Question

Three light rays red (R), green (G) and blue (B) are incident on a right angled prism ‘abc’ at face ‘ab’. The refractive indices of the material of the prism for red, green and blue wavelengths are 1.39, 1.44 and 1.47 respectively. Out of the three which colour ray will emerge out of face ‘ac’? Justify your answer. Trace the path of these rays after passing through face ‘ab’.

Answer 1

For no emergence, the refractive index n should be greater than \(\frac{1}{sin\ c}\)

So the blue and green lights cannot emerge because their refractive index is more than 1.414 (n_g = 1.44, n_B = 1.47), and will suffer total internal reflection and only red light can emerge out because nr < 1.41. The path of these rays is shown in Fig.