Question

In YDSE, find the thickness of 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 5th bright fringe was lying earlier (before inserting the slab). Wavelength of light used is $5000\mathring{A}$.

• 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

Answer: (A)

$5\times {10}^{-6}m$

Lateral shift $\overline{X}=\frac{\beta }{\lambda }(\mu -1)t=5\beta$

$t=\frac{5\beta \lambda }{\beta (\mu -1)}=\frac{5\times 5000\times {10}^{-10}}{(1.5-1)}=5\times {10}^{-6}m$