Class 10 Science Chapter 9 (formerly Chapter 10), Light – Reflection and Refraction, opens the physics section of the NCERT Class 10 Science textbook (2026-27). It covers image formation by spherical mirrors (concave and convex) and spherical lenses, the New Cartesian Sign Convention, the mirror and lens formulas, refractive index, Snell’s law, and power of a lens.
What Class 10 Science Chapter 9 Covers
9.1 & 9.2 Reflection of Light & Spherical Mirrors states the two laws of reflection, defines pole ($P$), centre of curvature ($C$), radius of curvature ($R = 2f$), principal axis and principal focus ($F$), draws ray diagrams for all six object positions of a concave mirror and two positions of a convex mirror (plus their practical uses in torches, headlights, shaving mirrors, solar furnaces and rear-view mirrors), and applies the mirror formula $\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$ and magnification $m = \frac{h’}{h} = -\frac{v}{u}$.
9.3 Refraction of Light, Refractive Index & Spherical Lenses traces refraction through a rectangular glass slab, states Snell’s law ($\frac{\sin i}{\sin r} = \text{constant} = n_{21}$), defines absolute refractive index $n_m = \frac{c}{v}$ (with $c = 3\times 10^8\text{ m s}^{-1}$ and diamond at $n = 2.42$), draws ray diagrams for convex (converging) and concave (diverging) lenses, and applies the lens formula $\frac{1}{v} – \frac{1}{u} = \frac{1}{f}$, magnification $m = \frac{h’}{h} = \frac{v}{u}$, and lens power $P = \frac{1}{f\text{ (in m)}}$ measured in dioptres ($\text{D}$).
Exercises in Chapter 9
- In-text Questions cover finding the focal length of a convex mirror of radius $32\text{ cm}$, why we prefer a convex mirror as a rear-view mirror in vehicles, meaning of the statement that the refractive index of diamond is $2.42$, and defining $1\text{ dioptre}$ of power of a lens.
- Chapter Exercises (17 Questions) provide numericals on mirror and lens image position, nature and size, refractive index calculations, and prescriptions with $+1.5\text{ D}$ or $-2.0\text{ D}$ lenses.
Read Class 10 Science Chapter 9 Online
More Chapters
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- Next: Chapter 10: The Human Eye and the Colourful World
- Hindi medium: Class 10 Science Chapter 9 PDF in Hindi (Vigyan)
- All Science chapters and the other Class 10 books: Class 10 NCERT books 2026-27
- All Class 1 to 12 NCERT Textbooks: NCERT Books PDF (Class 1–12)
FAQ
Why do we prefer a convex mirror as a rear-view mirror in vehicles?
A convex mirror always forms an erect, virtual and diminished image of objects behind the vehicle, and because it is curved outwards, it provides a much wider field of view than a plane mirror.
What is the mirror formula and how does it differ from the lens formula?
The spherical mirror formula is $\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$ (with magnification $m = -\frac{v}{u}$), whereas the spherical lens formula is $\frac{1}{v} – \frac{1}{u} = \frac{1}{f}$ (with magnification $m = +\frac{v}{u}$).