Question

1Which of these gives always a virtual image?
a)convex mirror b)plane mirror c)convex lens d)concave lens
2.The refractive index of kerosene &benzene are 1.44 & 1.50 . Then speed of light is more in ..........
3.The boiling point of water at higher altitudes.a) increases b) decreases
PLZ I need it immediately....

Answer 1

1) convex mirror diverges and reflects the rays falling on it, and hence it always gives a virtual image.
    Concave lens transmits the light rays to the other side and diverges them. So only a virtual image is formed.

2)
      Speed of light in a medium = speed of light in vacuum / refractive index 
 Since refractive index is less in Kerosene, the speed of light is more in kerosene.

3.
  The boiling point decreases at higher altitudes, as the atmospheric pressure of air is less. 

Answer 2

1. A Concave lens will always give a virtual image

2. the Ri of kerosene is less , so the speed of light in kerosene will be more.

3. the boiling point decreases,as atmospheric pressure decreases