CBSE Class 12-science Answered
A biprism consist of two acute angled prism with their bases in contact.S is a narrow vertical slit illuminated with a monochromatic source of light .S is kept at a short distance from the biprism. The light falling on the lower half of the biprism bends upwards and appears to come from S2. Light falling on the upper half of the biprism bends downwards and appear to come from S1. The virtual images S1 and S2 formed by refraction act as coherent sources.The light from the virtual sources overlap and interference fringes are seen there on the screen which is at a distance from the coherent sources.