LENS

Assertion:A convex lens and a concave lens are kept in contact. They will behave as a diverging lens if focal length of convex lens is more. Reason: Power of a concave lens is always less than the power of a convex lens, as power of concave lens is negative whereas power of convex lens is positive.

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 kept at 60 cm from a lens gives a virtual image at 20 cm in front of the lens. What is the focal length of the lens ? It it a converging lens or diverging lens ? Also find the magnification produced.

An object to the left of a lens is imaged by the lens on a screen 30cm to the right of the lens. When the lens is moved 5cm to the right, the screen must be moved 5cm to the left to refocus the images. The focal length of lens is :-