Question

A plate of thickness t made of a material of refractive index $\mu$ is placed in front of one of the slits in a double-slit experiment. What should be the minimum thickness t which will make the intensity at the centre of the fringe pattern zero?

• A. $(\mu -1)\frac{\lambda }{2}$
  
• B. $(\mu -1)\lambda$
  
• C. $\frac{\lambda }{2(\mu -1)}$
  
• D. $\frac{\lambda }{(\mu -1)}$

Answer 1

The correct option is C $\frac{\lambda }{2(\mu -1)}$


Intensity at the centre will be zero if path difference is $\frac{\lambda }{2}$. That is,
$(\mu -1)t=\frac{\lambda }{2}$ or $t=\frac{\lambda }{2(\mu -1)}$