Class 10 Science Ch9 Notes Light Reflection & Refraction 2026 PDF

Students study the concepts of light reflection and refraction in Chapter 10 on Light of the 10th grade Science curriculum, with a focus on the straight-line propagation of light. These class 10 light chapter notes include everything you need: NCERT definitions, formulas, ray diagrams, short tricks and exam-focused tips that’ll save you during those night-before-the-exam panic scrolls. 

CBSE Class 10 Light, Reflection, and Refraction Notes

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What is Reflection of Light?

Reflection is when light bounces back after hitting a surface. The surface is called a reflecting surface. Reflection allows us to see objects around us because light from those objects enters our eyes.

a) Laws of Reflection

Reflection follows two fundamental laws:

1. First Law of Reflection:
   The angle of incidence (θᵢ) equals the angle of reflection (θᵣ).‍

θᵢ = θᵣ

2. Second Law of Reflection:
   The incident ray, reflected ray and the normal all lie in the same plane.

b) Types of Reflection

• Regular Reflection: Occurs on smooth surfaces like mirrors. Reflected rays are parallel → sharp images.
• Diffuse Reflection: Occurs on rough surfaces. Reflected rays scatter → diffused images.

c) Image Formation by Mirrors

• Plane Mirror: Produces a virtual, upright, same-size, laterally inverted image at the same distance behind the mirror.
• Concave Mirror: Curved inward. Can form real or virtual images depending on object distance.
  
• Object beyond focus → Real, inverted image
• Object between focus and mirror → Virtual, erect, magnified image‍
• Convex Mirror: Curved outward. Always forms virtual, erect, smaller images. Used in vehicle rearview mirrors.

What is Refraction of Light?

Refraction is the bending of light as it passes from one medium to another (e.g., air → water). It occurs because light changes speed in different media.

a) Laws of Refraction (Snell’s Law)

sin θᵢ/ sin θᵣ = v₁ / v₂ = n₂ /n₁

Where:

• θᵢ: Angle of incidence
• θᵣ: Angle of refraction
• v₁, v₂: Speed of light in first and second media
• n₁, n₂: Refractive indices of the media

Refractive Index: n = c / v (speed of light in vacuum / speed in medium)

• Air ≈ 1, Water ≈ 1.33

b) Total Internal Reflection (TIR)

Occurs when light travels from a denser to a rarer medium and the angle exceeds the critical angle.

Formula: sin θ_c = n₂ / n₁

• All light is reflected back → no refraction
• Used in optical fibers, periscopes and binoculars

Lenses and Image Formation

Lenses are transparent optical devices that refract light to form images.

a) Types of Lenses

Concave Lens (Diverging Lens):

• Thinner at center, thicker at edges
• Always forms virtual, erect, smaller images
• Used for myopia (nearsightedness)

Convex Lens (Converging Lens):

• Thicker at center
• Forms real or virtual images depending on object position
  
  1. Beyond focal point → Real, inverted image
  2. Between lens & focus → Virtual, erect, magnified image
• Used in magnifying glasses, microscopes, hypermetropia glasses

b) Lens Formula

Lens Formula is a mathematical relation that connects the focal length of a lens with the distance of the object and the distance of the image formed by the lens.

1 / f = 1/v - 1/u

f: Focal length, v: Image distance, u: Object distance

c) Magnification

Magnification is the measure of how much larger or smaller an image is compared to the object. It tells us how the size of the image changes after reflection or refraction.

For a lens, magnification (m) is given by:

m = height of image / height of object = v / u

where v is the image distance and u is the object distance.

d) Power of a Lens

Power of a Lens is a measure of the ability of a lens to converge or diverge light rays. It indicates how strong a lens is.

Power (P) is defined as the reciprocal of the focal length (f) in metres:

P = 1 / f

The unit of power is dioptre (D). A convex lens has positive power, while a concave lens has negative power.

e) Combination of Lenses (Thin Lenses in Contact)

Combination of Lenses refers to two or more thin lenses placed close together so that the distance between them is negligible.

In such a combination, the effective power of the lenses is equal to the algebraic sum of the powers of the individual lenses:

P = P₁ + P₂ (+ P₃ …)

This means the combination acts like a single lens with focal length f, where:

1/f = 1/f₁ + 1/f₂

It is commonly used in optical instruments like microscopes and telescopes to achieve the desired magnification.

Refraction through Prism

• Light bends when it passes through a prism due to change in optical density.
• Angle of deviation depends on angle of incidence and refractive index.
• Applications: Spectroscopy, splitting of light, optical instruments

Applications of Reflection and Refraction

• Cameras: Use lenses to focus light and form images
• Spectacles: Concave/convex lenses correct vision defects
• Microscopes & Telescopes: Use convex lenses for magnification
• Binoculars & Periscopes: Use mirrors and prisms to guide light
• Fiber Optics: Total internal reflection allows high-speed data transmission

In Class 10 Light notes, we’ve covered everything you need to learn and understand light and reflection class 10 notes thoroughly. These notes are perfectly designed to make revision fast, clear and exam-oriented.

When you’re revising before a test or practicing last-minute questions, these light reflection and refraction notes give you all the essentials in one place. Keep these handy for quick recalls and score confidently in your exams!

FAQs

Q1. What are the laws of reflection of light?

Ans. There are two laws of reflection: (1) The angle of incidence (θᵢ) is equal to the angle of reflection (θᵣ). (2) The incident ray, reflected ray and the normal to the surface all lie in the same plane. These laws govern how light bounces off surfaces.

Q2. How do plane mirrors form images differently from concave or convex mirrors?

Ans. Plane mirrors form virtual, upright and same-size images that appear at the same distance behind the mirror. Concave mirrors can form real or virtual images depending on object distance, while convex mirrors always form virtual, erect and diminished images.

Q3. What is the mirror formula and how is it used to calculate image distance or focal length?

Ans. The mirror formula is: 1/f = 1/v + 1/u, where f = focal length, v = image distance, u = object distance. Using this formula, you can calculate any one value if the other two are known.

Q4. How do we draw and interpret ray diagrams for spherical mirrors?

Ans. To draw a ray diagram: (1) Draw the principal axis and the mirror. (2) Draw at least two rays from the object: one parallel to the axis (reflects through focus) and one through the focus (reflects parallel). The intersection of reflected rays gives the image location, size and orientation.

Q5. Why is a virtual image formed by a convex mirror always diminished and erect?

Ans. Convex mirrors diverge light rays. The reflected rays appear to come from a point behind the mirror. Because the rays never actually meet, the image is virtual, smaller than the object and upright.