Q. In Young’s double slit experiment, angular width of fringes is $0.20{^\circ}$ for sodium light of wavelength $5890\ \mathring{\mathrm{A}}$. If complete system is dipped in water, then angular width of fringes becomes
A) $0.11{^\circ}$
B) $0.15{^\circ}$
C) $0.22{^\circ}$
D) $0.30{^\circ}$
Explanation
(b) Angular fringe width $\theta = \frac{\lambda}{d} \Rightarrow \theta \propto \lambda$
$\lambda_{w} = \frac{\lambda_{a}}{\mu_{w}}$
So $\theta_{w} = \frac{\theta_{air}}{\mu_{w}} = \frac{0.20}{\frac{4}{3}} = 0.15{^\circ}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.