In Young's double slit experiment the separation of between the slits is `2mm`, the wavelength `lambda` of the ligth used is `5896Å` and distance D between the screen and slits is `100cm`.
It is found that the angular width of the fringes is `0.20^@`. To increase the fringe angular width to `0.216` (with same `lambda` and D) the separation between the slits needs to be changed to

Options

A. (a) `1.8mm`
B. (b) `1.9mm`
C. (c) `2.1mm`
D. (d) `1.7mm`

Answer

B

Explanation

`theta=lambda/dimpliestheta_1/theta_2=d_2/d_1`
`(0.20)/(0.21)=d_2/2implies(0.20)/(0.21)xx2=1.9mm`