Class 10 Science Chapter 9: Light – Reflection and Refraction

Chapter 9 of the NCERT Class 10 Science textbook “Science”.

Chapter at a glance

This part introduces how we describe light rays and how light bounces from smooth surfaces. You will learn the two laws of reflection and how a plane mirror forms images. We explain image location, size, laterally inverted images and simple ray diagrams. Examples and short exercises help practise drawing and reasoning.

What you will learn: You learn the ray model of light, the laws of reflection, construction of ray diagrams for plane mirrors, and predictions about image position and size.

Why it matters: These ideas explain everyday reflections (mirrors, shiny water, polished metal) and are the foundation for understanding curved mirrors and refraction later.

Key concepts

Ray model of light — Light travels in straight lines called rays in uniform media.
Laws of reflection — Angle of incidence equals angle of reflection and both lie in the same plane.
Image in a plane mirror — Plane mirror produces a virtual, upright image equal distance behind as the object is in front.
Lateral inversion — Mirror swapping left and right is lateral inversion, not top-bottom swap.

What the chapter covers

Try at Home — A safe activity to see virtual images and lateral inversion.
Why Questions — Short reasoned answers to help deepen understanding.

Remember for the exam

Measure angles from the normal, not from the mirror surface.
Virtual images cannot be formed on a screen.

Common mistakes

Mistake: Measuring angles from the mirror surface instead of the normal. Better: Always draw the normal at the point of incidence and measure angles from it.
Mistake: Saying the image formed by a plane mirror is real because it looks real. Better: Call it virtual and explain that rays only appear to come from behind the mirror.
Mistake: Not extending reflected rays backward when locating the virtual image. Better: Use dashed lines to extend reflected rays behind the mirror to locate the image.

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