NCERT Curiosity · Class 8 · Science
Light: Mirrors and Lenses
At a science centre, Meena's face looks huge in one curved mirror, tiny in another, and upside down in a third. Why do curved mirrors behave so differently from flat ones?
Key idea
Concave and Convex Mirrors
1
Concave mirror
Curves inward, like the inside of a spoon — made by coating the outer surface of curved glass.
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2
Convex mirror
Curves outward, like the back of a spoon — made by coating the inner surface.
Key idea
Images and Everyday Uses
1
Concave mirror
Close up: erect and enlarged. Farther away: inverted and smaller. Used in torch reflectors and dentists' mirrors.
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2
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.
Key idea
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.
Key idea
Converging and Diverging Reflections
1
Plane mirror
Parallel rays stay parallel.
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2
Concave mirror
Parallel rays converge to a point — concentrating sunlight enough to burn paper.
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3
Convex mirror
Parallel rays spread out (diverge).
Key idea
Convex and Concave Lenses
1
Convex lens
Thicker in the middle than at the edges — like a curved water drop, which magnifies text beneath it.
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2
Concave lens
Thicker at the edges than in the middle.
Key idea
How Lenses Bend Light
1
Convex lens (converging)
Close up: erect, enlarged image. Farther away: inverted, and eventually smaller. Can focus sunlight enough to burn paper.
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2
Concave lens (diverging)
Always gives an erect, smaller image — used together with convex lenses in eyeglasses, cameras, telescopes, and microscopes.
Key idea
Comparing Mirrors
Mirror | Image | Typical use
Same size, erect — Everyday mirrors
Enlarged near, inverted far — Torch reflector, dentist's mirror
Always smaller, erect — Vehicle & safety mirrors
Key idea
Comparing Lenses
ConvexConverges light — Enlarged near, inverted far
ConcaveDiverges light — Always smaller, erect
Chapter · Key terms to remember
Key Terms
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.
Chapter · Key terms to remember
More Key Terms
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.
Chapter · Key terms to remember
More Key Terms
Concave lens
Thicker at the edges; diverges light.
Lateral inversion
Left-right flip seen in a mirror image.
Questions for your notebook
Write these down, then discuss
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.
Project as-is — students copy the questions, then the class discusses answers together.