(a) velocity
   (b) wavelength
   (c) frequency
   (d) Both (a) and (b) above
Ans: (d)
177. We see the sun before it actually rises on the horizon. This is due to
   (a) refraction
   (b) reflection
   (c) total internal reflection
   (d) parallax
Ans: (a)
178. The mirage is a phenomenon
   (a) generally considered as a desert happening
   (b) caused by unequal heating of the several layers of the atmosphere above
       the desert
   (c) in which the refracted rays take a curved path resulting in total internal
   (d) All the above
Ans: (d)
179. Diamond shines because of its
   (a) purity
   (b) hardness
   (c) high density
   (d) high refractive index and low critical angle
Ans: (d)
180. For viewing objects placed at a higher level from a position at a lower
   level, the instrument used" Is known aa
   (a) telescope
   (b) spectrometer
   (c) microscope
   (d) periscope
Ans: (d)