When an object is placed at $2F$ in front of a convex lens,where will its image be formed?

Copy the given figure and complete it to show the formation of the image of the object $AB$. Name the lens used in the figure.

Where is the object placed to observe it through a compound microscope?

Beams of light are incident through the holes $A$ and $B$ and emerge out of the box through the holes $C$ and $D$ respectively,as shown in the figure. Which of the following could be inside the box?

An object $3 \, cm$ high is placed at a distance of $20 \, cm$ in front of a convex lens of focal length $12 \, cm$. Find the position,nature,and size of the image formed.

The radius of curvature of a spherical mirror is half of the focal length.