Question

In Young's double-slit arrangement, water is filled in the space between screen and slits. Then -

• A.
  
  fringe pattern shifts upwards, but fringe width remains unchanged
• B.
  
  fringe width decreases, and central bright fringe shifts upwards
• C.
  fringe width increases, and central bright fringe does not shift
• D.
  fringe width decreases, and central bright fringe does not shift

Answer 1

The correct option is D

fringe width decreases, and central bright fringe does not shift
There is no shift in central maxima, but fringe width decreases because,

Fringe Width $=\frac{\lambda D}{d}$
Since, $\mu (>1)$ is the refractive index of water, then wavelength reduces by $\mu$ factor

New fringe width ${\beta }^{\prime }=\frac{\lambda D}{\mu d}$

Therefore in water, fringe width decreases, but there would be no lateral shift in fringe pattern due to the absence of a sheet.