A lens is a transparent optical medium bounded by two surfaces; at least one of which should be spherical. Considering image formation by a single…

A lens is a transparent optical medium bounded by two surfaces; at least one of which should be spherical. Considering image formation by a single spherical surface successively at the two surfaces of a lens, lens maker's formula is obtained. It is useful to design lenses of desired focal length using surfaces of suitable radii of curvature. This formula helps us obtain a relation between $\displaystyle \mathrm{u}, \mathrm{v}$ and f for a lens. Lenses form images of objects and they are used in a number of optical devices, for example microscopes and telescopes.

An object AB is kept in front of a composite convex lens, as shown in figure. Will the lens produce one image ? If not, explain.

A real image of an object formed by a convex lens is observed on a screen. If the screen is removed, will the image still be formed ? Explain.

A double convex lens is made of glass of refractive index $\displaystyle 1.55$ with both faces of the same radius of curvature. Find the radius of curvature required if focal length is $\displaystyle 20$ cm .

Two convex lenses A and B of focal lengths $\displaystyle 15$ cm and $\displaystyle 10$ cm respectively are placed coaxially ' $\displaystyle d$ ' distance apart. A point object is kept at a distance of $\displaystyle 30$ cm in front of lens A . Find the value of 'd' so that the rays emerging from lens B are parallel to its principal axis.