1. The dispersive power of glass is defined as the ratio(nf-nc)/(nd-1) where c, d and f are the frauhofer wavelengths. Find the approximate group velocity in glass whose dispersive power is 1/30 and nd =1.5 2. A soap film is formed suing a rectangular wire frame and held in a vertial plane. When illuminated normally by laser light at 632.8nm, one sees a series of localized interference fringes that measure15 per cm. Explain their formation. Ok so for 1, there is a n equation for another problem that is ued to calculate all the n-values, but I'm not sure if its used in all cases or just in that problem. It is n([tex]\lambda[/tex]) = 1.5255 + (4825)/[tex]\lambda[/tex]. Also don't really know how these numbers relate to calculating the group velocity if its Vg = Vp(1-(k/n)(dn/d[tex]\lambda[/tex])) As for 2, I really don't have any idea. Don't know where to start. Wouldn't mind a wee nudge in the right direction.