71.
Rainbow is produced when sunlight fall on drops of rain. Which of the following physical phenomena are responsible for this?

  1. I.Diffusion
  2. II.Refraction
  3. III.Internal reflection

72.
Natural radioactivity was discovered by

73.
Planets are

75.
Mica is used in electrical appliances such as electric iron because mica is

76.
It is easier to roll a barrel full of coal tar than to pull it because

77.
Minimum number of unequal vectors which can give zero resultant are

78.
Intensity of sound has

79.
Rain is falling vertically downwards. To a man running east-wards, the rain will appear to be coming from

80.
An aeroplane is flying horizontally with a velocity of 600 km/h and at a height of 1960 m. When it is vertically at a point A on the ground a bomb is released from it. The bomb strikes the ground at point B. The distance AB is