In young's double slit experiment the separation `d` between the slits is `2mm`, the wavelength `lambda` of the light used is `5896 Å` and distance `D` between the screen and slits is `100 cm`. It is found that the angular width of the fringes is `0.20^(@)`. To increases the fringe angular width to `0.21^(@)`(with same `lambda` and `D`) the separtion between the slits needs to be changed to

Options

A. `1.8` mm
B. `1.9` mm
C. `2.1` mm
D. `1.7` mm

Answer

B

Explanation

Angular width `=(lambda)/(d)`
`0.20^(@)=(lambda)/(2mm)` …(i)
`0.21^(@)=(lambda)/(d)` …(ii)
Dividing we get, `(0.20)/(0.21)=(d)/(2mm)`
`:. d=1.9` mm.