What can be measured using a dioptre meter?

If an object is placed between two plane mirrors inclined at an angle of $45^{\circ}$,then the number of images formed will be $9$. State whether this statement is True or False.

Where is the image formed when an object is placed between the principal focus $(F)$ and the center of curvature $(C)$ of a concave mirror?

Through which point of a convex lens does a ray of light pass without undergoing refraction?

The image formed by a concave mirror is real and of the same size. Where is the object placed?

If the radius of curvature of a spherical mirror is $30 \ cm$,what is its focal length (in $cm$)?