Light Reflection and Refraction Class 10 Notes

Light Reflection and Refraction Class 10 Notes explain how light behaves when it strikes a surface or passes from one medium to another. This chapter covers reflection, refraction, spherical mirrors, lenses, ray diagrams, mirror formula, lens formula, refractive index, magnification, power of a lens, sign convention, numericals, MCQs and important questions.

This chapter is commonly searched as Class 10 Science Chapter 9 Notes, Light Class 10 Notes, and Light Reflection Refraction Class 10 Notes. Chapter numbering may vary slightly depending on textbook edition, but the core concepts remain important for CBSE Class 10 Science board exam preparation.

Light Reflection and Refraction Class 10 Chapter Overview

Light is a form of energy that helps us see objects. We see objects because light from them enters our eyes. In this chapter, students learn how light travels, how it reflects from mirrors, how it refracts through glass and water, and how spherical mirrors and lenses form images.

Light Reflection and Refraction Class 10 Notes PDF Download

Students can download the Light Reflection and Refraction Class 10 Notes PDF to revise the chapter anytime, even without internet access. This PDF is designed for quick concept revision, formula practice, ray diagram preparation, and step-by-step numerical solving.

The notes cover important topics such as laws of reflection, spherical mirrors, mirror formula, refraction of light, Snell’s law, refractive index, spherical lenses, lens formula, power of lens, ray diagrams, MCQs, and important questions.

Download PDF: Light Reflection and Refraction Class 10 Notes PDF

What is Light?

Light is a form of energy that produces the sensation of vision. It travels in a straight line in a transparent medium. This straight-line path of light is called rectilinear propagation of light.

Important Properties of Light

Reflection of Light Class 10

Reflection of light is the bouncing back of light into the same medium after striking a surface. For example, when light falls on a plane mirror, it returns to the same medium and forms an image. This is reflection.

Reflection of Light Definition Class 10

Reflection of light is the phenomenon in which light rays bounce back into the same medium after striking a reflecting surface.

Important Terms in Reflection

Laws of Reflection Class 10

The laws of reflection are used to describe how light reflects from a surface.

First Law of Reflection

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

Second Law of Reflection

The angle of incidence is equal to the angle of reflection.

∠i = ∠r

Example

If a light ray falls on a mirror at an angle of incidence of 40°, then the angle of reflection will also be 40°.

Regular vs Diffuse Reflection

Important Note

Diffuse reflection does not mean that the laws of reflection fail. Each ray still follows the laws of reflection, but because the surface is uneven, reflected rays scatter in different directions.

Plane Mirror Class 10

A plane mirror is a flat reflecting surface. It forms an image that appears behind the mirror.

Image Formed by Plane Mirror

What is Lateral Inversion?

Lateral inversion means the left side of the object appears as the right side in the image, and the right side appears as the left side.

Example: The word “AMBULANCE” is written in reverse on ambulances so that drivers can read it correctly in rear-view mirrors.

Spherical Mirrors Class 10

A spherical mirror is a mirror whose reflecting surface is part of a hollow sphere. Spherical mirrors are of two types:

1. Concave mirror
2. Convex mirror

Concave Mirror Class 10

A concave mirror is a spherical mirror whose reflecting surface is curved inward. It is also called a converging mirror because it converges parallel rays of light.

Uses of Concave Mirror Class 10

Convex Mirror Class 10

A convex mirror is a spherical mirror whose reflecting surface is curved outward. It is also called a diverging mirror because it diverges parallel rays of light.

Uses of Convex Mirror Class 10

Why is Convex Mirror Used as Rear-view Mirror?

A convex mirror is used as a rear-view mirror because it always forms a virtual, erect and diminished image. It also provides a wider field of view, allowing the driver to see a larger area of traffic behind the vehicle.

Concave vs Convex Mirror Difference

Important Terms Related to Spherical Mirrors

Radius of Curvature and Focal Length Relation

For a spherical mirror:

R = 2f

or

f = R/2

This relation is often used in mirror formula numericals.

New Cartesian Sign Convention Class 10

The New Cartesian Sign Convention is used to assign positive and negative signs to distances in mirror and lens numericals.

Sign Convention for Mirrors Class 10

Sign Convention for Lenses Class 10

Exam Tip

Most mistakes in Light Reflection and Refraction numericals happen because of wrong signs. Always write u, v, f and their signs before substituting values in the formula.

Rules for Ray Diagrams of Spherical Mirrors

Ray diagrams help us find the position, size and nature of images formed by mirrors.

Ray Rules for Concave Mirror

Ray Rules for Convex Mirror

Ray Diagram for Concave Mirror Class 10

A concave mirror can form different types of images depending on the position of the object.

Image Formation Table for Concave Mirror

Most Important Concave Mirror Ray Diagrams

Students should practise these object positions carefully:

• Object at infinity
• Object beyond C
• Object at C
• Object between C and F
• Object at F
• Object between F and P

Ray Diagram for Convex Mirror Class 10

A convex mirror always forms a virtual, erect and diminished image.

Image Formation Table for Convex Mirror

Real and Virtual Image Difference Class 10

Mirror Formula Class 10

The mirror formula gives the relation between object distance, image distance and focal length.

1/v + 1/u = 1/f

Where:

Mirror Formula Numericals Class 10 Solved Example

Question: A concave mirror has focal length 20 cm. An object is placed at a distance of 30 cm in front of it. Find the image distance.

Given:

f = -20 cm
u = -30 cm
v = ?

Using mirror formula:

1/v + 1/u = 1/f

1/v + 1/(-30) = 1/(-20)

1/v - 1/30 = -1/20

1/v = -1/20 + 1/30

1/v = (-3 + 2)/60

1/v = -1/60

v = -60 cm

Answer: The image is formed 60 cm in front of the mirror. It is real and inverted.

Magnification Class 10

Magnification tells how many times the image is enlarged or diminished compared to the object.

Magnification Formula for Mirror

m = h'/h = -v/u

Where:

Interpretation of Magnification

Refraction of Light Class 10

Refraction of light is the bending of light when it passes from one transparent medium to another.

For example, a pencil partly immersed in water appears bent because light rays bend while moving from water to air.

Refraction of Light Definition Class 10

Refraction of light is the change in direction or bending of light when it passes obliquely from one transparent medium to another due to change in speed.

Why Does a Pencil Appear Bent in Water?

A pencil appears bent in water because light coming from the submerged part of the pencil bends when it passes from water to air. This bending of light is called refraction. Due to refraction, the underwater part appears to be at a different position.

Laws of Refraction Class 10

There are two laws of refraction.

First Law of Refraction

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

Second Law of Refraction / Snell’s Law

The ratio of sine of angle of incidence to sine of angle of refraction is constant for a given pair of media.

sin i / sin r = constant

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

Snell’s Law Class 10

Snell’s law explains the relation between angle of incidence and angle of refraction.

n₂₁ = sin i / sin r

Where:

Rarer to Denser Medium Bending Class 10

When light travels from a rarer medium to a denser medium, it bends towards the normal.

When light travels from a denser medium to a rarer medium, it bends away from the normal.

Example

When light travels from air to glass, it bends towards the normal. When it travels from glass to air, it bends away from the normal.

Refractive Index Class 10

Refractive index tells how much a medium bends light. It also tells how much the speed of light reduces in that medium.

Absolute Refractive Index Formula Class 10

n = c/v

Where:

Relative Refractive Index

Relative refractive index of medium 2 with respect to medium 1 is:

n₂₁ = v₁/v₂

Where:

• v₁ = speed of light in medium 1
• v₂ = speed of light in medium 2

Absolute vs Relative Refractive Index Class 10

Refractive Index Numericals Class 10

Example 1

Question: Speed of light in a medium is 2 × 10⁸ m/s. Find its refractive index.

Given:

c = 3 × 10⁸ m/s
v = 2 × 10⁸ m/s

Using:

n = c/v

n = (3 × 10⁸) / (2 × 10⁸)

n = 1.5

Answer: Refractive index of the medium is 1.5.

Refraction Through Glass Slab Class 10

When a ray of light passes through a rectangular glass slab, it bends twice:

1. It bends towards the normal when it enters the glass slab from air.
2. It bends away from the normal when it comes out from glass to air.

The emergent ray is parallel to the incident ray but shifted sideways. This sideways shift is called lateral displacement.

Lateral Displacement

Lateral displacement is the perpendicular distance between the incident ray’s original path and the emergent ray.

Refraction Through Glass Slab Result

Total Internal Reflection Class 10

Total internal reflection is the phenomenon in which light travelling from a denser medium to a rarer medium is completely reflected back into the denser medium.

This happens only when:

• Light travels from denser to rarer medium.
• Angle of incidence is greater than the critical angle.

Applications of Total Internal Reflection

Why Does a Diamond Sparkle?

A diamond sparkles because its high refractive index causes light to undergo multiple total internal reflections inside it. This traps and reflects light many times, making the diamond appear bright and sparkling.

Optical Fibre Working Class 10

Optical fibres work on the principle of total internal reflection. Light entering the fibre undergoes repeated total internal reflection and travels long distances with very little loss of intensity.

Spherical Lenses Class 10

A lens is a transparent medium bounded by two surfaces, at least one of which is spherical. Spherical lenses are mainly of two types:

1. Convex lens
2. Concave lens

Convex Lens Class 10

A convex lens is thicker at the centre and thinner at the edges. It is also called a converging lens because it converges parallel rays of light.

Uses of Convex Lens Class 10

Concave Lens Class 10

A concave lens is thinner at the centre and thicker at the edges. It is also called a diverging lens because it diverges parallel rays of light.

Uses of Concave Lens Class 10

Difference Between Concave and Convex Lens

Important Terms Related to Lenses

Ray Diagram for Convex Lens Class 10

A convex lens forms different images depending on the position of the object.

Image Formation Table for Convex Lens

Ray Diagram for Concave Lens Class 10

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

Image Formation Table for Concave Lens

Lens Formula Class 10

The lens formula gives the relation between object distance, image distance and focal length.

1/v - 1/u = 1/f

Where:

Lens Formula Numericals Class 10 Solved Example

Question: An object is placed at a distance of 30 cm from a convex lens of focal length 20 cm. Find the image distance.

Given:

u = -30 cm
f = +20 cm
v = ?

Using lens formula:

1/v - 1/u = 1/f

1/v - 1/(-30) = 1/20

1/v + 1/30 = 1/20

1/v = 1/20 - 1/30

1/v = (3 - 2)/60

1/v = 1/60

v = 60 cm

Answer: The image is formed 60 cm on the other side of the lens. It is real and inverted.

Magnification Formula for Lens Class 10

For lenses:

m = h'/h = v/u

Where:

Power of Lens Class 10

Power of a lens is the ability of a lens to converge or diverge light rays.

Power of Lens Formula

P = 1/f

Here, f is measured in metres.

Unit of Power

The SI unit of power of lens is dioptre, represented by D.

1 D = 1 m⁻¹

Sign of Power

Power of Lens Numericals Class 10

Question: Find the power of a convex lens of focal length 50 cm.

Given:

f = 50 cm = 0.5 m

Using:

P = 1/f

P = 1/0.5

P = +2 D

Answer: Power of the lens is +2 D.

All Formulas of Light Class 10

Use this formula sheet for quick revision before exams.

Light Reflection and Refraction Numericals Class 10

Numerical 1: Mirror Formula

Question: An object is placed 20 cm in front of a concave mirror of focal length 15 cm. Find the image distance.

Given:

u = -20 cm
f = -15 cm

Using:

1/v + 1/u = 1/f

1/v + 1/(-20) = 1/(-15)

1/v - 1/20 = -1/15

1/v = -1/15 + 1/20

1/v = (-4 + 3)/60

1/v = -1/60

v = -60 cm

Answer: Image is formed 60 cm in front of the mirror.

Numerical 2: Lens Formula

Question: An object is placed 15 cm from a convex lens of focal length 10 cm. Find image distance.

Given:

u = -15 cm
f = +10 cm

Using:

1/v - 1/u = 1/f

1/v - 1/(-15) = 1/10

1/v + 1/15 = 1/10

1/v = 1/10 - 1/15

1/v = (3 - 2)/30

1/v = 1/30

v = 30 cm

Answer: Image is formed 30 cm on the other side of the lens.

Numerical 3: Magnification

Question: An object of height 4 cm forms an image of height -8 cm. Find magnification.

Given:

h = 4 cm
h' = -8 cm

Using:

m = h'/h

m = -8/4

m = -2

Answer: Magnification is -2. The image is real, inverted and enlarged.

Numerical 4: Refractive Index

Question: The speed of light in glass is 2 × 10⁸ m/s. Find refractive index of glass.

n = c/v

n = (3 × 10⁸)/(2 × 10⁸)

n = 1.5

Answer: Refractive index of glass is 1.5.

Numerical 5: Power of Lens

Question: Find the power of a concave lens of focal length -25 cm.

f = -25 cm = -0.25 m

P = 1/f

P = 1/(-0.25)

P = -4 D

Answer: Power of the lens is -4 D.

Difference Between Reflection and Refraction

Difference Between Concave and Convex Lens

Difference Between Concave and Convex Mirror

Important Questions for Light Class 10

One-mark Questions

1. Define reflection of light.
2. State the laws of reflection.
3. What is refraction of light?
4. What is refractive index?
5. Write the mirror formula.
6. Write the lens formula.
7. What is power of a lens?
8. What is the SI unit of power of lens?
9. What is lateral displacement?
10. What is total internal reflection?

Two-mark Questions

1. Differentiate between reflection and refraction.
2. Write two uses of concave mirror.
3. Write two uses of convex mirror.
4. Differentiate between concave and convex lens.
5. Why is convex mirror used as rear-view mirror?
6. Why does a pencil appear bent in water?
7. Define real and virtual image.
8. Write the relation between radius of curvature and focal length.

Three-mark Questions

1. Draw ray diagram for image formation by concave mirror when object is beyond C.
2. Draw ray diagram for image formation by convex lens when object is between F and 2F.
3. Explain refraction through a glass slab.
4. Explain Snell’s law with formula.
5. Derive the nature of image formed by convex mirror.
6. Explain power of a lens and write its SI unit.

Five-mark Questions

1. Explain image formation by a concave mirror for different object positions using a table.
2. Explain image formation by a convex lens for different object positions using a table.
3. Write all formulas of Light Reflection and Refraction Class 10 and explain the symbols.
4. Solve a numerical based on mirror formula and magnification.
5. Explain refraction, refractive index and lateral displacement through a glass slab.

Light Reflection and Refraction Class 10 MCQ with Answers

1. The bouncing back of light from a surface is called:

A. Refraction
B. Reflection
C. Dispersion
D. Scattering

Answer: B. Reflection

2. The angle of incidence is equal to:

A. Angle of refraction
B. Angle of reflection
C. Angle of deviation
D. Critical angle

Answer: B. Angle of reflection

3. A convex mirror always forms an image that is:

A. Real and inverted
B. Virtual and erect
C. Real and enlarged
D. Real and same size

Answer: B. Virtual and erect

4. The mirror formula is:

A. 1/v - 1/u = 1/f
B. 1/v + 1/u = 1/f
C. v/u = f
D. P = 1/f

Answer: B. 1/v + 1/u = 1/f

5. The lens formula is:

A. 1/v - 1/u = 1/f
B. 1/v + 1/u = 1/f
C. m = -v/u
D. R = 2f

Answer: A. 1/v - 1/u = 1/f

6. A convex lens is also called:

A. Diverging lens
B. Converging lens
C. Plane lens
D. Reflecting lens

Answer: B. Converging lens

7. The SI unit of power of lens is:

A. metre
B. centimetre
C. dioptre
D. watt

Answer: C. Dioptre

8. Refractive index is given by:

A. n = v/c
B. n = c/v
C. n = u/v
D. n = f/R

Answer: B. n = c/v

9. The relation between radius of curvature and focal length is:

A. R = f
B. R = 2f
C. f = 2R
D. R = 1/f

Answer: B. R = 2f

10. A concave lens always forms an image that is:

A. Real and inverted
B. Virtual, erect and diminished
C. Real and enlarged
D. Virtual and enlarged

Answer: B. Virtual, erect and diminished

Assertion Reason Questions

Question 1

Assertion: A convex mirror is used as a rear-view mirror.
Reason: A convex mirror provides a wider field of view and forms virtual, erect and diminished images.

Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Question 2

Assertion: A pencil appears bent when partly immersed in water.
Reason: Light bends when it passes from water to air.

Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Question 3

Assertion: A concave mirror can form both real and virtual images.
Reason: The nature of image depends on the position of the object.

Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Question 4

Assertion: Power of a concave lens is negative.
Reason: Focal length of a concave lens is negative according to sign convention.

Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Question 5

Assertion: The emergent ray from a rectangular glass slab is parallel to the incident ray.
Reason: Refraction occurs at two parallel surfaces of the glass slab.

Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Case Study Questions on Light Reflection and Refraction

Case Study 1: Concave Mirror

A student places an object in front of a concave mirror. When the object is placed beyond the centre of curvature, the image is formed between focus and centre of curvature. The image is real, inverted and diminished.

Questions:

1. What type of mirror is used?
2. Where is the object placed?
3. Where is the image formed?
4. What is the nature of the image?
5. Write one use of this mirror.

Answers:

1. Concave mirror.
2. Beyond centre of curvature.
3. Between focus and centre of curvature.
4. Real, inverted and diminished.
5. It is used in headlights, shaving mirrors or solar furnaces.

Case Study 2: Glass Slab

A ray of light enters a rectangular glass slab from air. It bends towards the normal while entering the slab and bends away from the normal while coming out. The emergent ray is parallel to the incident ray but shifted sideways.

Questions:

1. What phenomenon is shown?
2. Why does light bend while entering glass?
3. What is lateral displacement?
4. How are incident ray and emergent ray related?
5. What happens when light enters along the normal?

Answers:

1. Refraction of light.
2. Because speed of light changes when it enters glass.
3. Lateral displacement is the sideways shift between incident ray path and emergent ray.
4. They are parallel.
5. No bending occurs.

Case Study 3: Convex Lens

A convex lens is used to form an image of an object. When the object is placed between F and 2F, the image is formed beyond 2F. The image is real, inverted and enlarged.

Questions:

1. What type of lens is used?
2. Where is the object placed?
3. Where is the image formed?
4. What is the nature of the image?
5. Write one use of convex lens.

Answers:

1. Convex lens.
2. Between F and 2F.
3. Beyond 2F.
4. Real, inverted and enlarged.
5. It is used in magnifying glasses, cameras, microscopes and telescopes.

NCERT Solutions Support for Light Reflection and Refraction Class 10

Students should solve NCERT Solutions for class 10 Science after revising the concepts. The most important NCERT question types include:

• Laws of reflection and refraction
• Mirror formula numericals
• Lens formula numericals
• Refractive index numericals
• Ray diagrams for concave mirror
• Ray diagrams for convex lens
• Power of lens questions
• Application-based questions like rear-view mirror and pencil in water

Important Diagrams for Light Reflection and Refraction Class 10

Students should practise these diagrams carefully:

Common Mistakes Students Should Avoid

Light Reflection and Refraction is one of the most important Physics chapters in Class 10 Science Syllabus. Students should focus on laws of reflection, laws of refraction, spherical mirrors, spherical lenses, sign convention, mirror formula, lens formula, refractive index, magnification, power of lens and ray diagrams.

For scoring well, practise all formulas, draw ray diagrams neatly, revise image formation tables and solve numericals step by step using the correct sign convention. Also practise MCQs, assertion-reason questions, case-based questions and important board-style questions for complete preparation.