Question

If a laser strikes a mirror with an angle of incidence of 36°, what is the angle between the angle of incidence and angle of reflection?

Answer 1

If you measure the angle of incidence from the normal, the angle of reflection will also be `36^0` for a total of `72^0`

However if the `36^0` you mention is the angle as measured from the plane of the mirror, then the angle of incidence (as measured from the normal) will be `90^0-36^0=54^0` and the total angle will be twice that `2*54^0=108^0`.

The normal is a line perpendicular to the surface of the mirror at the point where the incoming ray strikes. It is usual to measure the angles from the normal, as this makes calculations on curved mirrors a lot easier.

In those the normal is the line drawn from the centre of the sphere of which your (concave or convex) mirror is a part.