NCERT Class 8 Science Chapter 10
Light: Mirrors and Lenses
NCERT Class 8 Science Chapter 10 explores the behaviour of light as it interacts with mirrors and lenses, forming the basis of optical instruments. This CBSE chapter covers reflection, refraction, types of mirrors (concave and convex), types of lenses (convex and concave), and how images are formed. Students understand the principles behind eyeglasses, cameras, telescopes, and the human eye.
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Key Terms
- Reflection
- The bouncing back of light rays when they hit a smooth, shiny surface; governed by the laws of reflection.
- Refraction
- The bending of light as it passes from one medium to another with a different optical density (e.g., air to water), causing a change in speed.
- Concave Mirror
- A curved mirror with a reflecting surface that curves inward (like a spoon's inner side); converges light rays and forms real, inverted images (used in torches, headlights, and solar concentrators).
- Convex Mirror
- A curved mirror with a reflecting surface that curves outward; diverges light rays and always forms virtual, erect, and diminished images (used as rear-view mirrors in vehicles).
- Convex Lens
- A lens that is thicker at the centre than at the edges; converges (brings together) light rays and forms real or virtual images depending on object distance.
- Concave Lens
- A lens that is thinner at the centre than at the edges; diverges light rays and always forms a virtual, erect, diminished image (used to correct short-sightedness).
- Focal Length
- The distance between the centre of a mirror or lens and its focal point, where parallel rays converge after reflection or refraction.
Frequently Asked Questions
What is the difference between concave and convex mirror Class 8?▾
A concave mirror has a reflecting surface that curves inward — it converges light and can form both real and virtual images depending on where the object is. A convex mirror curves outward — it always diverges light and forms virtual, erect, smaller images. Rear-view mirrors in cars are convex; shaving mirrors are concave.
What is the difference between concave and convex lens Class 8 Science?▾
A convex (converging) lens is thicker at the centre; it bends light rays inward (converges them) and is used to correct long-sightedness and in magnifying glasses. A concave (diverging) lens is thinner at the centre; it spreads light rays outward (diverges them) and is used to correct short-sightedness.
What are the laws of reflection Class 8 NCERT?▾
The two laws of reflection are: (1) The angle of incidence equals the angle of reflection (both measured from the normal to the surface at the point of incidence). (2) The incident ray, the reflected ray, and the normal all lie in the same plane. These laws apply to all types of mirrors.
What is refraction of light Class 8?▾
Refraction is the bending of light when it passes from one medium to another (e.g., from air to glass or water). It occurs because light changes speed when it enters a denser or less dense medium. Refraction causes a straw to appear bent when placed in water and makes swimming pools look shallower than they are.
How do glasses correct vision problems Class 8?▾
Concave lenses are used in spectacles to correct short-sightedness (myopia) — they diverge light so it focuses on the retina. Convex lenses correct long-sightedness (hypermetropia) — they converge light to help the eye focus on nearby objects. The correct lens adjusts where light focuses on the retina.
What are the uses of concave and convex mirrors Class 8?▾
Concave mirrors are used in: torches and headlights (to produce parallel beams), shaving/makeup mirrors (produce magnified image), solar cookers (concentrate sunlight). Convex mirrors are used as: rear-view mirrors in vehicles (wide field of view), security mirrors in shops. NCERT Class 8 Chapter 10 covers all these applications.
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