Many optical instruments consist of a number of lenses.They are combined to increase the magnification and sharpness of the image. the net power (P) of the lenses placed in contact is given by the algebraic sum of the powers of the individual lenses `P_1,P_2,P_3`....as
`P=P_1 + P_2 + P_3` .....
This is also termed as simple additive property of the power of lens,widely used to design lens system of cameras,microscopes and telescopes.These lens systems can have a combinatio of convex lenses and also concave lenses.
(c) Draw a ray daigram to show the nature and position of an image formed by a convex lens of power +0.1D,when an object is placed at a distance of 20cm from its optical centre.