Question

In YDSE, water is filled in the space between the slits and screen. Then

• A. fringe pattern shifts upward but fringe width remains unchanged
• B. fringe width decreases and fringe pattern shifts upward
• C. fringe width remains unchanged and central fringe does not shift
• D. fringe width decreases and fringe pattern does not shift

Answer 1

Answer: (D)

fringe width decreases and fringe pattern does not shift

Fringe width $\beta =\frac{\lambda D}{d}$

If $\mu (>1)$ is 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 absence of sheet.