State the laws of reflection. Draw a labelled diagram of a concave mirror showing P, F, C, R and f, and the reflection of two rays parallel to the principal axis.

1. 1 · Define reflection in one line. Reflection is the bouncing back of light from a shiny surface.
2. 2 · Write the two laws.
   • The angle of incidence equals the angle of reflection, both measured from the normal.
   • The incident ray, the normal and the reflected ray lie in the same plane.
3. 3 · Draw the labelled diagram. [Diagram: principal axis, concave mirror, P on the mirror, F halfway to C, R and f marked with arrows, two parallel rays reflected through F]
4. 4 · Write the relation. R = 2f, so F lies midway between P and C.
5. 5 · Link to daily life. Torch reflectors and dish-type solar cookers use this focusing by a concave mirror.
6. 6 · Close in one line. These laws apply to plane and spherical mirrors alike.

Scoring tip: Put an arrowhead on every ray and draw the normal as a dotted line. Unlabelled diagrams lose marks.