The focal length of a convex lens is 20 cm.What is the power?

The focal length of a lens depends on

The focal length of convex lens is 20 cm. If an object of height 4 cm is placed at a distance of 30 cm from the lens, find: The magnification produced by the lens.

A comvex lens and a concave lens are placed in contact. The ratio of magnitude of the power of the convex lens to that of the concave lens is 4:3. If the focal length of the convex lens is 12 cm, then the focal length of the combination will be

An object is placed vertically at a distance of 20 cm from a convex lens .If the height of the object is 5 cm and the focal length of the lens is 10 cm, what will be the position, size and nature of the image? How much bigger will the image be as compared to the object?

Focal length of a convex lens is 20 cm and its R.I. is 1.5. It produces an erect, enlarged image if the distance from the object of the lens is

What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20 cm . Is the system a converging or a diverging lens ? Ignore thickness of the lenses.

Find the focal length of a convex lens which produces a real image at 60 cm from the lens when an object is placed at 40 cm in front of the lens .

The focal length of a concave lens with power -4D is______

Calculate the focal length of a corrective lens having power +2.5D.