Science · Class 7 · Chapter 11
Light: Shadows and Reflections
Aim: Build a clear, working understanding of this chapter's key ideas, connected to real NCERT examples, worked problems, and everyday situations.
- 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.
- 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.
- Pinhole camera — Forms an inverted image via a tiny hole.
- Periscope / Kaleidoscope — See around corners / view repeating patterns.
Chapter 11 · Concept 1 of 10
Luminous and Non-luminous Objects
- Luminous objects — Emit their own light — the Sun, stars, fire, lightning, and some animals.
- Non-luminous objects — Don't emit their own light — the Moon only reflects sunlight falling on it.
Chapter 11 · Concept 2 of 10
Light Travels in a Straight Line
- Three aligned holes — A light spot appears on a screen only when three matchbox holes line up perfectly.
- A bent pipe — A candle flame is visible through a straight pipe, but not through a bent one.
Chapter 11 · Concept 3 of 10
Transparent, Translucent, and Opaque
- Type | Light passes | Example
- Transparent — Almost completely — Glass
- Translucent — Only partially — Tracing paper
- Opaque — Not at all — Cardboard
Chapter 11 · Concept 4 of 10
How a Shadow Forms
- A shadow needs three things: a light source, an opaque object, and a screen.
Chapter 11 · Concept 5 of 10
What Changes a Shadow's Size
- Object closer to the light — The shadow grows larger.
- Object closer to the screen — The shadow grows smaller and sharper. (Changing the object's colour never changes its shadow's colour.)
Chapter 11 · Concept 6 of 10
Reflection of Light
- A shiny surface or mirror changes the direction of light falling on it — this is reflection.
- Seeing it happen — A thin beam of light visibly changes path the moment it strikes a plane mirror.
Chapter 11 · Concept 7 of 10
Images in a Plane Mirror
- Same size — The image matches the object's size exactly.
- Erect — Upright, not upside down.
- Cannot be caught on a screen — It's a virtual image.
- Laterally inverted — Left and right are swapped.
Chapter 11 · Concept 8 of 10
Why AMBULANCE Is Written Backwards
- An ambulance's front has the word written mirror-reversed.
- Why — So that a driver ahead, looking in their rear-view mirror, sees it laterally inverted back to normal, readable text.
Chapter 11 · Concept 9 of 10
The Pinhole Camera
- Light from an object passes through a tiny hole and forms an image on a screen inside.
- Inverted, not reversed — The image formed is upside down (inverted) — unlike a mirror image, which is laterally inverted but right-side up.
Chapter 11 · Concept 10 of 10
Periscope and Kaleidoscope
- Periscope — Two plane mirrors in a Z-shaped tube let you see around a corner — used in submarines and tanks.
- Kaleidoscope — Three mirror strips arranged in a triangle create repeating patterns from small coloured objects through multiple reflections.
Quick Recap
Check Your Understanding
- 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?