Light: Shadows and Reflections
1. Sources of Light
- Luminous Objects: Produce their own light (e.g., Sun, stars, fireflies, bulbs).
- Non-Luminous Objects: Reflect light from other sources (e.g., Moon reflects sunlight).
- Natural Sources: Sun, stars, lightning.
- Artificial Sources: Fire, candles, LED bulbs.
- LED Lamps: Energy-efficient, long-lasting, eco-friendly; must be recycled.
2. Light Travels in a Straight Line
Light moves in a straight line, proven by:
- Matchbox Activity: Light passes through aligned holes; misaligned holes block it.
- Pipe Activity: Candle flame visible through straight pipe, not bent pipe.
- Laser Beam: Stays straight in water, confirming light’s linear path.
3. Light and Materials
- Transparent: Light passes fully (e.g., glass).
- Translucent: Light passes partially (e.g., tracing paper).
- Opaque: Light is blocked (e.g., cardboard).
- Activity: Test materials with a torch to observe light passage.
4. Shadow Formation
- Shadow: Dark patch formed when an opaque object blocks light.
- Requirements: Light source, opaque object, screen (e.g., wall).
Observations:
- Opaque objects form darker shadows.
- Translucent objects form lighter shadows.
- Shadow size/shape depends on object’s position.
- Object color doesn’t change shadow color.
5. Reflection of Light
- Reflection: Light bounces off shiny surfaces (e.g., mirrors).
- Activity: Use a mirror to redirect sunlight; observe light changing direction.
- Plane Mirror: Reflects light to form images.
6. Images in a Plane Mirror
Image Properties:
- Same size as the object.
- Upright (erect).
- Virtual (cannot be caught on a screen).
- Laterally inverted (left appears right, e.g., “AMBULANCE” text).
Activity: Observe image distance and lateral inversion in a mirror.
7. Pinhole Camera
- Pinhole Camera: Forms an image through a tiny hole.
- Image: Inverted (upside down), shows object’s colors.
- Construction: Use cardboard boxes, a pinhole, and a translucent screen.
8. Useful Items
- Periscope: Two mirrors at 45° angles to see around corners (used in submarines).
- Kaleidoscope: Three mirrors in a triangle create colorful patterns (used by designers).
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