195. Holography is the technique of
   (a) taking photos of various objects
   (b) recording and reproducing three dimensional images
   (c) tracing out planets and stars in the sky
   (d) transmitting light waves
Ans: (b)
196. The image of an object formed in a plane mirror
   (a) is real
   (b) is virtual
   (c) can be obtained on a screen
   (d) is slightly bigger than the object
Ans: (b)
197. If an object is placed between two parallel plane mirrors, the number of
   images formed will be
   (a) 1
   (b) infinite
   (c) 0
   (d) 4
Ans: (b)
198. Sound travels fastest in
   (a) air
   (b) water
   (c) iron
   (d) vacuum
Ans: (c)
199. The velocity of sound in air
   (a) increases as the square root of the absolute temperature
   (b) decreases with temperature
   (c) is independent of temperature
   (d) None of these
Ans: (a)
200. In a longitudinal wave, the direction of propagation of the wave is