What is the $SI$ unit of the power of a lens?

The magnification equation is a relation between image distance and object distance.

One half of a convex lens of focal length $10\, cm$ is covered with a black paper. Can such a lens produce an image of a complete object placed at a distance of $30\, cm$ from the lens? Draw a ray diagram to justify your answer.
$A$ $4\, cm$ tall object is placed perpendicular to the principal axis of a convex lens of focal length $20\, cm$. The distance of the object from the lens is $15\, cm$. Find the nature,position and size of the image.

Which of the following statements is true for light waves?

What can be measured using a dioptre meter?

When an object is placed between the principal focus $(F)$ and the pole $(P)$ of a concave mirror,what kind of image is formed?