Science · Class 8 · Chapter 10
Light: Mirrors and Lenses
Aim: Build a clear, working understanding of this chapter's key ideas, connected to real NCERT examples, worked problems, and everyday situations.
- Concave / Convex mirror — Curves inward / curves outward.
- Incident ray / Reflected ray — Light hitting a mirror / bouncing back.
- Normal — The perpendicular line at the point of reflection.
- Angle of incidence / reflection — Angles the rays make with the normal.
- Lens — Transparent material that bends light through it.
- Convex lens — Thicker in the middle; converges light.
- Concave lens — Thicker at the edges; diverges light.
- Lateral inversion — Left-right flip seen in a mirror image.
Chapter 10 · Concept 1 of 8
Concave and Convex Mirrors
- Concave mirror — Curves inward, like the inside of a spoon — made by coating the outer surface of curved glass.
- Convex mirror — Curves outward, like the back of a spoon — made by coating the inner surface.
Chapter 10 · Concept 2 of 8
Images and Everyday Uses
- Concave mirror — Close up: erect and enlarged. Farther away: inverted and smaller. Used in torch reflectors and dentists' mirrors.
- Convex mirror — Always erect and smaller than the object, whatever the distance. Used as vehicle side-mirrors and store surveillance mirrors, for a wider view.
Chapter 10 · Concept 3 of 8
The Laws of Reflection
- Two laws — The angle of incidence (i) always equals the angle of reflection (r). The incident ray, the normal, and the reflected ray all lie in the same plane.
Chapter 10 · Concept 4 of 8
Converging and Diverging Reflections
- Plane mirror — Parallel rays stay parallel.
- Concave mirror — Parallel rays converge to a point — concentrating sunlight enough to burn paper.
- Convex mirror — Parallel rays spread out (diverge).
Chapter 10 · Concept 5 of 8
Convex and Concave Lenses
- Convex lens — Thicker in the middle than at the edges — like a curved water drop, which magnifies text beneath it.
- Concave lens — Thicker at the edges than in the middle.
Chapter 10 · Concept 6 of 8
How Lenses Bend Light
- Convex lens (converging) — Close up: erect, enlarged image. Farther away: inverted, and eventually smaller. Can focus sunlight enough to burn paper.
- Concave lens (diverging) — Always gives an erect, smaller image — used together with convex lenses in eyeglasses, cameras, telescopes, and microscopes.
Chapter 10 · Concept 7 of 8
Comparing Mirrors
- Mirror | Image | Typical use
- Plane — Same size, erect — Everyday mirrors
- Concave — Enlarged near, inverted far — Torch reflector, dentist's mirror
- Convex — Always smaller, erect — Vehicle & safety mirrors
Chapter 10 · Concept 8 of 8
Comparing Lenses
- Lens | Behaviour | Image
- Convex — Converges light — Enlarged near, inverted far
- Concave — Diverges light — Always smaller, erect
Quick Recap
Check Your Understanding
- 1A light ray hits a mirror, making a 40° angle with the normal. What angle does the reflected ray make with the mirror itself?
- 2For a light ray falling exactly along the normal onto a tilted or untilted mirror, what is the angle of reflection in each case?
- 3A sketch-pen cap is placed in front of a plane mirror, a convex mirror, and a concave mirror. Match each resulting image to its mirror.