In which one among the following cases the convex lens does not give a real image?

Irrespective of the position of the ob j ect on the principal axis a concave lens gives an image of nature ………

The midpoint of a thin lens is called

The distance between two focal points of a thin lens having focal length f is ………

A virtual erect image is formed when an object is placed on the principal axis of a convex lens …………

Which of the following is a lens formula?

The focal length of the lens ………

The focal length of the lens ……… in water

An air bubble in water behaves like a …………

The focal length of double concave lens kept in air with two spherical surfaces of radii  $R_{1}R\_1$ = 30 cm and $R_{2}R\_2$ = 60 cm

The refractive index of the glass which is symmetrical convergent lens if its focal length is equal to the radius of curvature of its surface …………

The radii of curvature of a double convex lens are 10 cm and 10 cm. Its refractive index is 1.5. The focal length is ……

The number of images formed by a lens made up of three different material is ………

When a lens of focal length f is cut in to two equal halves perpendicular to principal axis, then the focal length of each part of the lens is …………

The focal length of the plano – convex lens is 2R. Its radius of curvature is R then the refractive index of the material used is ………