🔬 Chapter 11 — Light: Shadows and Reflections
Class 7 Science | Curiosity | EduGrown Notes
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💡 Light — Shadows and Reflections! How we see the world around us!
💡 Sources of Light
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✨Luminous objects = objects that emit their own light | e.g., Sun, stars, fire, fireflies, electric bulbs
🌑Non-luminous objects = objects that reflect light but do not emit their own | e.g., Moon, walls, books, furniture
🌙The Moon is non-luminous — it only reflects sunlight! Moonlight = reflected sunlight!
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💡 Sources of electric light — LED, CFL, incandescent bulbs
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🔥 Natural sources of light — fire, stars, luminous animals
📏 Light Travels in Straight Lines
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📏Light always travels in a straight line — this is why we cannot see around corners!
🔦Proof: Light through 3 matchboxes (all holes in line = light passes; one misaligned = no light!)
🕯️Also proved: Light visible through a straight pipe, but NOT through a bent pipe
🔦 Light Through Different Materials
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✅ Transparent
→Light passes through completely
→Objects can be seen clearly through it
→e.g., clear glass, water, air
🌫️ Translucent
→Light passes through partially
→Objects appear blurry/hazy
→e.g., frosted glass, wax paper, tissue paper
❌ Opaque
→Light does not pass through at all
→Forms shadows!
→e.g., cardboard, wood, metal
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🔦 Light through transparent, translucent and opaque materials
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🌑 Shadows formed when opaque objects block light!
🌑 Shadows & Reflection
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🌑Shadow = dark area formed behind an opaque object when it blocks light
☀️Shadow is longer when light source is at an angle (morning/evening) | shorter when light is directly above (noon)
🪞Reflection = bouncing back of light from a surface
🪞Mirrors have very smooth surfaces → reflect light clearly → form clear images
💡Laws of Reflection: Angle of incidence = Angle of reflection (light bounces at the same angle it hits!)
💡 LED Lights — India's Green Initiative!
LED (Light Emitting Diode) lamps use much less electricity than traditional bulbs, are brighter and last longer!
India's government promoted LED lamps nationwide — saving crores of rupees in electricity bills & reducing carbon emissions! 🌍✨
LED lamps must be recycled properly (not thrown in garbage) — they contain electronic components.
India's government promoted LED lamps nationwide — saving crores of rupees in electricity bills & reducing carbon emissions! 🌍✨
LED lamps must be recycled properly (not thrown in garbage) — they contain electronic components.
⭐ Quick Summary
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📝 Key Points
💡Luminous = emits own light (Sun, bulb) | Non-luminous = reflects light (Moon, book)
📏Light travels in straight lines — proven by matchbox activity and pipe experiment
🔦Transparent (clear glass) → Translucent (frosted glass) → Opaque (cardboard) — different light passage
🌑Shadow = opaque object blocks light | Reflection: angle of incidence = angle of reflection