Class 7 Science Chapter 11: Light – Shadows and Reflections | NCERT Notes, Luminous & Non‑Luminous Objects, Straight Line Propagation, Pinhole Camera & Mirror Images,25+ Practice Questions & Answers, CBSE Board Exams
Complete Chapter 11 guide: natural and artificial sources of light (Sun, stars, fire, LEDs), luminous vs non‑luminous objects, light travelling in straight lines (matchbox and pipe activities), formation of shadows (umbra/penumbra), eclipses idea link, simple pinhole camera, reflection from plane mirrors, everyday applications, LED energy saving note, plus exam-oriented definitions, diagrams, and conceptual questions for CBSE
Updated: 6 months ago
Light: Shadows and Reflections
Class 7 Science Chapter 11 | Complete NCERT Guide | Sources of Light, Rectilinear Propagation, Shadows, Reflections
Full Chapter Summary & Detailed Notes – Light: Shadows and Reflections
Introduction
Keshav and Jatin enjoy watching fireflies at night in rural Maharashtra. Fireflies produce their own light. The moon, however, only reflects sunlight. This leads to the central questions of the chapter:
- What objects produce their own light?
- How does light travel?
- Why do we see shadows and reflections?
11.1 Sources of Light
Natural Sources: Sun, stars, lightning, fireflies, glow-worms, some deep-sea creatures (bioluminescence).
Artificial Sources:
- Ancient → fire (wood, animal fat, oil lamps, candles)
- Modern → incandescent bulbs, tube lights, CFL, LED
Luminous objects → emit their own light (Sun, bulb, firefly)
Non-luminous objects → do not emit light; visible only when light falls on them and reflects (Moon, book, table, human body)
Science & Society Box
LED lamps → consume very less electricity, brighter, last 10–15 years, environment-friendly. Indian government promotes them heavily. At end-of-life → must be recycled, not thrown in garbage.
11.2 Does Light Travel in a Straight Line? (Rectilinear Propagation of Light)
This is the most important concept of the chapter.
Activity 11.1 → Three matchboxes with holes
| Condition | Observation |
|---|---|
| Holes perfectly aligned | Bright spot visible on screen |
| One box moved slightly | No spot visible |
Inference: Light travels only in a straight line.
Activity 11.2 → Candle flame through pipe
| Pipe type | Observation |
|---|---|
| Straight pipe | Flame clearly visible |
| Bent pipe | Flame not visible |
Inference: Light cannot bend around corners on its own → travels in straight line (rectilinear propagation).
11.3 Shadows
When an opaque object blocks light → dark patch formed behind it = shadow.
- Shadow forms only when light travels in straight line.
- Size of shadow depends on distance between object, light source and screen.
- During solar eclipse → Moon blocks sunlight → shadow falls on Earth.
11.4 Reflection of Light
When light falls on a smooth/shiny surface, it bounces back → reflection.
- Regular reflection: Smooth surface (mirror) → clear image
- Diffused reflection: Rough surface (wall) → no clear image, but object visible
11.5 Images formed by Plane Mirror
- Virtual, erect, same size, laterally inverted, same distance behind mirror as object is in front.
- Lateral inversion → left appears right and vice-versa (AMBULANCE written reversed on ambulances).
Key Takeaways & Exam Points
| Concept | Key Fact |
|---|---|
| Rectilinear propagation | Light always travels in straight line – proved by both activities |
| Luminous objects | Sun, bulb, firefly, candle flame |
| Non-luminous | Moon, table, book, human body |
| Shadow formation | Only when light is blocked by opaque object |
| Plane mirror image | Virtual, erect, laterally inverted, same size & distance |
| LED advantage | Less electricity, brighter, long life, eco-friendly |
One-Page Revision Map
Sources → Luminous (own light) | Non-luminous (reflect)
Travel → Straight line (Activities 11.1 & 11.2)
Shadow → Opaque object blocks light blocked
Reflection → Light bounces back
Plane Mirror → Virtual, erect, laterally inverted
LED → Energy saver, promoted by government
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