A lens is called equi-convex or equi-concave when :

1. the radius of curvature of first surface of lens is greater than the radius of curvature of the second surface.
2. the radius of curvature of the second surface of the lens is greater than the radius of curvature of the first surface.
3. the radius of curvature of the two surfaces of the lens are equal.
4. none of the above

The focal length of a lens depends upon :

1. the refractive index of the material of lens relative to its surrounding medium
2. the amount of light entering the lens
3. the radius of curvature of the two surfaces of lens
4. both (1) and (3)

If half part of a convex lens is covered, the focal length …………… but the intensity of the image ……………

1. increases, decreases
2. decreases, increases
3. does not change, increases
4. does not change, decreases

The focal length of a thin convex lens is …………… than that of a thick lens.

1. less
2. more
3. same
4. none of the above