Lesson Topics

1 | Mirrors

2 | The Law of Reflection

3 | Mirrors and Reflection of Light

4 | Mirrors and Image Formation

5 | Concepts Relating to Curved Mirrors

6 | Drawing Ray Diagrams for Concave Mirrors

7 | Drawing Ray Diagrams for Convex Mirrors

8 | Real and Virtual Images from Mirrors

9 | Summary

Lesson Summary

• Mirrors allows regular reflection of light to produce clear images.

• Plane mirrors have a flat surface.

• Concave mirrors have a surface that curves inwards.

• Convex mirrors have a surface that curves outwards.

• The law of reflection states that the angle of incidence is equal to the angle of reflection.

• The angle of incidence is the angle between the incident ray and the normal.

• The angle of reflection is the angle between the reflected ray and the normal.

• When parallel light rays reflect off a plane mirror, they remain parallel.

• When parallel light rays reflect off a concave mirror they converge.

• When parallel light rays reflect off a convex mirror they diverge.

• Plane mirrors reflect images that are upright and equal-sized.

• Concave mirrors reflect images that are upright and enlarged when close, and inverted and diminished when far away.

• Convex mirrors reflect images that are upright and diminished.

• Curved mirrors have surfaces shaped like a section of a sphere.

• The centre of curvature is the centre of the sphere.

• The radius of curvature is the radius of the sphere.

• The pole is the centre of the surface of the mirror.

• The principal axis is a straight line passing through the centre of curvature and the pole.

• The focal point is the point on the principal axis where reflected light rays converge (for concave mirrors) or appear to diverge (for convex mirrors).

• The focal length is the distance between the focal point and the pole.

• The focal point lies halfway between the centre of curvature and the pole; therefore, the focal length is half the length of the radius of curvature.

• Consequently, a gently curved mirror (with a longer radius of curvature) will have a longer focal length than a strongly curved mirror (with a shorter radius of curvature).

• Ray diagrams can be used to predict the size and orientation of images reflected by mirrors.

• Rules for drawing ray diagrams for concave mirrors:

• Light rays that are parallel to the principal axis will pass through the focal point after reflection.

• Light rays that pass through the focal point will become parallel to the principal axis after reflection.

• Rules for drawing ray diagrams for convex mirrors:

• Light rays that are parallel to the principal axis will appear to come from the focal point after reflection.

• Light rays that are directed at the focal point will become parallel to the principal axis after reflection.

• A real image is an inverted image formed in front of a mirror by light rays that converge after reflection.

• A virtual image is an upright image formed behind a mirror by light rays that diverge after reflection.

(Image: Giampaolo Trapasso, Wikimedia Commons)