The cross-section of a glass prism is an equilateral triangle. The refractive index of the glass is 1.601 at a free-space wavelength of 0.4 μm and 1.569 at 0.7 μm. Show that if white light is incident on the prism at an angle of 40˚ to the surface normal, the spectrum from 0.4 to 0.7 μm will be dispersed over an angular width of 4.9˚.