(b) a concave lens behind it
   (c) a concave mirror in front of it
   (d) a concave mirror behind it
Ans: (d)
172. A spherical mirror is
   (a) a reflecting elliptical portion
   (b) a reflecting spherical surface
   (c) a parabolic reflecting surface
   (d) a flat reflecting surface
Ans: (b)
173. A series of east moving still pictures can be made to appear as a moving
   picture because the eye
   (a) can focus very rapidly as pictures change
   (b) is quicker than the brain
   (c) can see two images separated only if the interval" between seeing them is
       more than" one-tenth of a second
   (d) can shut out some of the light
Ans: (c)
174. When an incident beam of light strikes the surface of a glass slab
   normally, the refracted beam
   (a) goes straight through without bending
   (b) gets deviated away from the normal
   (c) gets bent towards the normal
   (d) gets reflected
Ans: (c)
175. Which of the following has the highest refractive index?
   (a) Crown glass
   (b) Water
   (c) Flint glass
   (d) Diamond
Ans: (d)
176. When light travels from one medium to another there is a change in its