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Notes Chapter 11 Class 7 Science Curiosity NCERT

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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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