A achromatic combination is made with a lens of focal length `f` and dispersive power `omega` with a lens having dispersive power of `2omega` . The focal length of second will be

The power of a lens having a focal length of 1 cm is

A converging system of convex lenses free from chromatic aberration and of focal length 2.5 cm is to be constructed by using a convex lens of focal length 2 cm and dispersive power 0.04 and another convex lens of dispersive power 0.03. What should be the focal length of the second lens and at what distance from the first lens should it be placed ?

The power of a lens with focal length 20 cm is………………

The power of a lens of focal length 0.5 m is :