Thin Lenses

Consider the arrangement of thin lenses as shown in the figure. An object O is placed at a distance of mR from the system of thin lenses. From the lens system a plane mirror is placed at an unknown distance as shown for what value of m image of O and object O will coincide with each other. Consider paraxial rays approximation to be valid.

Two coaxial thin lenses are placed in contact with each other and a small object is placed at a distance of 20cm from the combination of lenses. The focal length of each lens is 30 cm. What will be the distance between the object and the image when both the lenses are (i) convex (ii) concave

Two thin lenses, aone convex of focal length 10 cm and other concave lens are kept in contact to form a composite lens of focal length 13 cm . If the combination acts as a converging lense the focal length of second lens is

Power (P) of a lens is given by reciprocal of focal length (f) of the lens. i.e. P = 1//f . When f is in metre, P is in dioptre. For a convex lens, power is positive and for a concave lens, power is negative. When a number of thin lenses of powers p_(1), p_(2), p_(3).... are held in contact with one another, the power of the combination is given by algebraic sum of the powers of all the lenses i.e., P = p_(1) + p_(2) + p_(3) + ........ Answer the following questions : Two thin lenses are in contact and the focal length of the combination is 80 cm . If the focal length of one lens is 20 cm , the focal length of the other would be

Two thin converging lenses of focal length 15 cm and 30 cm are held in contact with each other. The focal length of the combination is

Two identical thin converging lenses are kept in contact at a distance 12.5 cm from an object. If image produced is 4 times enlarged then what is the optical power of each lens. [5D]