NCERT Curiosity · Class 7 · Science
Light: Shadows and Reflections
Riding through moonlit hills after watching fireflies, Keshav wonders: does the Moon make its own light, or just reflect the Sun's?
Key idea
Luminous and Non-luminous Objects
1
Luminous objects
Emit their own light — the Sun, stars, fire, lightning, and some animals.
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2
Non-luminous objects
Don't emit their own light — the Moon only reflects sunlight falling on it.
Key idea
Light Travels in a Straight Line
1
Three aligned holes
A light spot appears on a screen only when three matchbox holes line up perfectly.
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2
A bent pipe
A candle flame is visible through a straight pipe, but not through a bent one.
Key idea
Transparent, Translucent, and Opaque
Type | Light passes | Example
Almost completely — Glass
Only partially — Tracing paper
Key idea
How a Shadow Forms
A shadow needs three things: a light source, an opaque object, and a screen.
Key idea
What Changes a Shadow's Size
1
Object closer to the light
The shadow grows larger.
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2
Object closer to the screen
The shadow grows smaller and sharper. (Changing the object's colour never changes its shadow's colour.)
Key idea
Reflection of Light
A shiny surface or mirror changes the direction of light falling on it — this is reflection.
Seeing it happenA thin beam of light visibly changes path the moment it strikes a plane mirror.
Key idea
Images in a Plane Mirror
1
Same size
The image matches the object's size exactly.
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2
Erect
Upright, not upside down.
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3
Cannot be caught on a screen
It's a virtual image.
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4
Laterally inverted
Left and right are swapped.
Key idea
Why AMBULANCE Is Written Backwards
An ambulance's front has the word written mirror-reversed.
WhySo that a driver ahead, looking in their rear-view mirror, sees it laterally inverted back to normal, readable text.
Key idea
The Pinhole Camera
Light from an object passes through a tiny hole and forms an image on a screen inside.
The image formed is upside down (inverted) — unlike a mirror image, which is laterally inverted but right-side up.
Key idea
Periscope and Kaleidoscope
1
Periscope
Two plane mirrors in a Z-shaped tube let you see around a corner — used in submarines and tanks.
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2
Kaleidoscope
Three mirror strips arranged in a triangle create repeating patterns from small coloured objects through multiple reflections.
Chapter · Key terms to remember
Key Terms
Luminous / Non-luminous
Emits its own light / does not.
Transparent / Translucent / Opaque
Full / partial / no light passes through.
Shadow
Dark patch where an opaque object blocks light.
Chapter · Key terms to remember
More Key Terms
Reflection
Change in light's direction off a shiny surface.
Erect image
An upright, non-inverted image.
Lateral inversion
Left-right reversal in a mirror image.
Chapter · Key terms to remember
More Key Terms
Pinhole camera
Forms an inverted image via a tiny hole.
Periscope / Kaleidoscope
See around corners / view repeating patterns.
Questions for your notebook
Write these down, then discuss
1Which of these are luminous objects: Mars, Moon, Pole Star, Sun, Venus, Mirror?
2Match: Pinhole camera, Opaque object, Transparent object, Shadow — with: blocks light completely, dark region behind the object, forms an inverted image, light passes almost completely through.
3Four friends try to see a candle flame through a bent pipe with different sections. Who can actually see the flame?
Project as-is — students copy the questions, then the class discusses answers together.