posted by Lara .
A light beam containing red and violet wavelengths is incident on a slab of quartz at an angle of incidence of 50.0°. The index of refraction of quartz is 1.455 at 660 nm (red light), and its index of refraction is 1.468 at 410 nm (violet light). Find the dispersion of the slab, which is defined as the difference in the angles of refraction for the two wavelengths.
I understand I need to use n1*sin theta 1 equals n2 * sin theta 2.
But how do I get theta's from wavelength to put into the equation?