Question

A divergent beam of light from a point source S, (having a divergence angle α), falls symmetrically on a glass slab as shown in Fig. The angle of incidence of the two extreme rays are equal. It the thickness of glass slab is t and its refractive index is n, the divergence angle of emergent beam, would be

(1) zero

(2) α

(3) sin^-1 (1/n)

(4) 2 sin^-1 (1/n)

Answer 1

(2) α

Fig. show refraction, through the glass slab, for incident rays SA and SB. The emergent ray CE is parallel to SA and the emergent ray DF is parallel to SB. The emergent rays appear to diverge from point S' . However the angle of divergence |ES'F also equals α.