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 1/v + 1/u = 1/f and magnification m = h’/h = -v/u.
9.3 Refraction of Light, Refractive Index & Spherical Lenses traces refraction through a rectangular glass slab, states Snell’s law (sin i / sin r = constant = n21), defines absolute refractive index n_m = c/v (with c = 3× 108 m s-1 and diamond at $n = 2.42$), draws ray diagrams for convex (converging) and concave (diverging) lenses, and applies the lens formula 1/v – 1/u = 1/f, magnification m = h’/h = v/u, and lens power P = 1 / f (in m) measured in dioptres (D).
Exercises in Chapter 9
- In-text Questions cover finding the focal length of a convex mirror of radius 32 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 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 D or -2.0 D lenses.
Read Class 10 Science Chapter 9 Online
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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 1/v + 1/u = 1/f (with magnification m = -v/u), whereas the spherical lens formula is 1/v – 1/u = 1/f (with magnification m = +v/u).