Class 10 Science Chapter 9 Light – Reflection and Refraction

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Class 10 → Science → Chapter 9: Light – Reflection and Refraction

I. Chapter Summary

Light is a form of energy that enables us to see objects. This chapter explains how light behaves when it strikes surfaces or travels through different media. It covers the laws of reflection, types of mirrors (plane, concave, convex), image formation, and uses of mirrors. It also explains refraction, refractive index, and image formation through lenses (convex and concave). Applications like the human eye and optical instruments are also discussed.

II. Key Concepts Covered

1. Reflection of Light

  • Bouncing back of light when it strikes a surface.
  • Laws of Reflection:
    • Angle of incidence = Angle of reflection
    • Incident ray, reflected ray, and normal lie in the same plane

2. Spherical Mirrors

  • Concave Mirror: Converges light (used in headlights, shaving mirrors)
  • Convex Mirror: Diverges light (used in rear-view mirrors)

3. Image Formation by Mirrors

  • Real & inverted / Virtual & erect images depending on object position

4. Mirror Formula & Magnification

  • Relation between object distance (u), image distance (v), focal length (f)

5. Refraction of Light

  • Bending of light when it passes from one medium to another

6. Refractive Index

  • Measure of bending of light in a medium

7. Lenses

  • Convex Lens: Converging
  • Concave Lens: Diverging

8. Power of Lens

  • Ability of lens to converge/diverge light

9. Human Eye

  • Structure and functioning
  • Defects: Myopia, Hypermetropia, Presbyopia

III. Important Questions

(A) MCQs (1 Mark)

  1. The image formed by a plane mirror is:
    (a) Real
    (b) Virtual
    (c) Inverted
    (d) Diminished
    Answer: (b) Virtual
  2. The SI unit of power of a lens is:
    (a) Watt
    (b) Joule
    (c) Dioptre
    (d) Newton
    Answer: (c) Dioptre
  3. A concave mirror produces a real image when the object is:
    (a) Between pole and focus
    (b) At focus
    (c) Beyond focus
    (d) At infinity
    Answer: (c) Beyond focus
  4. Refractive index depends on:
    (a) Density
    (b) Temperature
    (c) Nature of medium
    (d) All of these
    Answer: (d) All of these

(B) Short Answer Questions (2/3 Marks)

  1. State the laws of reflection. (PYQ 2020)
  2. Define refractive index and write its formula. (PYQ 2019)
  3. Differentiate between concave and convex mirrors.
  4. What is power of a lens? Write its unit. (PYQ 2018)

(C) Long Answer Questions (5 Marks)

  1. Draw ray diagrams for image formation by a concave mirror. (PYQ 2020)
  2. Explain refraction with laws and diagram. (PYQ 2019)
  3. Describe image formation by convex lens with diagrams. (PYQ 2022)
  4. Explain defects of vision and their correction. (PYQ 2023)

(D) HOTS Questions

  1. Why do objects appear bent in water? Explain scientifically.
  2. Why are convex mirrors used as rear-view mirrors in vehicles?

IV. Key Formulas/Concepts

  • Mirror Formula:

$frac{1}{f} = frac{1}{v} + frac{1}{u}$​

  • Magnification (Mirror):

$m = frac{h_i}{h_o} = frac{v}{u}$​

  • Refractive Index:

$n = frac{c}{v}$​

  • Lens Formula:

$frac{1}{f} = frac{1}{v} – frac{1}{u}$​

  • Power of Lens:

$P = frac{1}{f , (text{in meters})}$​

V. Deleted Portions (CBSE 2025–2026)

  • Detailed study of ray diagrams for spherical mirrors (some cases reduced)
  • Numericals on refraction through glass slab (reduced weightage)

(Refer to NCERT official rationalization for exact updates.)

VI. Chapter-Wise Marks Bifurcation (Estimated – CBSE 2025–2026)

Unit/Chapter Estimated Marks Type of Questions Typically Asked
Light – Reflection & Refraction 10–12 Marks MCQs, Numericals, Ray Diagrams, Conceptual Questions

Note: This is an estimate. Actual marks may vary.

VII. Previous Year Questions (PYQs)

1 Mark

  • Define focal length. (CBSE 2019)

2/3 Marks

  • State laws of refraction. (CBSE 2020)
  • What is magnification? (CBSE 2018)

5 Marks

  • Draw ray diagram for convex lens. (CBSE 2022)
  • Explain defects of vision. (CBSE 2023)

VIII. Real-World Application Examples

  • Rear-view mirrors in vehicles → convex mirrors
  • Cameras → convex lenses
  • Spectacles → correction of vision defects
  • Solar cookers → concave mirrors
  • Optical fibres → refraction principle

IX. Student Tips & Strategies for Success

Time Management

  • Allocate time daily for numericals + diagrams
  • Practice ray diagrams regularly

Exam Preparation

  • Learn formulas and sign conventions
  • Solve previous year questions

Stress Management

  • Take short breaks
  • Revise regularly instead of last-minute study

X. Career Guidance & Exploration (Class 10)

Streams After Class 10

  • Science: Engineering, Medical, Research
  • Commerce: Business, CA, Finance
  • Arts: Humanities, Law, Civil Services

Entrance Exams (Basic Awareness)

  • JEE Main
  • NEET
  • CUET

XI. Important Notes

  • Always follow the latest syllabus from CBSE
  • Practice diagrams and numericals regularly
  • Focus on understanding concepts, not memorization
  • Revise formulas weekly

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