Chapter 11: Light: Shadows and Reflections NCERT Solutions Class 7th Science (Curiosity)

💡 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.

⭐ 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