CBSE Class 10 Science: Light — Reflection & Refraction Notes 2026

Reflection of Light

• Laws of reflection: angle of incidence = angle of reflection; incident ray, normal and reflected ray are coplanar
• Types of reflection: regular (smooth surface) and diffuse (rough surface)
• Plane mirror: virtual, erect, same size, laterally inverted image; image distance = object distance

Spherical Mirrors

• Concave mirror: converging; centre of curvature C, principal focus F, focal length f = R/2
• Mirror formula: 1/v + 1/u = 1/f; magnification m = −v/u
• Real, inverted, magnified image (object between F and C): used in headlights, solar furnaces; virtual erect image (object inside F): shaving mirror

Refraction of Light

• Bending of light when passing from one medium to another due to change in speed
• Snell's law: n₁ sin i = n₂ sin r; refractive index n = c/v
• Apparent depth: object in water appears shallower; real depth/apparent depth = n

Refraction Through Spherical Lenses

• Convex (converging) lens: focal length positive; concave (diverging): negative (new Cartesian convention)
• Lens formula: 1/v − 1/u = 1/f; magnification m = v/u = h'/h
• Power of lens P = 1/f (metres); unit dioptre; total power of lenses: P = P₁ + P₂

Image Formation by Lenses

• Convex lens at object beyond 2F: real, inverted, diminished — camera, eye
• Convex lens at object between F and O: virtual, erect, magnified — magnifying glass
• Concave lens: always virtual, erect, diminished regardless of object position

Human Eye and Defects

• Normal eye: near point 25 cm, far point infinity; accommodation by ciliary muscles changing lens shape
• Myopia (near-sightedness): far point < infinity; image in front of retina; corrected by concave lens
• Hypermetropia (far-sightedness): near point > 25 cm; image behind retina; corrected by convex lens

CBSE Numericals

• Concave mirror: f = −15 cm, object at −30 cm; find image position by mirror formula
• Power of combination of +3D and −1D lenses placed in contact
• Person's near point is 50 cm; find power of lens needed for normal reading