7. In Young’s double slit experiment, the fringe width is found to be 0.4 mm. If the whole apparatus is immersed in water of refractive index 4⁄3 , without disturbing the geometrical arrangement, the new fringe width will be ?

7. In Young’s double slit experiment, the fringe width is found to be 0.4 mm. If the whole apparatus is immersed in water of refractive index 4/3 , without disturbing the geometrical arrangement, the new fringe width will be ?

(a) 0.30 mm

(b) 0.40 mm

(c) 0.53 mm

(d) 450 microns

Answer :  (a) 0.30 mm

\(\beta_{\text{medium}} = \frac{\lambda_{\text{medium}} D}{d}\)

\( = \frac{\lambda}{\mu} \cdot \frac{D}{d}\)

\( = \frac{\beta}{\mu}\)

\( = \frac{0.4 \,\text{mm}}{\tfrac{4}{3}}\)

\( = 0.3 \,\text{mm}\)