Playbook
Ray Optics
78 q - 1.50/paper - 29% HARD, and halved in 2025. Lenses and refraction are the core; the prism page is 47% HARD.
- Questions in the bank
- 78
- q/paper (2024–25 papers)
- 1.50
- Tagged HARD
- 29%
- Subtopics
- 5
Strand: Long Tail
When you’ll see it
A lens or mirror with an object distance, a slab or a liquid and apparent depth, a prism and its deviation, or a microscope or telescope.
How this chapter is tested
78 q at 1.50 a paper, 29% HARD — and it HALVED in 2025: 2.19 a paper across 2023-24, 1.08 across 2025. Still live, but no longer worth two questions of prep.
Lenses (24 q, 25%) and Refraction, Apparent Depth, and Total Internal Reflection (26 q, 27%) are the core. 1/v − 1/u = 1/f with the sign convention; power P = 1/f in metres; lenses in contact add their powers. Apparent depth is real depth over μ, and TIR needs sin C = 1/μ.
The prism page (17 q) is the most expensive at 47% HARD: minimum deviation μ = sin((A + δ)/2)/sin(A/2), and a thin prism deviates by (μ − 1)A.
The sub-skills
The distinct skills inside the chapter, in the order to learn them.
Lens and mirror formulas
Lens 1/v − 1/u = 1/f; mirror 1/v + 1/u = 1/f. Magnification v/u (lens) or −v/u (mirror).
Power and lensmaker
P = 1/f (m); in contact P = P₁ + P₂; lensmaker 1/f = (μ − 1)(1/R₁ − 1/R₂).
Refraction and TIR
Apparent depth = real/μ; critical angle sin C = 1/μ.
Prism
A = r₁ + r₂; minimum deviation μ = sin((A + δ_m)/2)/sin(A/2); thin prism δ = (μ − 1)A.
Traps to expect
Distractor shapes this chapter reuses. The Traps page covers the patterns that cut across chapters.
Dropping the sign convention
Object distances are negative in the Cartesian convention. A concave lens has negative f. One lost sign flips a real image to a virtual one.
A lens in a liquid keeps its focal length
Immersed in a liquid, (μ − 1) becomes (μ_lens/μ_liquid − 1), and the focal length grows. It can even change sign.
Learn it before you drill it
This chapter has full teaching notes — foundations, worked examples, self-checks and a per-subtopic mastery checkpoint. Read the notes once, then drill subtopic by subtopic below.
Ray Optics notesDrill every ray optics question
78 questions from the bank, scoped to 5 bundled subtopics.
Drill one subtopic at a time
The 5 subtopics this playbook covers, in catalog order.
Related playbooks
Often paired with this one — the technique, the trap or the taxonomy overlaps. Drill these next.