Select the alternatatives. (a) A diverging beam of light form a point source S having divergence angle alpha ,falls symmetrically on a glass slabas shown .the angles of incidence of the two extreme rays are equal .Fi the thickness of the glass slab is tand the refractive index nthe n the divergence angle of the emergent beam is (A) zero,(B) alpha(C ) sin^(-1)(1//n)(D) 2 sin^(-1)(1//n) (b) Arectangular glass slabABCDof refractive index n_(1) is immersed in water of refractive indexn_(2)(n_(1)gtn_(2)) A ray of light is incident at the surface ABof the slab as shown .The maximum value of the angle of incidenc ealpha_(max)such that the ray comes out only from the other surface CD is given by (A) "sin"^(-1)[(n_(1))/(n_(2))cos("sin"^(-1)n_(2)/n_(1))] (B)sin^(-1)[(n_(1))/(n_(2))cos("sin"^(-1)(1)/n_(2))] (C)sin^(-1)((n_(1))/(n_(2)))(D)sin^(-1)((n_(2))/n_(1)) (c) A point source of lightB is placed at a distance L inother of the centre of a mirror of width hung vertically onawall A man walks is front of the mirror along a line parallel to the mirror at a distance 2L from it as shown .the greatest distance over which he can see the image of the light source in the mirror is (A)d//2 (B) d,(c )2d,(d)3d, a hollow double concave lens is made of very thin transparents meterial .It can be filledwith air or either of two liquids L_(1)andL_(2)having refractive indicesn_(1)and n_(2)respectively(n_(2)gtn_(!)gt1) the lens will diverge a parallel beam of light of it is filled with (A)air and placed in air.(B) air and immersed inL_(1)(C ),L_(1) and immersed inL_(2) (D),L_(2) ans immersed in L_(1)