a$)$ in a youngs double slit experiment, it is found that ten bright intereference fringes span a distance of $1\mathrm{.}8$ cm on a screeen placed $1\mathrm{.}0$ m away. The separation of the two slits is $0\mathrm{.}3$ mm$.$ Determine the wavelength of the light. b$)$ light from a helium$-$neon laser with wavelength $633$ nm is incident upon two very narrow slits spaced $0\mathrm{.}5$ mm