In a physics lab, light with a wavelength of 560nm travels in air from a laser to a photocell in a time of 16.9ns. When a slab of glass with a thickness of 0.850m is placed in the light beam, with the beam incident along the normal to the parallel faces of the slab, it takes the light a time of 21.6ns to travel from the laser to the photocell.
What is the wavelength of the light in the glass? Use 3.00*10^*m/s for the speed of light in a vacuum.