Question
In Young's double slit experiment the separation $d$ between the slits is $2\,\, mm,$ 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^o $ . To increase the fringe angular width to $0.21 ^o $ (with same $\lambda$ and $D$) the separation between the slits needs to be changed to ......$mm$

