Question

In YDSE, find the thickness of a glass slab $(\mu =1.5)$ which should be placed before the upper slit $S_1$ so that the central maximum now lies at a point where $5^{th}$ bright fringe was laying earlier (before inserting the slab). Wavelength of light used is $5000\dot{A}$.

• A. $5\times {10}^{-6}m$
  
• B. $3\times {10}^{-6}m$
  
• C. $10\times {10}^{-6}m$
  
• D. $5\times {10}^{-5}m$

Answer 1

The correct option is A $5\times {10}^{-6}m$


According to the question, Shift = 5 fringe widths
$\Rightarrow \frac{(\mu -1)tD}{d}=\frac{5\lambda D}{d}$ $\therefore t=\frac{5\lambda }{\mu -1}=50,000\dot{A}$ =$5\times {10}^{-6}m$