61.
What is refractive index ?

62.
A star appears twinkling in the sky because of

63.
What type of lens is used in a magnifying glass

64.
Time of exposure required for taking photograph of an object depends upon the

65.
A concave lens always forms

66.
A concave lens always forms an image which is

67.
Which one of the following determines the sharpness of image in a camera ?

68.
Dioptre is the unit of

69.
The part of the eye having the largest refractive index is :

70.
Vehicles use ________ to see the objects coming from behind.