A light wave travels through a pure SiO 2 , a glass medium. The meduim refractive index is 1.52 defined at its related  wavelength in (µm). What is the group velocity ,V g,  in (m/s) in (3 decimal) if the group indiex is N g = 1.461?                        Note: The speed of light is c= 3 x 10 8 (m/s), do not use the exponentiation (10 8) in your calcuation , but use it as c = 3 (108 m/s) to get a correct answer.