Ray Optics and Optical Instruments is Chapter 9 of Class 12 Physics and carries around 7 marks in the CBSE Boards exam every year. The important topics of this chapter are mirrors, lenses, total internal reflection, prisms, and optical instruments like microscopes and telescopes.
- This page contains the free PDF formula sheet on Ray Optics and Optical Instruments Class 12 with all 11 key formulas for quick revision.
- All the important formulas are provided below in a single PDF, which you can also take multiple printouts and fix in your study room.
- Regular revision of derivations such as the magnification formula, sign convention, etc will be helpful during exam time.
- 11 formulas with SI units - from mirror formula to telescope magnification.
- CBSE, JEE Main, and NEET coverage with topic-wise weightage breakdown.
- Single-page PDF card for a fast night-before revision pass.
Ray Optics and Optical Instruments - Class 12 Physics Formula Reference Table
The 11 formulas below cover every numerical in Chapter 9. Each row gives the concept, the formula, and the SI unit. Students preparing for CBSE Boards need rows 1 to 9; JEE Main students need the full table plus the lens-combination extension.
| Concept | Formula | SI Unit |
|---|---|---|
| Mirror formula | 1/v + 1/u = 1/f | n/a |
| Snell's law | n1 sinθ1 = n2 sinθ2 | n/a |
| Critical angle | sinθc = n2 / n1 | n/a |
| Refraction at spherical surface | n2/v - n1/u = (n2 - n1)/R | n/a |
| Lens formula | 1/v - 1/u = 1/f | n/a |
| Lens-maker's formula | 1/f = (n - 1)(1/R1 - 1/R2) | n/a |
| Power of lens | P = 1/f (f in m) | diopter |
| Lenses in contact | 1/F = ∑ 1/fi | n/a |
| Prism formula | n = sin((A+Dm)/2) / sin(A/2) | n/a |
| Compound microscope magnification | M = (L/fo)(1 + D/fe) | n/a |
| Telescope magnification | M = fo / fe | n/a |
Lens-maker's formula - focal length from geometry and refractive index.
Chapter 9 Ray Optics and Optical Instruments - Topic-by-Topic Formula Breakdown
Chapter 9 splits into 6 sub-topics. Each sub-topic has its own formulas and a distinct mark allocation in CBSE and JEE Main.
- Reflection at plane and spherical mirrors: mirror formula 1/v + 1/u = 1/f (2 marks in CBSE)
- Refraction and Snell's law: n1 sinθ1 = n2 sinθ2 (2 marks)
- Total internal reflection: critical angle formula, optical fibres (3 marks)
- Refraction at spherical surfaces and lens-maker's formula: 5-mark derivation in CBSE
- Prism and dispersion: minimum deviation formula, dispersive power (3 marks)
- Optical instruments: compound microscope and telescope magnification formulas (5 marks)
Class 12 Physics Chapter 9 Weightage Compared to Other Chapters
The table below shows average CBSE marks per chapter over the last five papers. Chapter 9 is one of the highest-scoring chapters in Class 12 Physics.
| Chapter | Topic | Avg CBSE Marks |
|---|---|---|
| Ch 1 | Electric Charges and Fields | 6 marks |
| Ch 2 | Electrostatic Potential and Capacitance | 7 marks |
| Ch 3 | Current Electricity | 7 marks |
| Ch 4 | Moving Charges and Magnetism | 6 marks |
| Ch 5 | Magnetism and Matter | 3 marks |
| Ch 6 | Electromagnetic Induction | 5 marks |
| Ch 7 | Alternating Current | 6 marks |
| Ch 8 | Electromagnetic Waves | 2 marks |
| Ch 9 | Ray Optics and Optical Instruments | 7 marks |
| Ch 10 | Wave Optics | 5 marks |
| Ch 11 | Dual Nature of Radiation and Matter | 4 marks |
| Ch 12 | Atoms | 3 marks |
| Ch 13 | Nuclei | 3 marks |
| Ch 14 | Semiconductor Electronics | 6 marks |
Ray Optics and Optical Instruments Previous Year Questions (2021-2026)
The table below maps every CBSE Board, JEE Main, and NEET appearance of Chapter 9 topics over the last six sessions.
| Year | CBSE Board | JEE Main | NEET |
|---|---|---|---|
| 2026 | Lens-maker's formula derivation (5 marks) | Prism minimum deviation (4 marks) | Lens and mirror formula, optical instruments (2 questions) |
| 2025 | Compound microscope magnification (5 marks) | Total internal reflection critical angle | Mirror formula numerical |
| 2024 | Astronomical telescope derivation (5 marks) | Lens combination focal length | Snell's law MCQ |
| 2023 | Refraction at spherical surface (3 marks) | Prism dispersion problem | Defects of vision (myopia) |
| 2022 | Total internal reflection in optical fibre (3 marks) | Telescope magnification | Concave mirror image |
| 2021 | - | Lens-maker's formula numerical | Convex lens magnification |
Common Mistakes in Ray Optics and Optical Instruments Numericals
Mistake 1: Substituting values before simplifying the formula. Always rearrange to isolate the unknown first.
Mistake 2: Ignoring sign convention. Use the standard convention consistently - incident light travels left to right and distances are measured from the pole of the mirror or lens.
Mistake 3: Getting the critical angle formula wrong. In sinθc = n2/n1, the value n1 must be the denser medium. Swapping them gives a completely wrong angle.
Mistake 4: Mixing up the signs of R1 and R2 in the lens-maker's formula. Check the geometry: is the centre of curvature on the same side as the outgoing ray or the incoming ray?
Each mistake typically costs 1 to 2 marks in CBSE.
Sign convention - the most common source of errors in ray optics numericals.
Ray Optics and Optical Instruments Class 12 Physics - Video Lecture
Source: JEE Physics By Vedantu on YouTube
Student Feedback
In a Collegedunia poll of 15,410 Class 12 Physics students before the 2026 boards, 74% of students rated the formula sheet as their most-used revision resource, ahead of full chapter notes and solved-example PDFs.
- 74% of students placed the formula sheet at the top of their revision list.
- 58% reviewed the formula sheet daily in the last 7 days before the boards.
- 4 out of 5 students keep a printed copy in their notebook.
- Average revision time: 12 minutes per chapter for a focused pass.
Source: 2025-26 Class 12 Physics student poll. Sample of 15,410 students from CBSE schools across 16 states.
Other Resources for Class 12 Ray Optics and Optical Instruments
| Resource Type | Link |
|---|---|
| NCERT Notes | Class 12 Ray Optics Notes |
| NCERT Solutions | Class 12 Ray Optics NCERT Solutions |
| NCERT Book PDF | Class 12 Ray Optics NCERT Book PDF |
| Exemplar Book PDF | Class 12 Ray Optics NCERT Exemplar Book PDF |
| Exemplar Solutions | Class 12 Ray Optics NCERT Exemplar Solutions |
| Handwritten Notes | Class 12 Ray Optics Handwritten Notes |
| Formula Sheet | Ray Optics and Optical Instruments Formula Sheet |
NCERT Formula Sheets for Class 12 Physics - All Chapters
| Chapter | Resource |
|---|---|
| Chapter 1 | Electric Charges and Fields Formula Sheet |
| Chapter 2 | Electrostatic Potential and Capacitance Formula Sheet |
| Chapter 3 | Current Electricity Formula Sheet |
| Chapter 4 | Moving Charges and Magnetism Formula Sheet |
| Chapter 5 | Magnetism and Matter Formula Sheet |
| Chapter 6 | Electromagnetic Induction Formula Sheet |
| Chapter 7 | Alternating Current Formula Sheet |
| Chapter 8 | Electromagnetic Waves Formula Sheet |
| Chapter 9 | Ray Optics and Optical Instruments Formula Sheet |
| Chapter 10 | Wave Optics Formula Sheet |
| Chapter 11 | Dual Nature of Radiation and Matter Formula Sheet |
| Chapter 12 | Atoms Formula Sheet |
| Chapter 13 | Nuclei Formula Sheet |
| Chapter 14 | Semiconductor Electronics Formula Sheet |
Class 12 Physics Chapter 9 Ray Optics and Optical Instruments Formula Sheet FAQs
Ques. How many formulas are in the Class 12 Chapter 9 Physics formula sheet?
Ans. 11 formulas cover every numerical in Chapter 9. The Quick-Reference Table above lists them all with SI units. The PDF has the same list on a single A4 sheet for night-before revision.
Ques. What is the weightage of Class 12 Physics Chapter 9?
Ans. Chapter 9 carries 7 marks in CBSE Class 12 Physics, around 4 to 5 percent in JEE Main, and 2 to 3 questions per year in NEET. The formula sheet covers all formulas needed for every variant.
Ques. Where can I download the Chapter 9 Physics formula sheet PDF?
Ans. The PDF is available directly on this page via the flipbook above. Click the download button to get the PDF with all 11 formulas plus JEE and NEET extensions.
Ques. Are the JEE Main extensions covered in this formula sheet?
Ans. Yes. The formula sheet includes 2 to 3 derived results that JEE Main and JEE Advanced test but CBSE Boards rarely ask. These are flagged with a distinct marker in the PDF.
Ques. What is the most-tested formula in Ray Optics and Optical Instruments?
Ans. The lens-maker's formula and the telescope magnification formula appear most often in 5-mark CBSE derivations and JEE Main numericals. The mirror formula is the most common in 2-mark MCQs.
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