The normal line is a line at a right angle (90 degrees) to the surface of an object

To draw a normal line to the mirror, you must draw a line at 90 degrees to the surface of the mirror.

Refraction of Light: as it passes from less dense to more dense mediums

Angle of Incidence - Definition, Formula, Diagram, Examples

Images formed by an object placed between two plane mirros whose reflecting surfaces an angle of 90^{circ} with one another lie on a

If the incident ray makes an angle of with the normal, then what is the angle of reflection? - Quora

A ray is deviated through 90° by a right angle prism. What should be the minimum refractive index of the material of the prism? - Quora

Reflection of light — Science Learning Hub

Is it possible to calculate the surface area of this triangle? : r/askmath

The normal line is a line at a right angle (90 degrees) to the surface of an object

Physics Tutorial: Right Angle Mirrors

Right Angle - Definition, Properties, Shape, Examples

Distance of object from mirror is: Distance of image

homework and exercises - Why do electric field lines start and end at 90 degree at the surface of a conductor? - Physics Stack Exchange