Question

In an ideal double-slit experiment, when a glass-plate $(\mu =1.5)$ of thickness t is introduced in the path of one the interfering beams (wavelength $\lambda$), the intensity at the position where the central maximum occurred previously remains unchanged. The minimum thickness of the glass-plate is :

• A. $\lambda$
• B. $\frac{\lambda }{3}$
• C. $\frac{2\lambda }{3}$
• D. $2\lambda$

Answer 1

The correct option is D $2\lambda$

According to the given condition,

$(\mu -1)t=n\lambda$ for minimum $t,n=1$

So, $(\mu -1)t_{min}=\lambda$

$t_{min}=\frac{\lambda }{\mu -1}$

$t_{min}=\frac{\lambda }{1.5-1}=2\lambda$