Problem Six. A double$-$slit experiment has slit spacing $0\mathrm{.}190$ mm and distance $1\mathrm{.}52$ m between the screen and the slits. $($THIS IS AN EXAM QUESTION.$)13.$ Find the fringe spacing between bright fringes $($in mm$)$ when $483$ nm light is used. $($A$)1\mathrm{.}50($B$)2\mathrm{.}43($C$)3\mathrm{.}86($D$)4\mathrm{.}37$ Problem Seven. Magnesium fluoride $($MgF$2)$ is used as an anti reflective coating on lenses. The index of refraction of MgF$2$ is $1\mathrm{.}39.$ Assume that the index of refraction of the coating is more than the index of refraction of the lens. $($THIS IS AN EXAM QUESTION.$)14.$ Find the thinnest film of MgF$2($in nm$)$ that works as an anti reflective coating for light near the center of the visible spectrum $($ $=510$ nm$).($A$)150($D$)378($B$)183($E$)456($C$)245($E$)5\mathrm{.}7$