Preferential filtering of light consisting of different wavelengths can be done using total internal reflection. The concept of filtering lies in the fact that different wavelengths have different refractive indices in a medium The beam of light with different wavelengths are made incident on an isosceles right angled prism as shown in the figure. The wavelength or wavelengths which satisfy the condition of totai internal reflection, theta sin ge(1/mu), get reflected Others get refracted, hence gets separated. G is the angle of incidence and u. is the refractive index .of the particular wavelength in that particular medium. Thus, by changing the medium and by changing the angles of the prism we can satisfy the condition df total internal reflection for a particular wavelength, which gets separated out. Q If hypothetically the density of the material is increased gradually, then which of the colour gets separated next?