Give two uses of a convex lens.

An object is situated at $8 \, cm$ from a convex lens of focal length $10 \, cm$. Find the position and nature of the image. Draw a ray diagram to illustrate the formation of the image (not to scale).

What can be measured using a dioptre meter?

Two lenses have powers of $(a) +2 \text{ D}$ and $(b) -4 \text{ D}$. Find the nature and focal length of each lens.

You are given a convex lens of focal length $10\, cm$. Where would you place an object to get a real,inverted and highly enlarged image of the object? Draw a ray diagram.

Define $1$ dioptre of power of a lens.