In Young’s double slit experiment the separation d between the slits is 2mm, the wavelength $\mathrm{\lambda }$ of the light used is 5896A⁰ and distance D between the screen and slits is 100cm. It is found that the angular width of the fringes is 0.20⁰. To increase the fringe angular width to 0.210 (with same $\mathrm{\lambda }$ and D) the separation between the slits needs to be changed to