CBSE Notes Class 10 Science Chapter 9 - Light: Reflection and Refraction

CBSE Notes Class 10 Science Chapter 9 – Light: Reflection and Refraction introduces students to the fundamental behavior of light and its interaction with mirrors and lenses. This CBSE Class 10 Science Notes chapter explains core concepts such as the laws of reflection, spherical mirrors, refraction of light, refractive index, image formation, and ray diagrams—topics that frequently appear in board exams and competitive tests. A strong grasp of these principles helps students understand everyday optical phenomena and strengthens problem-solving skills in physics.

These CBSE Light Class 10 notes are structured to present concepts in a clear, exam-oriented manner with concise explanations, formulas, and diagram-based learning. The content is strictly aligned with NCERT, helping learners master light reflection and refraction class 10 notes efficiently while improving accuracy in diagram-based and application-based questions in the CBSE Class 10 examination.

1.0Download CBSE Notes for Class 10 Science Chapter 9: Light:Reflection and Refraction - Free PDF!!

Download CBSE Notes for Class 10 Science Chapter 9: Light – Reflection and Refraction (Free PDF) to master ray diagrams, mirror and lens formulas, magnification, and numerical problems. These syllabus-aligned notes support quick revision and effective board exam preparation.

2.0Reflection of Light

Reflection is the process where light rays encounter the boundary between two different media and bounce back into the original medium. Specifically, it refers to the phenomenon where light rays that strike the surface of an object are returned into the same medium rather than passing through or being absorbed.

3.0Laws of Reflection

1. The path of the incoming ray, the path of the reflected ray, and the perpendicular line (normal) to the surface at the point of incidence are all situated in the same plane.
2. The angle at which the incoming light ray impacts a surface (the angle of incidence) is equal to the angle at which it bounces off (the angle of reflection) ∠i=∠r

4.0Some Basic Terms Related To Spherical Mirrors

5.0Sign Conventions For Spherical Mirrors

6.0Image Formation By Convex And Concave Mirror

Convex Mirror

Concave Mirror

Uses of Concave and Convex Mirror

1. Concave Mirror-Reflectors in the headlights, search light in torches
2. Convex Mirror-Rear View in an Automobile.

7.0Mirror Formula

The relationship between the object distance(u), the image distance(v) and the focal length(f) is given by Mirror Formula.

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

8.0Magnification

• The ratio of height image $(h_2)$ to the height of object $(h_1)$ is called magnification or linear magnification. $m=\frac{h_2}{h_1}$
• Magnification is also related to object distance and image distance. $m=\frac{h_2}{h_1}=-\frac{v}{u}$
• Magnification also expressed as $m=\frac{f}{f-u}=\frac{f-v}{f}$

9.0Refraction of Light

The phenomenon of change in path of light when it passes from one medium to another is called Refraction.

Cause of Refraction

The bending of light takes place when it passes from one medium to another because speed of light changes from one medium to another.Speed of light is different in different media.

Laws of Refraction

1. The incident ray, the refracted ray, and the normal at the point of incidence are all contained within a single plane.
2. $\frac{Sini}{Sinr}=Constant(\mu )$

Refraction From Rarer to Denser Medium and Denser to Rarer Medium Ray Diagram

Refraction Through A Rectangular Glass Slab

When light passes through a rectangular glass slab, it undergoes refraction at both the entry and exit faces:

1. Entry Refraction: As light enters the glass from air, it bends towards the normal due to the slower speed of light in the denser glass.
2. Inside the Slab: The light travels in a straight line within the slab, still refracted but at an angle to the normal.
3. Exit Refraction: Upon leaving the slab, the light bends away from the normal as it moves back into the less dense air.

Key Points

• Parallel Faces: The entry and exit rays are parallel because the angle of incidence equals the angle of emergence.
• Lateral Displacement: Although parallel, the light is displaced sideways from its original path, depending on the slab's thickness, the angle of incidence, and the glass's refractive index.

In essence, while the light rays remain parallel, they shift from their initial path due to refraction.

10.0Refractive Index

Refractive index of a medium$(n_{21})$

The relative refractive index of a medium 2 w.r.t medium 1 is the ratio of speed of light in medium 1 to the speed of light in medium 2.

$n_{21}=\frac{\text{speed of light in medium 1}}{\text{speed of light in medium 2}}$

$n_{21}=\frac{v_1}{v_2}$

Absolute Refractive Index of a Medium

The proportion of speed of light in vacuum to the speed of light in a material is called absolute refractive index of medium.

$n=\frac{c}{v}=\frac{\text{speed of light in vacuum}}{\text{speed of light in medium}}$

• Optically denser-Greater the value of n less will be the speed of light.
• Optically rarer-Lesser the value of n greater will be the speed of light

11.0Image Formation In Spherical Lenses

(A). Rules to obtain images in Convex lens

• A ray parallel to the principal axis moves through the focal point after refraction.
•  A ray passing through the focal point emerges parallel to the principal axis.
•  A ray through the optical center continues straight without deviation.

(B). Rules to obtain images in Concave lens

•  A ray passes  parallel to the principal axis diverges as if it were coming from the focal point on the same side of the lens.
•  A ray directed towards the focal point diverges parallel to the principal axis.
•  A ray through the optical center continues straight without deviation.

For Convex Lens

For Concave Lens

1. Image Formation By Convex Lens

2. Image Formation By Concave Lens

12.0Sign Convention For Spherical Lenses

13.0Lens Formula And Magnification

• The relationship between object distance(u) ,image distance(v) and the focal length(f) is given by $\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
• Magnification-The ratio of height of image $(h_2)$ to the height of object $(h_1)$

$m=\frac{h_2}{h_1}=+\frac{v}{u}$

$m=\frac{f}{f+u}=\frac{f-v}{f}$

14.0Power of Lens

• It is the extent of convergence or divergence of light rays. Falling on it.A lens of short focal length bends the light rays more through large angles.
• The power of a lens is defined as the inverse of its focal length. $P=\frac{1}{F}$
• Units is Dioptre (D)
• For convex lens power is positive and for concave lens power is negative.

15.0Detailed CBSE Class 10 Science Chapter 9 – Key Notes

Light

Light is a form of energy which excites our sense of sight.

Speed of light in vacuum: 3 x10⁸ m/s.

Properties Of Light

Light consists of electromagnetic waves

Light travels in a straight line

Reflection of light

The process of sending back of light rays which fall on the surface of an object is called reflection of light.

Laws of Reflection

First law: The incident ray, the reflected ray and the normal at the point of incidence, all lie in the same plane.

Second law: The angle of incidence is equal to the angle of reflection.

i = r

Image Formation By a Plane Mirror

Properties Of Image Formed By a Plane Mirror

1. The image is virtual and erect. The size of image is exactly equal to the size of object.
2. The distance of image from mirror is equal to distance of object from mirror.
3. The image is laterally inverted

Spherical Mirrors

Concave mirror (Converging mirror)

Convex mirror (Diverging mirror)

Image Formation By a Concave Mirror

Ray Diagram	Position of the object	Position of the Image	Size of the Image	Nature of the Image
	At infinity	At focus F	Highly diminished, point sized	Real and inverted
	Between infinity and C	Between F and C	Diminished	Real and inverted
	At C	At C	Same size	Real and inverted
	Between C and F	Beyond C	Enlarged	Real and inverted
	At F	At infinity	Highly enlarged	Real and inverted
	Between P and F	Behind the mirror	Enlarged	Virtual and erect

Image Formation By a Convex Mirror

Ray Diagram	Position of the object	Position of the Image	Size of the Image	Nature of the Image
	At infinity	At the focus F, behind the mirror	Highly diminished, point sized	Virtual and erect
	Between infinity and the pole	Between P and F behind the mirror	Diminished	Virtual and erect

Uses Of Curved Mirrors

Relation between radius of curvature and focus

f = R/2

Mirror Formula

1/f = 1/v + 1/u

Magnification (m)

m = h₂/h₁ = -v/u

Optics : Refraction of Light

You might have observed that a lemon kept in water in a glass tumbler appears to be bigger than its actual size, when viewed from the sides. All these dayto-day experiences are based on a phenomenon called ‘refraction’.

Principle of least time

We all know that light ordinarily travels in straight lines. In going from one place to another, light will take the most efficient path and travel in a straight line.

This idea, which was formulated by the French scientist Pierre Fermat in about 1650, is called Fermat's principle of least time.

Refraction of light

The phenomenon of change in path of light when it passes from one medium to another is called 'refraction'.

Optically rarer medium

A transparent medium in which the speed of light is more is called 'optically rarer medium' (or simply 'rarer medium').

Optically denser medium

A transparent medium in which the speed of light is less is called 'optically denser medium' (or simply 'denser medium').

Cause of Refraction

The bending of light takes place when it passes from one medium to another because speed of light changes from one medium to another. Speed of light is different in different media.

What does not change during refraction of light?

The frequency of light does not change during the refraction of light. The speed and wavelength of light change during refraction of light.

v₁/v₂ = λ₁/λ₂

Refraction Through Rarer to Denser and dener to Rarer

Laws of refraction

The incident ray, the normal to the refracting surface at the point of incidence and the refracted ray, all lie in the same plane.

Laws of refraction

The ratio of sine of angle of incidence to the sine of angle of refraction is constant for two given media.

sin i/sin r = constant = n₂₁ (Snell's Law)

n₂₁ = Refractive index of medium 2 with respect medium 1

Angle of deviation (δ)

The angle through which the incident ray of light is deviated from its original path when it is refracted while passing from one transparent medium to another is called 'angle of deviation'

Relative refractive index of a medium (n₂₁)

The relative refractive index of a medium 2 with respect to medium 1 is the ratio of speed of light in medium 1 to the speed of light in medium 2.

n₂₁ = speed of light in medium 1/speed of light in medium 2

or

n₂₁ = V₁/V₂

Absolute refractive index of a medium

The ratio of speed of light in vacuum to the speed of light in a medium is called absolute refractive index of medium.

Refraction Through A Glass Slab

Incident Ray Is Parallel To The Emergent Ray But The Incident Ray Is Laterally Displaced.

Apparent depth

When an object lying inside an optically denser medium is seen from a rarer medium, its depth appears to be less than its real depth. This depth is called 'apparent depth'.

Ex. Fish In The Aquarium

n₁₂ = Real depth/Apparent depth

Image Formation By A Convex Lens

	Position of the object	Position of the Image	Size of the Image	Nature of the Image
	At infinity	Zero	Highly diminished, point sized	Real & inverted
	Beyond 2F₁	Between F and 2F	Diminished	Real & inverted
	At 2F₁	At 2F₂	Same size	Real & inverted
	Between F₁ and 2F₁	Beyond 2F₂	Enlarged	Real & inverted
	At F	At infinity	Highly enlarged	Real & inverted
	Between O and F₁	At infinity	Enlarged	Virtual & erect

Image Formation By Concave Lens

	Position of the Image	Position of the Image	Size of the Image	Nature of the Image
	At infinity	At focus F	Highly diminished, point sized	Virtual and erect
	Between ∞ and O	Between O and F same side as the object	Diminished	Virtual and erect

Uses of Lens

In all the optical instruments like, magnifying glass, microscope, binoculars, telescope, cameras, overhead projectors.

Convex lens: In magnifying glass, In spectacles

Concave lens: In door lenses, for correction of vision.

Lens Formula

The relationship between object distance (u), the image distance (v) and the focal length (f) is given by lens formula.

1/f = 1/v - 1/u

The distance of the object from optical centre of the lens is called the object distance (u).

The distance of the image from optical centre of the lens is called the image distance (v).

Magnification (m)

The ratio of height of image (h₂) to the height of object (h₁) is called magnification or linear magnification.

m = h₂/h₁

The magnification (m) is also related to the object distance (u) and image distance (v).

m = h₂/h₁ = -v/u

Power of lens

Reciprocal of its focal length.

P = 1/f

Unit of power of lens = Diopter (D)

1 diopter = 1 m⁻¹

Power of convex lens (converging lens) is 'positive'

Power of concave lens (diverging lens) is 'negative'.

16.0Benefits of CBSE Notes for Class 10 Science Chapter 9 - Light: Reflection and Refraction

• Problem-Solving Skills: Many notes include solved examples or highlight key steps for tackling numerical problems related to image formation, focal length, and magnification.
• Identification of Important Topics: Effective CBSE Notes often emphasise topics that are frequently tested or are crucial for building a strong foundation in optics.
• Personalised Learning: If you create your own notes, the process itself reinforces learning and allows you to tailor the information to your individual learning style and areas of difficulty.
• Reduced Exam Stress: Having organised notes can contribute to a feeling of preparedness and control, ultimately reducing anxiety before exams.

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