Many students feel stressed about drawing complex ray diagrams and getting confused by tricky "plus-minus" sign conventions as the CBSE 10th board exam on February 25, 2026 gets closer. Trying to learn every long derivation at the last minute can be confusing, especially when you have to solve high-weightage numericals quickly in the exam hall.
Class 10 Light Reflection and Refraction Notes solve this problem by giving you a simple, exam-focused plan. Instead of long, boring theory, these notes focus on the "must-know" logic for mirrors and lenses, easy step-by-step ray diagrams, and short formulas for focal length and magnification.
By focusing on topics that always come in board papers, like how light works in spectacles, cameras, and car rear-view mirrors, this content helps you revise fast. It ensures you can solve even the toughest physics problems with confidence in those final hours before the exam.
Light Reflection and Refraction Class 10 Explanation
Light interacts with objects in two main ways: reflection and refraction. Reflection is the bouncing back of light from a surface, while refraction is the bending of light as it passes through different media.
These CBSE Class 10 Science Chapter 9 notes provide a concise overview of these phenomena, crucial for a strong foundation in light reflection and refraction class 10.
Class 10 Physics Light Reflection and Refraction
Class 10 Physics Light Reflection and Refraction explains how light behaves when it bounces off surfaces or passes from one medium to another.
It covers laws of reflection and refraction, image formation by mirrors and lenses, and practical applications in everyday life.
Reflection of Light
Reflection occurs when light hits a polished surface, like a mirror, and bounces back into the same medium.
The Laws of Reflection are:
-
The angle of incidence equals the angle of reflection (angle i = angle r).
-
The incident ray, the reflected ray, and the normal to the surface at the point of incidence all lie in the same plane.
Spherical Mirrors
Spherical mirrors are curved mirrors that form part of a sphere. They are of two types: concave and convex. Key terms associated with them include:
-
Pole (P): The center point of the mirror's reflecting surface.
-
Centre of Curvature (C): The center of the sphere from which the mirror is a part.
-
Principal Axis (PA): The straight line passing through the Pole and the Centre of Curvature.
-
Radius of Curvature (R): The distance between the Pole and the Centre of Curvature (R = 2f).
-
Principal Focus (F): The point on the principal axis where parallel rays converge (concave) or appear to diverge from (convex) after reflection.
-
Focal Length (f): The distance between the Pole and the Principal Focus.
Image Formation by Concave Mirror
Concave mirrors can form both real and virtual images depending on the object's position. Real images are formed when reflected rays actually meet and are typically inverted. Virtual images form when rays appear to meet and are always erect.
| Position of the Object | Position of the Image | Size of the Image | Nature of the Image |
|---|---|---|---|
| At infinity | At the focus F | Highly diminished, point-sized | Real and inverted |
| Beyond 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 |
Uses of Concave Mirror
Concave mirrors are used in various applications due to their converging property.
-
Shaving mirrors to see magnified images.
-
Dentist's mirrors to examine teeth.
-
Headlights of cars and searchlights to produce powerful parallel beams.
-
Solar furnaces to concentrate sunlight.
Image Formation by Convex Mirror
Convex mirrors always form virtual, erect, and diminished images, regardless of the object's position.
| Position of the Object | Position of the Image | Size of the Image | Nature of the Image |
|---|---|---|---|
| At infinity | At the focus F | Highly diminished, point-sized | Virtual and erect |
| Between infinity and the pole P | Between F and P | Diminished | Virtual and erect |
Uses of Convex Mirror
Convex mirrors provide a wider field of view.
-
Rear-view mirrors in vehicles.
-
Security mirrors in shops.
Sign Convention for Spherical Mirrors
The Cartesian Sign Convention is used for mirror calculations.
-
All distances are measured from the Pole (P).
-
Distances measured in the direction of incident light are positive; those against are negative.
-
Heights measured upward (above principal axis) are positive; downward are negative.
Refraction of Light
Refraction is the phenomenon of light bending as it travels from one transparent medium to another.
This bending occurs because the speed of light changes when it moves from one medium to another.
Refractive Index
The refractive index (n) of a medium quantifies how much light bends when entering it.
-
Absolute Refractive Index:
where c is the speed of light in vacuum (3 x 10^8 m/s) and V is the speed of light in the medium. -
Relative Refractive Index: The refractive index of medium 2 with respect to medium 1 is
A higher refractive index means a denser medium and slower light speed.
Laws of Refraction (Snell's Law)
The Laws of Refraction describe how light behaves when passing between two media.
-
The incident ray, the refracted ray, and the normal to the interface at the point of incidence all lie in the same plane.
-
The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media. This is Snell's Law:
Spherical Lenses
Lenses are transparent materials bounded by two spherical surfaces or one spherical and one plane surface.
-
Convex Lens (Converging Lens): Thicker in the middle, converges parallel light rays.
-
Concave Lens (Diverging Lens): Thinner in the middle, diverges parallel light rays.
-
Optical Centre (O): The central point of the lens through which light passes undeviated.
-
Principal Focus (F) and Focal Length (f): Similar to mirrors, but lenses have two focal points (F1, F2) on either side.
Image Formation by Convex Lens
Convex lenses form images with varied characteristics, depending on the object's position. This topic is key in class 10 physics light reflection and refraction.
| Position of the object | Position of the image | Relative size of the image | Nature of the image |
|---|---|---|---|
| At infinity | At focus F₂ | Highly diminished, point-sized | Real and inverted |
| Beyond 2F₁ | Between F₂ and 2F₂ | Diminished | Real and inverted |
| At 2F₁ | At 2F₂ | Same size | Real and inverted |
| Between F₁ and 2F₁ | Beyond 2F₂ | Enlarged | Real and inverted |
| At focus F₁ | At infinity | Infinitely large or highly enlarged | Real and inverted |
| Between F₁ and optical centre O | On the same side of the lens as the object | Enlarged | Virtual and erect |
Image Formation by Concave Lens
Concave lenses always form virtual, erect, and diminished images.
| Position of the object | Position of the image | Relative size of the image | Nature of the image |
|---|---|---|---|
| At infinity | At focus F₁ | Highly diminished, point-sized | Virtual and erect |
| Between infinity and optical centre O | Between focus F₁ and optical centre O | Diminished | Virtual and erect |
Sign Convention for Spherical Lenses
The Cartesian Sign Convention is adapted for lenses:
-
All distances are measured from the Optical Centre (O).
-
Directions and heights follow the same rules as for mirrors.
Key Rules of Light: Reflection and Refraction
These formulas are vital for solving numerical problems in light reflection and refraction class 10.
Mirror Formula
The relationship between object distance (mu), image distance (V), and focal length (f) for spherical mirrors is:
-
Note: Object distance (mu) is always taken as negative. Convex mirror has positive 'f', concave mirror has negative 'f'.
Magnification (Mirrors)
Magnification (m) describes the relative size of the image to the object.
-
hi: height of image, h0: height of object.
-
Positive m indicates virtual and erect image.
-
Negative m indicates real and inverted image.
-
|m| > 1 means enlarged, |m| < 1 means diminished, |m| = 1 means same size.
Lens Formula
The relationship between object distance (mu), image distance (V), and focal length (f) for spherical lenses is:
-
Note: Convex lens has positive 'f', concave lens has negative 'f'.
Magnification (Lenses)
For lenses, magnification (m) is given by:
-
Positive m indicates virtual and erect image.
-
Negative m indicates real and inverted image.
Power of a Lens
The power of a lens (P) measures its ability to converge or diverge light rays.
(where f is in meters).
-
The unit of power is Dioptre (D).
-
A convex lens has positive power, a concave lens has negative power.
-
For a combination of lenses,
Light Reflection and Refraction Class 10 Notes PDF Download
Light Reflection and Refraction Class 10 Notes provides a comprehensive guide to the fundamental concepts of light, including laws of reflection and refraction, image formation by mirrors and lenses, and practical applications. This Class 10 light reflection and refraction notes PDF download is designed for easy revision, clear understanding, and quick preparation for CBSE board exams, helping students grasp important formulas, diagrams, and examples in one place.
Light Reflection and Refraction Class 10 Notes PDF Download
Top Repeated Board Questions (Don't Skip These!)
Based on the last 10 years of CBSE Science papers, these patterns have the highest probability of appearing in your final assessment. As the CBSE Class 10 Science board exam is scheduled for February 25, 2026, mastering these specific patterns now will ensure you don't lose easy marks under time pressure.
-
The "Special Case" Ray Diagram:
Question: Draw a ray diagram for a concave mirror when the object is between the Pole (P) and Focus (F).
Exam Tip: This is the most repeated diagram because it is the only case where a concave mirror forms a virtual, erect, and magnified image. Examiners love it! -
The Power of Lens Numerical:
Question: Calculate the power of a lens with a focal length of -20 cm. What type of lens is it?
Exam Hack: Always convert focal length to meters before using the formula:
P = 1 divided by f
Since the focal length is negative, it is a concave (diverging) lens. -
Refractive Index Logic:
Question: If the refractive index of glass is 1.5 and water is 1.33, in which medium does light travel faster?
Exam Tip: Use the inverse relationship:
Higher refractive index (n) = Lower speed of light (v)
Light travels faster in water. -
The "Sign Convention" Trap:
Common Mistake: Students often forget that for convex mirrors, the focal length (f) is always positive, while for concave mirrors, it is always negative. One wrong sign in the mirror formula:
1 divided by v + 1 divided by u = 1 divided by f
will lead to a wrong answer. -
Practical Applications:
Question: Why are convex mirrors used as rear-view mirrors in vehicles?
Must-Include Keywords: “Wide field of view,” “Erect image,” and “Diminished size.”
Related Links