Physics notesOptics & ModernRay Optics
Independent topic page
State one Cartesian sign convention on the figure, apply mirror/lens formula once per surface, then chain with magnification — combinations become sequential imaging under time pressure.
01. Snell: n₁ sin i = n₂ sin r. TIR when light in denser medium meets rarer with i > i_c = sin⁻¹(n₂/n₁).
02. Spherical mirror: 1/v + 1/u = 1/f with consistent signs; m = −v/u (Cartesian). Thin lens: 1/v − 1/u = 1/f (same sign discipline as your chosen convention).
03. Prism: δ = i + e − A; at minimum deviation μ = sin((A+δ_m)/2)/sin(A/2). Dispersion splits colours by μ(λ).
04. Combinations: image of first element is object for the next; track whether the intermediate image is real/virtual for the following optic.
05. One sign convention per solution, written on the figure. Mirror and lens formulas share structure but not identical sign habits—do not switch mid-way.
06. Image formation is sequential for combinations: image of first is object of second with distance shift. Magnification multiplies with sign tracking erect/inverted.
07. TIR only denser→rarer when i>i_c. Prism: μ=sin((A+δ_m)/2)/sin(A/2) at minimum deviation. Small-angle and paraxial assumptions are silent constraints.
Official · 2026
Official syllabus points for Ray Optics only — not the full Optics & Modern portion map. Portion hub: Optics & Modern · Optics analysis.
No topic-specific exclusions flagged — finish the unit points below for Ray Optics.
Source: https://jeeadv.ac.in/documents/jee-advanced-2026-syllabus.pdf
Exam focusMirrors, lenses, refraction, prism, and TIR — not interference/diffraction.
Syllabus points
2020–2026 paper weight
Topic match inside parent portion Optics (13.2% of Physics tags). Stats below are portion backdrop; matched subtopics show where Ray Optics sits.
Portion-wide type/difficulty mix lives on the Optics analysis — not repeated here so this page stays on Ray Optics.
01. Dominant subtopics: Ray Optics (19), Wave Optics (12).
Cross-topic stems
Advanced rarely asks a chapter in isolation. These are tagged multi-idea Physics stems that touch Ray Optics — practise the knowledge bridge, not only the single-chapter drill.
Step 1: for waves, check superposition/phase options individually. Step 2: for optics, ray-trace each claim (TIR, magnification, mirror/lens sign). Step 3: never assume ‘exactly two correct’ — mark only proven options.
Two consecutive MC items amplify partial-marking risk.
Practise MC pairs under a strict ‘prove or leave’ rule.
Step 1: finish photoelectric/nuclear arithmetic cleanly. Step 2: switch to ray-optics formulae (mirror/lens/prism) without reusing constants wrongly. Step 3: track significant figures as required by the grid.
Formula-dense corridor; one wrong sign convention costs two questions.
Keep a tiny optics sign-convention sticky note on your desk during NUM practice.
Why methods matter
Stamp one sign convention and image sequentially through combinations — silent sign flips cost Advanced Optics marks.
One stamp prevents mid-solution sign drift — the #1 Advanced optics failure.
Do thisWrite ‘Cartesian: incident direction +’ (or your school’s rule) on the figure before assigning u.
One stamp prevents mid-solution sign drift — the #1 Advanced optics failure.
Object on left, light→right: u negative for real object in standard Cartesian lens convention.
Turns ‘hard’ systems into repeated single-element solves.
Do thisFor combinations, finish optic 1 completely (v₁, nature), shift origin to optic 2, redefine u₂.
Turns ‘hard’ systems into repeated single-element solves.
Lens then mirror: use mirror image as object for return pass through lens if light retraces.
Many MC options hinge only on whether TIR occurs.
Do thisCheck i ≷ i_c before computing messy refraction angles.
Many MC options hinge only on whether TIR occurs.
From glass to air, i_c=sin⁻¹(1/μ); if i>i_c, no emergent ray.
Orientation follows sign of product without re-deriving.
Do thism_total = m₁ m₂ … with each m using that element’s u,v.
Orientation follows sign of product without re-deriving.
Two real inversions → erect final image if both m negative.
Processed examples
Read the impact line first. Then notice which family/model was chosen. The solution is written the way your rough sheet should look in the hall.
An object is 30 cm in front of a concave mirror of focal length 20 cm. Find image distance (Cartesian: incident light left to right, f negative for concave).
This stem rewards early recognition of the mirror / thin-lens formula model.
Model chosen1/v+1/u=1/f.
Answer60 cm in front (real)
Takeaway: Stamp the sign convention before substituting.
A thin prism of angle 4° has μ=1.5. Find deviation.
This stem rewards early recognition of the prism deviation and dispersion model.
Model chosenδ=(μ−1)A.
Answer2°
Takeaway: Thin-prism deviation is linear in A.
A thin equiconvex lens of focal length 20 cm has its rear surface silvered. An object is placed 30 cm in front of the unsilvered face. Find the final image position.
This Advanced-level variation couples hidden constraints with the combination of lenses/mirrors model.
Model chosenLight passes lens, reflects from mirror, passes lens again — equivalent to a mirror of f_eq.
Answer15 cm in front of the lens (real image)
Takeaway: Silvered lenses reduce to an equivalent mirror after one careful power sum.
Reusable models
Advanced stems cluster. Name the family in 10–15s, write the fast model, then run the same path. Do not invent a new plan each time.
Looks likeu–v–f with sign convention
Fast modelState sign convention once; 1/v−1/u=1/f (lens) or mirror form.
Recognition fixes the model before arithmetic begins.
Do not start blind expansion or casework before identifying the governing model.
Looks likeTwo thin lenses, silvered lens, or mirror+lens
Fast modelImage of first is object for second; track intermediate.
Recognition fixes the model before arithmetic begins.
Do not start blind expansion or casework before identifying the governing model.
Looks likeμ₁/u + … ; critical angle
Fast modelUse refraction formula; TIR when i>i_c=sin⁻¹(μ₂/μ₁).
Recognition fixes the model before arithmetic begins.
Do not start blind expansion or casework before identifying the governing model.
Looks likeδ=(μ−1)A; angular dispersion
Fast modelMinimum deviation relates μ to A and δ_m.
Recognition fixes the model before arithmetic begins.
Do not start blind expansion or casework before identifying the governing model.
Hall timing
Underline optical elements or modern-physics mode (ray, YDSE/diffraction/polarisation, photoelectric, Bohr, X-ray, nuclear). Note the exact ask and any sign-convention figure.
Write the governing relation once: mirror/lens formula with signs, path difference, Einstein equation, Bohr ΔE, Moseley/de Broglie, or decay law. Reject out-of-syllabus interference setups beyond YDSE.
Compute with one consistent convention and units (eV vs J, nm vs m). Carry magnification signs and decay exponents carefully.
Check limits (thin lens, small angle, λ≪a), energy/sign sense and syllabus scope. Multi-correct: test each statement alone.
After the model is locked
n₁ sin i = n₂ sin r; i_c = sin⁻¹(n_r/n_d)
Refraction and critical angle
1/v + 1/u = 1/f; f = R/2
Spherical mirror (Cartesian signs)
1/v − 1/u = 1/f; P = 1/f (f in m)
Thin lens in air
m = h′/h = −v/u (mirror/lens Cartesian)
Size and orientation
δ = i + e − A; μ = sin((A+δ_m)/2)/sin(A/2)
Triangular prism
1/f = (μ−1)(1/R₁ − 1/R₂)
Thin lens surfaces known
1/F = 1/f₁ + 1/f₂
Coaxial contact combination
Make it automatic