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Chapter-Chapter 16. Light Science class 8 in english Medium CBSE Notes
CBSE Class 8 Science Notes in English Medium based on latest NCERT syllabus, covering definitions, diagrams, formulas, and exam-oriented explanations.
Chapter 16. Light
Properties of light
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Light travels in a straight line.
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Light does not need a medium (can travel through vacuum).
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The speed of light in air ≈ 3 × 10⁸ m/s.
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Reflection: Bouncing back of light from a surface.
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Laws of Reflection:
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Angle of incidence = Angle of reflection.
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Incident ray, reflected ray and normal lie in the same plane.
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Regular Reflection: Smooth surface (mirror), forms clear image.
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Diffuse Reflection: Rough surface, light scattered, no clear image.
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Plane Mirror:
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Image is virtual, erect, same size.
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Image is laterally inverted (left ↔ right).
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Multiple Reflection: When two mirrors are placed at an angle, multiple images are formed (used in kaleidoscope, periscope).
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Eye is like a camera, forms image on retina.
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Parts:
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Cornea: Transparent front covering.
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Iris: Coloured part, controls size of pupil.
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Pupil: Controls light entry.
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Lens: Converging lens, focuses light on retina.
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Retina: Light-sensitive layer.
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Optic nerve: Sends signals to brain.
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Blind spot: Point on retina where no vision is possible.
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Persistence of vision: Image stays on retina for 1/16th second.
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Myopia (Short-sightedness): Cannot see distant objects → corrected by concave lens.
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Hypermetropia (Long-sightedness): Cannot see nearby objects → corrected by convex lens.
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Proper lighting while reading.
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Balanced diet (Vitamin A prevents night blindness).
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Avoid watching screens for long time.
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Script for visually challenged people.
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Uses raised dots (patterns) to represent letters and words.
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Invented by Louis Braille.