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Physics · Class 10 · Chapter 13: Propagation and Reflection of Light

8 min

Key points

Light is a form of energy that travels in straight lines in a homogeneous medium
The speed of light in vacuum is 3 × 10⁸ m/s and decreases when light enters a denser medium
Reflection occurs when light bounces back after striking a surface without changing medium
The incident ray, reflected ray, and normal all lie in the same plane at the point of incidence
Angle of incidence equals angle of reflection (∠i = ∠r) - First Law of Reflection
Regular reflection occurs from smooth surfaces like plane mirrors, while diffused reflection occurs from rough surfaces
Real images can be obtained on screen while virtual images cannot be obtained on screen
A plane mirror forms virtual, erect, same-sized images at equal distance behind the mirror
Lateral inversion means left appears as right and vice versa in plane mirror reflection

Definitions

Reflection of Light: The bouncing back of light when it strikes a surface and returns to the same medium from which it came
Incident Ray: The ray of light that strikes the reflecting surface
Reflected Ray: The ray of light that bounces back from the reflecting surface
Normal: A line drawn perpendicular to the reflecting surface at the point of incidence
Real Image: An image that can be obtained on a screen and is formed by the actual intersection of light rays

Worked example

Define reflection of light. State the two laws of reflection. Draw a labeled diagram showing reflection of light from a plane mirror. (6 marks)

Reflection of light: The bouncing back of light rays when they strike a surface is called reflection of light. Laws of Reflection: (1) The incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane. (2) The angle of incidence is equal to the angle of reflection. [Diagram showing plane mirror with incident ray, reflected ray, normal, angle i = angle r, point of incidence labeled]

Common mistakes

Students confuse incident ray with reflected ray in diagrams
Writing angle of reflection = 90° - angle of incidence instead of equal angles
Forgetting to draw normal as perpendicular line in reflection diagrams
Confusing real and virtual images - remember real images can be obtained on screen
Not showing lateral inversion when drawing image formation by plane mirror

Quick recap

Light propagates in straight lines through homogeneous media. Reflection occurs when light bounces back from surfaces following two laws: rays and normal lie in same plane, and angle of incidence equals angle of reflection. Regular reflection occurs from smooth surfaces while irregular reflection occurs from rough surfaces. Plane mirrors form virtual, erect, same-sized images at equal distance behind the mirror.

Generated by AI from Sindh Textbook Board material; review state: ai_unreviewed. MCQs, past-paper references and examiner notes are held back until a teacher has checked them.