An optician prescribes a corrective lens of power $+2.0 \,D$. The focal length of the required convex lens is:

In many experimental set-ups,the source and screen are fixed at a distance $D$ and the lens is movable. Show that there are two positions for the lens for which an image is formed on the screen. Find the distance between these points and the ratio of the image sizes for these two points.

$A$ lens is placed between a source of light and a wall. It forms images of area $A_1$ and $A_2$ on the wall for its two different positions. The area of the source of light is

Write the lens formula for a thin lens.

$A$ biconvex lens has a focal length $2/3$ times the radius of curvature of either surface. The refractive index of the material is:

$A$ convex lens produces a real image $m$ times the size of the object. What will be the distance of the object from the lens?