In a double slit experiment the angular width of a fringe is found to be `0.2^(@)` on a screen placed I m away. The wavelength of light used in 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

Angular fringe separation,
`theta= (lambda)/(d) or d=(lambda)/(theta)`, In water, `d= (lambda')/(theta')`
`:. (lambda)/(theta)=(lambda')/(theta') or (theta')/(theta)=(lambda')/(lambda) = (1)/(mu)=(3)/(4)`
or `theta'=(3)/(4)theta=(3)/(4)xx0.2^(@)=0.15^(@)`