Question

A thin film $(\mu =1.6)$ of thickness ${10}^{-3}$ mm is introduced in the path of the one of the two interfering beams. The central fringe moves to a position occupied by the ${10}^{th}$ bright fringe earlier. The wavelength of light is:

• A. $600\dot{A}$
• B. $6000\dot{A}$
• C. $60\dot{A}$
• D. $660\dot{A}$

Answer 1

The correct option is A $600\dot{A}$

Shift = $\frac{D}{d}(\mu -1)t$
$\frac{10D\lambda }{d}=\frac{D}{d}(\mu -1)t$
$\lambda =\frac{(1.6-1)\times {10}^{-6}}{10}=6\times {10}^{-8}m=600\dot{A}$