Optics JEE Main PYQ — The Silvered-Lens and Fringe-Shift Traps That Decide This Block (2015-2026)
Optics JEE Main PYQ (2015-2026). Ray Optics is the highest-weightage chapter, the silvered-lens power trap, the sign-convention reference, the YDSE archetypes, and 15 PYQs.
The Single Highest-Weightage Chapter in JEE Physics. And It Punishes One Wrong Sign.
Ray Optics is now the single highest-weightage individual chapter in JEE Main Physics — the volume jumped ~146% in 2025 (from 20 questions to 42), and combined with Wave Optics the block reliably carries up to 12 marks, 2-3 questions, in virtually every shift. If you're triaging Physics, this block is where the marks concentrate.
But it's a high-ROI, high-penalty chapter. Unlike Modern Physics, which yields quick formula answers, Optics demands spatial awareness, procedural discipline, and rigorous algebra. The Cartesian sign convention is the primary filter — the examiners design NVQ answers and MCQ distractors around specific sign errors. And since 2025, Optics fills 20-30% of the compulsory NVQ section, where one wrong sign is −1 with no options to check against.
Two archetypes dominate. On the Ray side, the silvered lens (light passes through the lens twice: P = 2P_L + P_M). On the Wave side, YDSE — coinciding maxima for two wavelengths, and the fringe shift when a slab covers one slit. We analysed 180+ Optics questions across every JEE Main shift from 2015 to 2026. This is Logic Bloom's eleventh JEE Main analysis and fifth Physics chapter, after Mechanics, Modern Physics, and SHM & Waves.
| 🎯 We analyzed 180+ JEE Main Optics questions. The app has them all — ready to play and practice. | |
|---|---|
| This block is won by drilling multi-step setups until the sign convention and the image-tracing are automatic. Logic Bloom's Playground turns it into interactive practice: trace rays through a silvered lens, move an object and watch the image flip real-to-virtual, slide a slab across one YDSE slit and see the fringes shift, build a two-lens system and track the intermediate image. Then drill every PYQ including the compulsory NVQ type. When a sign-convention slip or a 2P_L+P_M error catches you, TarQ teaches the fix, and your Mistake Book logs it. | Get the app → Free to start. |
Sub-Topic Frequency: Lenses Lead Ray, YDSE Owns Wave
| Sub-topic | Share | Focus |
|---|---|---|
| Ray: Lenses & combinations | ~39% | Silvered lenses, equivalent focal length, spaced lenses |
| Ray: Refraction at curved surfaces & TIR | ~23% | Single-surface refraction, critical angle |
| Ray: Prisms | ~19% | Minimum deviation, grazing emergence |
| Ray: Spherical mirrors | ~15% | Longitudinal magnification (moving objects) |
| Wave: Interference / YDSE | ~75% of Wave | Coinciding maxima, slab fringe-shift, intensity ratios |
| Wave: Diffraction | ~15% of Wave | Single-slit central maximum, nth minimum |
| Wave: Polarisation | ~10% of Wave | Malus's law cascades, Brewster's angle |
Lenses and combinations are the undisputed core of Ray Optics — dominated by the silvered-lens archetype and lenses separated by a gap (where you can't use the simple additive power rule). On the Wave side, YDSE is ~75% of everything — the slab shift and coinciding maxima generate the clean integer answers NVQs love. Optical instruments have collapsed to ~4% since resolving power was deleted.
The Format That Raised the Stakes: Optics Fills a Third of the NVQs
| Era | NVQ Rule | Effect on Optics |
|---|---|---|
| Pre-2025 | Attempt any 5 of 10 | Students SKIPPED Optics NVQs (sign-error risk) |
| 2025-2026 | All 5 compulsory, −1 marking | Optics = 20-30% of Physics NVQs; no escape |
You can no longer dodge Optics numericals. When students could choose, they avoided Optics NVQs precisely because the sign convention is so easy to fumble. Now every one is compulsory and penalised — critical angle, apparent depth, intensity ratios all translate cleanly into numerical entry, and Optics has become a primary tool for the NTA to separate top-percentile candidates on precision alone.
| 🎯 A silvered lens is NOT P_L + P_M. Light passes through the lens TWICE, so it's 2P_L + P_M. And when it's in liquid, use the RELATIVE refractive index. Two traps in one question. | |
|---|---|
| The silvered-lens trap — the single biggest source of lost Ray Optics marks. A lens silvered on one face becomes a mirror-equivalent system, and light goes lens → mirror → lens — through the lens TWICE. So the equivalent power is P = 2P_L + P_M, not the naive P_L + P_M. Miss the factor of 2 and every downstream number is wrong. The second layer: when the silvered lens sits in a liquid, P_L must use the relative refractive index (μ_lens / μ_liquid), not the air value — students default to the air formula and the answer collapses. And for the "image forms on the object itself" (autocollimation) variant, the object goes at the CENTRE OF CURVATURE of the equivalent mirror (u = 2F_eq), not at its focus. Logic Bloom's Playground lets you silver a lens and trace the double pass so the 2P_L+P_M structure is visible — with TarQ explaining the relative-index correction. Then drill every PYQ and let your Mistake Book catch the silvered-lens slips. | Silver the lens → Free to start. |
The Cartesian Sign Convention — The Primary Filter
| 🎯 Get This Wrong and Everything Downstream Fails | ||
|---|---|---|
| Rule | Mirror | Lens |
| Formula | 1/v + 1/u = 1/f | 1/v − 1/u = 1/f |
| Magnification | m = −v/u | m = v/u |
| Real object (u) | Negative | Negative |
| Real image (v) | Negative (in front) | Positive (behind) |
| Virtual image (v) | Positive (behind) | Negative (in front) |
| m sign | Negative = real, inverted; Positive = virtual, erect | |
The origin is the pole/optical centre; incident-light direction is +x. The classic NVQ trap: "3× magnified REAL image" means m = −3 (not +3), and the object-image distance uses absolute values. Set the sign wrong at the start and the focal length comes out with the wrong sign — a −1.
The Young's Double-Slit Reference — Where Wave Marks Live
| 🎯 YDSE Core Reference | |
|---|---|
| Fringe width | β = λD/d (in a medium: β/μ, since λ shortens) |
| Path difference | Δx = d sinθ ≈ yd/D |
| Bright / dark | Bright: Δx = nλ; Dark: Δx = (n−½)λ |
| Intensity | I = I_max cos²(φ/2), where φ = (2π/λ)Δx |
| Slab shift (one slit) | Δy = (μ−1)t · D/d, TOWARD the covered slit |
| Coinciding maxima | n₁λ₁ = n₂λ₂ → lowest integers |
Two traps here. The slab shift: the pattern moves TOWARD the slit the slab covers, and the extra optical path is (μ−1)t — students forget to subtract the geometric thickness. And in the intensity formula it's cos²(φ/2), the HALF angle — dropping the half is a classic error. For coinciding maxima, find the lowest integers satisfying n₁λ₁ = n₂λ₂.
The Refraction & TIR Reference
| 🎯 Snell, Critical Angle, Apparent Depth | |
|---|---|
| Snell's law | μ₁ sinθ₁ = μ₂ sinθ₂ |
| Critical angle (TIR) | sinθc = μ_rarer/μ_denser; light must start in the denser medium |
| Apparent depth | d_app = d_real/μ (viewing from rarer, e.g. coin in water looks closer) |
| Wavelength in medium | λ ∝ 1/μ (λ SHORTENS in a denser medium) |
The apparent-depth direction trap: looking from rarer INTO denser (person → coin in water), the object looks closer — divide by μ. But looking from denser INTO rarer (fish → bird in air), the object looks FARTHER — multiply by μ. Students divide both ways. And TIR only happens going denser → rarer.
The Five Traps That Cost Marks
| 📌 Where Candidates Lose Marks (−1 Each Under NVQ) | |
|---|---|
| 1. Silvered-lens power | It's 2P_L + P_M (double pass), not P_L + P_M. In liquid, use relative μ for P_L. |
| 2. Sign convention | Real image in a mirror is negative v; "3× magnified real" means m = −3. One wrong sign flips f. |
| 3. Slab fringe-shift | Δy = (μ−1)t·D/d, toward the covered slit. Extra path is (μ−1)t, not μt. |
| 4. Single-slit vs YDSE width | Single-slit central max = 2λD/a (the factor of 2); YDSE fringe = λD/d. Don't swap. |
| 5. Apparent-depth direction | Rarer→denser divides by μ (closer); denser→rarer multiplies by μ (farther). |
The 15 Exam-Critical Formulas
| 📌 Lock These Cold | |
|---|---|
| Mirror / lens | 1/v+1/u=1/f (mirror); 1/v−1/u=1/f (lens); P=1/f (metres) |
| Lens maker | 1/f = (μ_rel−1)(1/R₁−1/R₂) |
| Silvered lens | P = 2P_L + P_M |
| Spaced lenses | P = P₁ + P₂ − dP₁P₂ |
| Single spherical surface | μ₂/v − μ₁/u = (μ₂−μ₁)/R |
| Prism | δ = (μ−1)A (thin); μ = sin((A+δm)/2)/sin(A/2) |
| Dispersive power | ω = (μᵥ−μᵣ)/(μ−1) |
| YDSE | β = λD/d; single-slit central max = 2λD/a |
Cross-Chapter Integration (the Real Difficulty)
| Combination | What It Tests |
|---|---|
| Optics + Modern Physics | Use λ from a YDSE fringe width to find the stopping potential of a photoelectric surface. |
| Optics + Kinematics | Speed of an image in a convex rear-view mirror: v_image = −m²·v_object (longitudinal magnification). |
| Ray + Wave (internal) | A convex lens after the double slits focusing the interference pattern at its focal plane. |
| Optics + Waves | Superposition principles underpinning interference and the intensity formula. |
JEE Main 2027 / 2028 Predictions
Predictions exclude the deleted resolving power of instruments.
Top 5 Sub-Topics Most Likely to Appear
| # | Predicted Topic | Why |
|---|---|---|
| 1 | Silvered lens immersed in fluid | Forces the relative-refractive-index correction — kills rote air-formula recall. |
| 2 | Spaced lenses (sequential refraction) | Trace the intermediate image; can't use the simple additive-power rule. |
| 3 | TIR with coated prisms | Critical angle becomes sinC = μ_film/μ_prism, not 1/μ_prism. |
| 4 | YDSE coinciding fringes | Integer/LCM logic — perfect for numerical entry. |
| 5 | Malus's law cascades | Three-plus polarisers at progressive angles. |
2 Dormant Concepts Due for Return
| Concept | Likely Format |
|---|---|
| Displacement method | f = (D²−x²)/4D — ties into the retained Experimental Skills section. |
| Newton's formula | xy = f² (distances from the focal points) — a shortcut for specific NVQs. |
Optics JEE Main PYQs — 15 Questions You Must Attempt
These 15 span 2015-2026 and reflect JEE's exact difficulty and NVQ style. Each has a worked one-line solution and the trap explained. (No resolving power — off-syllabus now.)
| 📌 15 Must-Attempt JEE Main Optics PYQs | |
|---|---|
| 1. Critical Angle (2026 Jan) | Light: medium A (2.4×10⁸ m/s) → B (2.7×10⁸). Critical angle? Answer: sin⁻¹(8/9). Solution: sinC = v_A/v_B = 2.4/2.7 = 8/9. Trap: Writing v_B/v_A (>1); light must go slow→fast for TIR. |
| 2. Mirror Focal Length (2026 Jan, NVQ) | Object and 3× magnified REAL image 40 cm apart. Focal length? Answer: −15 cm. Solution: m=−3→v=3u; |v|−|u|=40→u=−20,v=−60; f=−15. Trap: Taking m=+3 or skipping absolute values. |
| 3. Silvered Lens in Liquid (2025 Jan, NVQ) | Plano-convex (μ=1.5) in liquid (μ=1.2), plane side silvered, acts as concave mirror F=0.2 m. Find R. Answer: 0.10 m. Solution: P=2P_L; P_L=(1.5/1.2−1)/R; 1/0.2=0.5/R→R=0.10. Trap: Using air μ instead of relative (1.5/1.2). |
| 4. Coinciding Maxima (2025 Jan, NVQ) | YDSE 650 & 550 nm, D=1.2 m, d=2 mm. Least distance where bright fringes coincide? Answer: 4.29×10⁻³ m. Solution: n₁·650=n₂·550→11:13; y=11·650n·D/d. Trap: Pairing the wrong integer with each wavelength. |
| 5. Grazing Emergence (2026 Jan, NVQ) | Equilateral prism μ=√2, ray grazes the second face. Angle of refraction at first face? Answer: 15°. Solution: r₂=C=45°; A=r₁+r₂=60°→r₁=15°. Trap: Solving for the angle of incidence, not r₁. |
| 6. Intensity Ratio (2024 Jan) | YDSE path difference 7λ/4. I/I_max? Answer: 1/2. Solution: φ=(2π/λ)(7λ/4)=7π/2; I=I_max cos²(7π/4)=I_max/2. Trap: Forgetting the half-angle in cos²(φ/2). |
| 7. Autocollimation (2025 Apr) | Convex lens (μ, R), one side silvered. Object placed where image forms on itself? Answer: R/2(2μ−1). Solution: P_eq=2·[2(μ−1)/R]+2/R=2(2μ−1)/R; u=2F_eq. Trap: Placing object at F instead of 2F of the equivalent mirror. |
| 8. Single Surface (2026 Jan, NVQ) | Parallel beam hits convex glass surface R=50 cm, μ=1.5. Convergence distance? Answer: 150 cm. Solution: 1.5/v − 0 = 0.5/50 → v=150. Trap: Using the lens-maker formula instead of single-surface refraction. |
| 9. Three Polarisers (2024 Jan, NVQ) | Unpolarised through P₁, P₃ crossed, P₂ at 45°. Output = I₀/x. Find x. Answer: 8. Solution: I₀/2 → ×cos²45 → ×cos²45 = I₀/8. Trap: Forgetting the first polariser halves unpolarised light. |
| 10. Slab Fringe Shift (2021 Mar, NVQ) | Slab μ=1.4 before one slit shifts pattern 0.3 cm, D=60 cm, d=1.5 mm. Thickness? Answer: 11.25 μm. Solution: Δy=(μ−1)t·D/d → t=11.25×10⁻⁶ m. Trap: cm/mm/μm unit conversion. |
| 11. Slit-Width Intensity (2019 Apr) | YDSE slit-width ratio 4:1. I_max/I_min? Answer: 9:1. Solution: I∝width→a₁/a₂=2; (2+1)²/(2−1)²=9. Trap: Using (4+1)²/(4−1)²=25/9 (confusing width with amplitude). |
| 12. Wavelength in Medium (2026 Jan, NVQ) | λ in water (μ=4/3) is 540 nm. λ in μ=3/2 medium? Answer: 480 nm. Solution: λμ constant: 540·(4/3)=λ·(3/2)→480. Trap: Multiplying by μ (assuming λ grows in denser media). |
| 13. Single-Slit Minima (2024 Jan, NVQ) | First diffraction minima at 30°, a=xλ. Find x. Answer: 2. Solution: a sin30=λ→a=2λ. Trap: Using the YDSE bright-fringe (maxima) formula instead of the diffraction-minima condition. |
| 14. Silvered Plano-Convex (2025 Jan, NVQ) | Plano-convex f=20 cm, plane surface silvered. New focal length? Answer: 10 cm. Solution: P=2P_L+P_M; P_M=0 (plane)→F=f/2=10. Trap: Forgetting the double pass (2P_L). |
| 15. Coherent Intensity (2023 Jan) | Two coherent sources intensity ratio 4:1. I_max/I_min? Answer: 9:1. Solution: a₁/a₂=2; (2+1)²/(2−1)²=9. Trap: Using the intensity ratio directly instead of amplitudes. |
| 🎯 These are 15 of the 200+ JEE Main Optics PYQs in the app. Drill all of them. | |
|---|---|
| Every question above — including the compulsory NVQ type — is inside Logic Bloom, mapped across all shifts. Trace rays through silvered lenses, set up YDSE fringe shifts, work critical angles and prism deviations. When a trap catches you, TarQ teaches the reasoning — not just the answer. Your Mistake Book tracks exactly which trap cost you — the sign-convention slip, the 2P_L+P_M error, the apparent-depth direction. Then take it into Battleground — 1v1 duels under real exam pressure. Get Logic Bloom — Free to start → |
How to Prepare Based on the Data
| 📌 Data-Driven Strategy for JEE Main Optics | |
|---|---|
| Burn in the sign convention first | It's the primary filter. Real object → negative u; real image in a mirror → negative v; "magnified real" → negative m. Everything downstream depends on it. |
| Master the silvered lens | P = 2P_L + P_M (double pass), relative μ when immersed, object at 2F_eq for autocollimation. The highest-frequency Ray archetype. |
| Drill the two YDSE staples | Coinciding maxima (n₁λ₁=n₂λ₂) and the slab shift (μ−1)t·D/d toward the covered slit. Together they're most of Wave Optics. |
| Do NOT study resolving power | Rayleigh's criterion for microscopes/telescopes is deleted. Polarisation (Malus, Brewster) is still active. |
| Keep the width formulae apart | Single-slit central max = 2λD/a; YDSE fringe = λD/d. The factor of 2 is a planted trap. |
| Trace it, don't plug it | Logic Bloom's Playground turns Optics into interactive ray-tracing — silvered lenses, spaced lenses, YDSE shifts — with TarQ teaching the reasoning. Drill every PYQ including NVQs, with your Mistake Book catching the sign and unit errors. Then test under pressure in Battleground. Free to start. |
Building your JEE Main Physics base? This is the single highest-weightage chapter in it.
| 🎯 Up to 3 questions per shift. Highest-weightage Physics chapter. Formula-driven, sign-sensitive, NVQ-heavy. The patterns are here. The practice is in the app. | |
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| 🎮 Playground Understand through practice — with TarQ |
Every Optics concept as interactive practice — trace rays through a silvered lens, move an object and watch the image flip real-to-virtual, slide a slab across a YDSE slit and see the fringes shift. Drill every PYQ across all shifts, including the NVQ type. When you're stuck, TarQ teaches the reasoning. Mistake Book catches the sign and silvered-lens slips before the exam does. Get the app → |
| ⚔️ Battleground Score through practice — 1v1 duels |
NVQ accuracy under time pressure is what this chapter rewards. Battleground trains exactly that — timed 1v1 duels across Physics, Chemistry, Biology, ELO climbing through 6 tiers. Get the app → |
| Understand through games. Score through practice. Get Logic Bloom — Free to start → |
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FAQs — Optics JEE Main PYQ
Q1: How many questions come from Optics in JEE Main?
Optics reliably delivers 2-3 questions per shift, worth up to 12 marks and 8-12% of the Physics section. Ray Optics is now the single highest-weightage individual chapter in JEE Main Physics — its question volume rose about 146% in 2025 — and Wave Optics adds a further 3-4%.
Q2: What is the silvered-lens formula for JEE Main?
For a lens silvered on one face, the equivalent power is P = 2P_L + P_M, because light passes through the lens twice and reflects off the mirror once. When the silvered lens is immersed in a liquid, the lens power P_L must be calculated using the relative refractive index (lens index divided by liquid index), not the air value. This double-counting and the relative-index correction are the two most common errors.
Q3: Is resolving power still in the JEE Main syllabus?
No. The resolving power of microscopes and telescopes (Rayleigh's criterion) was removed in the 2024 rationalisation and should not be studied. Basic telescope and microscope magnification formulas technically remain but appear very rarely. Polarisation, including Malus's law and Brewster's law, remains actively tested.
Q4: How does inserting a glass slab shift the YDSE fringe pattern?
Placing a slab of thickness t and refractive index μ in front of one slit adds an optical path of (μ−1)t, shifting the entire fringe pattern by Δy = (μ−1)t·D/d toward the slit that is covered. A common trap is getting the direction wrong or using μt instead of (μ−1)t for the extra path.
Q5: Are there actual JEE Main Optics PYQs to practice?
Yes — this article contains 15 representative JEE Main PYQs with worked solutions and traps explained, including Numerical Value type. For the full set of 200+ JEE Main Optics PYQs mapped across all shifts with TarQ teaching and a Mistake Book, download Logic Bloom. Free to start.