CBSE Class 10 Science Revision Notes Chapter 9 Light Reflection and Refraction 2026–27

Light makes objects visible when it reflects from them and reaches our eyes. In CBSE Class 10 Science Chapter 9, students study reflection, refraction, mirrors, lenses, formulas and ray diagrams.

Light – Reflection and Refraction explains how light behaves when it strikes a surface or passes from one transparent medium to another. Reflection forms images in mirrors, while refraction bends light at the boundary of two media.

Use these CBSE Class 10 Science Revision Notes Chapter 9 for the 2026–27 academic year to revise spherical mirrors, lenses, sign conventions, ray diagrams and numerical formulas. Focus on image formation tables, mirror formula, lens formula, refractive index and power of lens.

Key Takeaways

• Reflection: Light returns to the same medium after striking a polished surface.
• Spherical mirrors: Concave and convex mirrors form images based on object position.
• Refraction: Light bends when it passes obliquely from one transparent medium to another.
• Lens power: Power of a lens is the reciprocal of focal length in metres.

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CBSE Class 10 Science Revision Notes Chapter 9 on Light Reflection and Refraction: Chapter Overview

Light usually travels in straight lines. A ray of light represents the path along which light travels.

This chapter uses straight-line propagation of light. It explains image formation by mirrors and lenses through ray diagrams.

Important Topics in CBSE Notes Class 10 Science Chapter 9 Light Reflection and Refraction

Class 10 Science Chapter 9 Notes combine theory, formulas and ray diagrams. Image formation tables are central to this chapter.

Numericals in this chapter usually need the correct sign convention. Ray diagrams need correct positions of P, F, C, O, 2F1 and 2F2.

Light Reflection and Refraction Class 10 Notes: Reflection of Light

Reflection of light occurs when light falls on a surface and returns to the same medium. A highly polished surface reflects most of the light falling on it.

Laws of Reflection in Class 10 Science Chapter 9 Notes

The laws of reflection apply to plane mirrors and spherical mirrors.

Formula form:

Angle of incidence = Angle of reflection

i = r

Image Formed by a Plane Mirror

A plane mirror forms a virtual and erect image. The image is laterally inverted.

The image cannot be obtained on a screen because reflected rays only appear to meet behind the mirror.

Spherical Mirrors in CBSE Class 10 Science Revision Notes Chapter 9

Spherical mirrors have reflecting surfaces that form part of a sphere. They are of two types: concave mirror and convex mirror.

Concave and Convex Mirrors in Light Reflection Notes

A concave mirror can form real or virtual images. A convex mirror always forms a virtual, erect and diminished image.

Important Terms Related to Spherical Mirrors

For a concave mirror, C and F lie in front of the mirror. For a convex mirror, C and F lie behind the mirror.

Relation Between Radius of Curvature and Focal Length

For spherical mirrors of small aperture:

R = 2f

This means the principal focus lies midway between the pole and the centre of curvature.

Image Formation by Spherical Mirrors in Class 10 Science Chapter 9 Notes

Image formation depends on the position of the object. The main points used in mirror ray diagrams are P, F and C.

Image Formation by Concave Mirror

A concave mirror forms different images for different object positions.

When the object is between P and F, a concave mirror works like a shaving mirror. It forms an enlarged, virtual and erect image.

Image Formation by Convex Mirror

A convex mirror always gives a virtual and erect image. The image is always smaller than the object.

Convex mirrors give a wider field of view. This makes them useful in vehicles.

Uses of Concave and Convex Mirrors

Convex mirrors are preferred as rear-view mirrors because they show a larger area behind the vehicle.

Mirror Formula, Magnification and Sign Convention in Light Reflection Class 10 Notes

The New Cartesian Sign Convention is used for spherical mirrors. The pole of the mirror is taken as the origin.

Mirror formula:

1/v + 1/u = 1/f

Magnification by spherical mirror:

m = h'/h

m = -v/u

For a spherical mirror:

R = 2f

Refraction of Light in CBSE Notes Class 10 Science Chapter 9

Refraction is the change in direction of light when it passes obliquely from one transparent medium to another. It happens because the speed of light changes in different media.

A pencil partly dipped in water appears bent because of refraction. A coin in water appears raised for the same reason.

Laws of Refraction and Snell’s Law

Refraction follows two laws.

Snell’s law:

sin i/sin r = constant

This constant is called the refractive index of the second medium with respect to the first medium.

Rarer and Denser Medium in Refraction Notes

A medium with higher refractive index is optically denser. A medium with lower refractive index is optically rarer.

The speed of light is higher in an optically rarer medium. It is lower in an optically denser medium.

Refraction Through a Rectangular Glass Slab

A light ray bends twice when it passes through a rectangular glass slab. It bends at the air-glass surface and again at the glass-air surface.

The emergent ray is parallel to the incident ray. It is slightly shifted sideways due to lateral displacement.

Refractive Index in Light Reflection and Refraction Class 10 Notes

Refractive index tells how much a medium changes the speed of light. It can be written using speed of light in two media.

Speed of light in vacuum:

3 × 10⁸ m/s

If the refractive index of diamond is 2.42, it means light travels 2.42 times faster in air or vacuum than in diamond.

Spherical Lenses in CBSE Class 10 Science Revision Notes Chapter 9

A lens is a transparent material bounded by two surfaces. One or both surfaces are spherical.

Convex and Concave Lenses

A convex lens is also called a converging lens. A concave lens is also called a diverging lens.

A ray passing through the optical centre of a lens goes without deviation.

Image Formation by Convex Lens

A convex lens forms real or virtual images depending on object position.

A convex lens acts as a magnifying glass when the object is between the focus and optical centre.

Image Formation by Concave Lens

A concave lens always forms a virtual, erect and diminished image.

The image formed by a concave lens is always on the same side as the object.

Lens Formula, Magnification and Power of Lens in Class 10 Science Chapter 9 Notes

For lenses, all distances are measured from the optical centre. The focal length of a convex lens is positive, and the focal length of a concave lens is negative.

Lens formula:

1/v - 1/u = 1/f

Magnification by lens:

m = h'/h

m = v/u

Power of lens:

P = 1/f

Here, f is measured in metres.

The SI unit of power of lens is dioptre. It is written as D.

1 D = 1 m⁻¹

One dioptre is the power of a lens whose focal length is 1 metre.

Important Formulas in Light Reflection and Refraction Class 10 Notes

These formulas are important for Class 10 Physics Light Reflection and Refraction numericals.

Always convert focal length into metres before calculating power of lens.

Important Points of CBSE Class 10 Science Chapter 9 Light Reflection and Refraction

These quick notes cover the main facts from CBSE Notes Class 10 Science Chapter 9.

Useful Links for Class 10 Science