In a double-slit experiment the angular width of the fringe is found to be `0.2^(@)` on a screen placed 1 m away. The wavelength of light used is 600 nm. What will be the angular width of the fringe if the entire experimental apparatus is immersed in water ? Take refractive index of water to be `4//3`?

Explanation

Here, `theta_(1)=0.2^(@), D=1m, lambda_(1)=600nm, theta_(2)=?, mu=4//3`
`(theta_(2))/(theta_(1))=(lambda_(2))/(lambda_(1))=1/mu=3/4 Rightarrow theta_(2)=3/4 theta_1=3/4xx0.2^(@)=0.15^@`