State and define the SI unit of power of a lens.

A boy with a mouth 5cm wide stands 2m away from a plane mirror. Where is his image and how wide is the image of his mouth?

‘‘A concave mirror of focal length 15cm can form a magnified erect as well as inverted image of an object placed in front of it.’’ Justify this statement stating the position of the object with respect to the pole of the mirror in both cases for obtaining the images.

Name the type of mirror used by dentists. How does it help?

An object lies at a distance of 2f from a concave lens of focal length f. Draw a ray-diagram to illustrate the image formation.

A 5cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 18cm at a distance of 12cm from it. Use lens formula to determine the position, size and nature to the image formed.

A large concave mirror has a radius of curvature of 1.5m. A person stands 10m in front of the mirror. Where is the person’s image?

If the image formed by a spherical mirror for all positions of the object placed in front of it is always erect and diminished, what type of mirror is it? Draw a labelled ray diagram to support your answer.

A lens has a focal length of, -10cm. What is the power of the lens and what is its nature?

Draw ray diagrams showing the image formation by a convex mirror when an object is placed:
At infinity.