ is introduced. The thickness of the glass plate is :

• A. $4.8\mu m$
• B. $8.23\mu m$
• C. $14.98\mu m$
• D. $3.78\mu m$

Answer 1

The correct option is A $4.8\mu m$

We know,

shift at $n^{th}$ bright fringe is

$(\mu -1)t=n\lambda$

Given $\mu =1.5$

$n=4$

$\lambda =6000\stackrel{o}{A}$

So $(1.5-1)t=4(6000\times {10}^{-10})$

$t=4.8\times {10}^{-6}m$

$\Rightarrow t=4.8\mu m$

So $\left(A\right)$ is correct