New NCERT Curiosity · Class 8 Science · Term II · Chapter 10: Light: Mirrors and Lenses
This chapter introduces spherical mirrors — concave and convex — and the images they form. It explains the two laws of reflection and then describes convex and concave lenses, how they bend light and where they are used.
From the Class 8 Science Short Notes, made as per the new NCERT book Curiosity · Pages 60–65 of the book.
Key points
- A spherical mirror's reflecting surface is like part of a hollow sphere.
- A concave mirror curves inwards; a convex mirror curves outwards.
- A plane mirror always gives an erect image of the same size.
- A concave mirror gives an erect, enlarged image when the object is close; farther away the image becomes inverted.
- A convex mirror always gives an erect, diminished image.
- Concave mirrors are used in torches, headlights, dentist's mirrors, telescopes and solar cookers.
- Convex mirrors are used as side-view mirrors, road-safety mirrors and surveillance mirrors.
- A concave mirror converges parallel beams; a convex mirror diverges them.
- A lens is transparent with curved surfaces; we see through it, not in it.
- A convex lens is thicker in the middle and converges light; a concave lens is thicker at the edges and diverges light.
- Lenses are used in magnifying glasses, eyeglasses, cameras, telescopes and microscopes; our eye has a convex lens.
Formulas
| First law of reflection | ∠i = ∠r Angle of incidence equals angle of reflection. |
| Angle with the mirror | Angle with mirror = 90° − ∠r e.g. ∠r = 40° → 90° − 40° = 50°. |
Key terms
- Spherical mirror: A mirror whose reflecting surface is spherical, like part of a hollow sphere.
- Concave mirror: A mirror whose reflecting surface curves inwards.
- Convex mirror: A mirror whose reflecting surface curves outwards.
- Normal: A line at 90° to the mirror at the point of incidence.
- Angle of incidence: The angle between the incident ray and the normal.
- Angle of reflection: The angle between the reflected ray and the normal.
- Lens: A piece of transparent material with curved surfaces through which light passes.
- Solar concentrator: A device that concentrates sunlight into a small area using mirrors or lenses.
Diagrams to learn
- Reflection from a plane mirror (Fig 10.1)
- Parallel beams falling on mirrors and lenses (Fig 10.2)
- Table of images formed by plane, concave and convex mirrors
- Table of images formed by convex lens, concave lens and flat glass
- Table comparing concave and convex mirrors and lenses
- A convex side mirror shows vehicles smaller, so 'Objects in mirror are closer than they appear'.
- The laws of reflection hold for all mirrors — plane, concave and convex.
- Mirrors and lenses behave opposite: a concave mirror and a convex lens converge light; a convex mirror and a concave lens diverge it.
- Never look at the Sun, or at sunlight reflected by a mirror or focused by a lens.
A real page from the book
Get the full chapter in the book
This page is a summary. The Class 8 Science Short Notes has the complete chapter in colour, with every diagram and worked example.
Frequently asked questions
What are the laws of reflection?
First, the angle of incidence equals the angle of reflection. Second, the incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane.
Why is a convex mirror used as a side-view mirror?
It always gives an erect, smaller image and a much wider view of the road behind.
What is the difference between a convex and a concave lens?
A convex lens is thicker in the middle and converges light. A concave lens is thicker at the edges, diverges light and always gives an erect, diminished image.
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