Two convex lenses of focal lengths `f_1 ` and `f_2` respectively are placed in contact each other. Then what will be power of their equivalent lens?

Two convex lenses of focal lengths f_(1) and f_(2) respectively are placed in contact with each other. Then what will be power of their equivalent lens?

Two thin lenses of focal lengths 20 cm and 25 cm are placed in contact. The effective power of the combinations is

A convex lens of focal length 80 cm and a concave lens of focal length 50cm are placed in contact. The resulting will be—

Two identical equiconvex lenses, each of focal length f, are placed side by side in contact with each other with a layer of water in between them as shown in the figure. If refractive index of the material of the lenses is greater than that of water, how the combined focal length F is related to f?

Two lenses of focal lengths 6cm and 50 cm are used in construction of a telescope. Which lens will be used as an objective and why?

Two convex lenses of focal length 1.5 cm and 9 cm are arranged to form a microscope . A small object is placed 1.8 cm from the objective. If the image appears to be 37.5 cm from the eyepiece, what will be the distance between the objective and the eyepiece ?

Thin converging lenses of focal lengths 2 cm and 10 cm are used respectively as the objective and the eyepiece of a microscope. The distance between the optical centre of the lenses is 26 cm . If an object is placed at a distance of 2.25 cm from the objective , find the position and magnification of the final image.

An object is placed 30 cm away from a convex lens of focal length 10 cm and a sharp image is formed on a screen. Now a concave lens is placed in contact with the convex lens. The screen now has to be moved by 45 cm to get a sharp image again. The magnitude of focal length of the concare lens is (in cm)

A convex lens of focal lengths 30 cm produces 5 times magnified real image of an object What is the object distance ?