Can a plane mirror be called a spherical mirror?

The focal length of a concave mirror is $30 \, cm$. Find the position of the object in front of the mirror so that the image is three times the size of the object.

What is the lens placed near the eye in a compound microscope called?

What is the wavelength range of visible light?

What type of mirror is used to obtain a real image?

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?