In a double slit experiment the screen is placed at a distance of 1.25m from the slits. When the apparatus is immersed in water , the angular width of the fringe is found to be `0.2^@`. When the experiment is performed in air width same set up, the angular width of the fringe is

Options

A. `0.4^@`
B. `0.27^@`
C. `0.35^@`
D. `0.15^@`

Answer

D

Explanation

When the apparatus is immersed in water the angular width of a fringe `theta= lamda/2 and theta=0.2^@`
and the angular width of a fringe in air
`theta.=(lamda.)/d `
`1/mu_w=(lamda.)/lamda`
`(lamda.)/lamda=3/4`
Now, `(theta.)/theta=(lamda.)/lamda`
`theta.=(lamda.)/lamda times theta`
`theta.=3/4 times 0.2^@`
`theta.=0.15^@`