A beam of light of intensity I o falls normally on a transparent plane-parallel plate of thickness l. The beam contains all the wavelengths in the interval from λ1 to λ2 of equal spectral intensity. Find the intensity of the transmitted beam if in this wavelength interval the absorption coefficient is a linear function of λ, with extreme values x1 and x2. The coefficient of reflection at each surface is equal to p. The secondary reflections are to be neglected.