CBSE · Class 10 · Science · Chapter 9
Light - Reflection and Refraction — Class 10 Science (CBSE) explained
- Board exam 2026-27
- 4 lessons
- 32 scenes
- About 24 min
- Updated
Quick answer
Light - Reflection and Refraction is Chapter 9 of CBSE Class 10 Science. It covers visibility and rays, spherical mirror geometry, convex mirror images and uses, refraction observations, absolute index and optical density and lens foci and focal length. AI Lessons teaches it in 4 narrated lessons (about 24 minutes) with an AI tutor and board-pattern practice.
What you’ll learn
Lesson 1: Reflection and Concave Mirrors
6 min- Why Objects Become Visible
- Reflection Laws and Plane Mirror Images
- Name the Parts of a Spherical Mirror
- Principal Focus, Focal Length and Aperture
- How Object Position Changes a Concave Mirror Image
- Two Mirror Rays Connected with the Focus
- Rays Through the Centre and at the Pole
- Construct Concave Mirror Images and Explain Their Uses
Lesson 2: Mirror Calculations and the Start of Refraction
6 min- Why Convex Mirrors Are Used for Rear View
- The New Cartesian Sign Convention
- Mirror Formula and Magnification
- Worked Example: A Bus in a Convex Mirror
- Worked Example: Where to Place the Screen
- Why a Pencil Appears Displaced in Water
- Refraction Through a Rectangular Glass Slab
- The Laws of Refraction
Lesson 3: Refractive Index and Lens Images
6 min- Refractive Index Compares Light Speeds
- Absolute Refractive Index and Optical Density
- Convex and Concave Lenses
- A Lens Has Two Principal Foci
- Read the Convex Lens Image Pattern
- The Consistent Image Pattern of a Concave Lens
- Three Rays for Lens Diagrams
- Build Lens Images from Two Rays
Lesson 4: Lens Calculations, Power and Practice
6 min- Sign Convention for Spherical Lenses
- Lens Formula and Magnification
- Worked Example: Find the Concave Lens Object Distance
- Worked Example: A Real Image from a Convex Lens
- Power Measures Convergence or Divergence
- Read the Sign of a Lens Prescription
- Add Powers for Lenses in ContactNot assessed
- Recap: Trace, Calculate, Interpret and Practise
Key concepts
- Visibility and rays
- The sharp shadow cast by an opaque object suggests that light travels in straight lines.
- Spherical mirror geometry
- The radius of that sphere is the radius of curvature. The straight line through the pole and centre of curvature is the principal axis.
- Convex mirror images and uses
- Convex mirrors are preferred for vehicle rear view because they give erect images and a wider field of view.
- Refraction observations
- The change in direction when light travels obliquely from one transparent medium to another is called refraction.
- Absolute index and optical density
- A larger refractive index means an optically denser medium.
- Lens foci and focal length
- Focal length is the distance from the optical centre to a principal focus.
- Lens formula and magnification
- The lens formula is general and valid for spherical lenses.
- Power of a lens
- Power is the reciprocal of focal length.
Exam focus
- Board exam
- CBSE assesses this chapter in the 2026-27 year-end board examination.
- Syllabus
- Reflection of light by curved surfaces; Images formed by spherical mirrors, centre of curvature, principal axis, principal focus, focal length, mirror formula (Derivation not required), magnification. Refraction; Laws of refraction, refractive index. Refraction of light by spherical lens; Image formed by spherical lenses; Lens formula (Derivation not required); Magnification. Power of a lens.
- Not assessed
- These parts go beyond the 2026-27 syllabus and are taught for understanding only: Add Powers for Lenses in Contact.
- Exam note
- Mirror and lens formula derivations are not required.
- Paper pattern
- 80 marks, 3 hours, 39 questions in three sections (A Biology, B Chemistry, C Physics); internal assessment 20. Units: I Chemical Substances 25, II World of Living 25, III Natural Phenomena 12, IV Effects of Current 13, V Natural Resources 5.
- Question style
- About 50% of board questions are competency-focused: case-based, source-based, integrated, data interpretation, situational and application-oriented.
- Practice in the app
- 114 board-pattern questions with marking schemes: 34 multiple choice (1 mark), 15 assertion–reason (1 mark), 25 very short answer (2 marks), 23 short answer (3 marks), 4 long answer (5 marks) and 13 case-based (4 marks).
Sample questions with marking points
Board-pattern questions from the AI Lessons practice set for this chapter. The marking points show what an examiner looks for; full model answers are in the app.
Very short answer2 marks
A vehicle designer chooses a convex mirror instead of a plane mirror for rear view. Give two reasons that justify this choice.
Marking points
- Always forms an erect, diminished image.1
- Provides a wider field of view, allowing a larger area of traffic to be seen.1
Short answer3 marks
An assistant labels a lens of power – 2.5 D as 'convex, focal length + 0.40 m'. Identify and correct both errors. Show the calculation used to check the focal length.
Marking points
- Corrects the lens type to concave.0.5
- Explains that negative power identifies a concave lens.0.5
- Uses P = 1/f, with focal length in metres.1
- Obtains f = – 0.40 m and corrects the positive sign on the label.1
Frequently asked questions
What does Light - Reflection and Refraction cover in Class 10 Science?
It covers visibility and rays, spherical mirror geometry, convex mirror images and uses, refraction observations, absolute index and optical density and lens foci and focal length. AI Lessons teaches it in 4 lessons: Reflection and Concave Mirrors, Mirror Calculations and the Start of Refraction, Refractive Index and Lens Images and Lens Calculations, Power and Practice.
Is Light - Reflection and Refraction in the CBSE Class 10 board exam?
Yes. CBSE assesses Light - Reflection and Refraction in the 2026-27 year-end board examination. 1 short part goes beyond the syllabus and is marked as not assessed.
Why does a ray passing through C of a concave mirror return along the same path after reflection?
It falls along the normal to the reflecting surface. A ray through C is incident along the normal to the spherical reflecting surface and therefore retraces its path.
What is the principal axis?
The principal axis is the horizontal coordinate axis.
What is refraction?
The change in direction when light travels obliquely from one transparent medium to another is called refraction.
What is a lens?
A lens is a transparent material bounded by two surfaces, with at least one spherical surface. A double convex lens bulges outwards on both sides.
To calculate lens power in dioptres, which combination of formula and focal-length unit must be used?
P = 1/f, with f in metres. Power is the reciprocal of focal length, and focal length must be expressed in metres to obtain dioptres.
How does AI Lessons teach Light - Reflection and Refraction?
As 4 narrated, animated lessons (32 scenes, about 24 minutes in all), with an AI tutor that knows the step you are on and board-pattern practice with marking schemes. The full lessons open after sign-in on an AI Lessons account.
Watch the full lesson
Light - Reflection and Refraction, as a narrated, animated lesson
4 lessons · 32 animated scenes · about 24 minutes, with an AI tutor that knows the step you are on and 114 board-pattern questions with marking schemes.
Lessons open after sign-in. A parent or guardian holds the account and adds each child.