Reflection, Refraction and Dispersion: One Sign Convention, Every Image

In the paper

Unit 3 carries 8 of the 50 physics marks; with six chapters sharing them, this one averages a little over one (MEC publishes weights by unit, not by chapter). That average understates the work: this is the largest single chapter in the physics syllabus, because three scope lines hold mirrors, refraction at plane surfaces, total internal reflection, prisms, lenses and dispersion between them, and nearly every item in that list is a formula you can be handed numbers for.

The MEC scope lines are: Reflection at curved mirrors; Refraction at plane surfaces and in lenses; Dispersion, chromatic aberration and achromatism. The headings below are those points, in MEC's order.

Three ways it is asked: recall (the critical angle of diamond, the unit of lens power, what dispersive power measures); understanding (why a convex mirror is chosen for a rear-view mirror, why a pond looks shallower than it is, why a glass lens grows weaker in water, why violet deviates most through a prism); application (a mirror or lens numerical worked with signs, a power in dioptres, a refractive index from minimum deviation, an angular dispersion, an achromatic pair).