Question

In a Young's double slit experiment, the fringe width is found to be 2 mm, when light of wavelength 6000 $\mathring{A}$ is used. find the change in fringe width if the whole apparatus is immersed in water of refractive index $\mathrm{1.33.}$

• A. $0.5mm$
• B. $1mm$
• C. $1.5mm$
• D. $2mm$

Answer 1

The correct option is C $1.5mm$

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

When immersed in water, the wavelength becomes ${\lambda }^{\prime }=\frac{\lambda }{\mu }$

Thus the new fringe width $={\beta }^{\prime }=\beta \times \frac{{\lambda }^{\prime }}{\lambda }=\beta \times \frac{1}{\mu }=1.5mm$