A plate of thickness  $\text{'}t\text{'}$ made of a material of refractive index  $\text{'}\mu \text{'}$ is placed in front of one of the slits in a double slit experiment. What should be the minimum thickness  $\text{'}t\text{'},$ which will make the intensity at the centre of the fringe pattern zero?

• A

  $\frac{\left(\mu -1\right)\lambda }{2}$

• B

  $\frac{\lambda }{\left(\mu -1\right)}$

• C

  $\frac{\lambda }{2\left(\mu -1\right)}$

• D

  $\left(\mu -1\right)\lambda$