The phenomenon, which is not due to total internal reflection is

An achromatic convergent doublet of two lenses in contact has a power +2 D . The convex lens has power +5 D . The ratio of the dispersive powers of the convergent and divergent lenses is (in magnitude)

The length of the compound microscope is 15 cm . The magnifying power for relaxed eye is 25 . If the focal length of eye lens is 6 cm then the object distance for objective lens will be

A convex lens of focal length $\frac{1}{3} \mathrm{~m}$ forms a real, inverted image twice the size of the object. The distance of the object from the lens is