Light, Shadows and Reflections

Class 6 Science | CBSE NCERT Curriculum

This chapter explains luminous and non-luminous objects, transparent, translucent and opaque materials, formation of shadows, pinhole camera, reflection of light from mirrors, and rectilinear propagation of light.

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Quick Revision: Light, Shadows and Reflections

  • Luminous Objects: Objects that emit their own light (Sun, stars, torch, firefly, candle flame).
  • Non-luminous Objects: Objects that do not emit light; they become visible when light falls on them (chair, book, moon).
  • Transparent: Allow light to pass through completely (glass, air, water).
  • Translucent: Allow light to pass partially (tracing paper, butter paper, fog).
  • Opaque: Do not allow light to pass through (wood, metal, cardboard).
  • Shadow Formation: Requires a light source, an opaque object, and a screen. Shadows are always dark, formed opposite to light source.
  • Properties of Shadows: Same colour as object doesn't affect shadow colour; size changes with distance from light source; shape can vary with object orientation.
  • Pinhole Camera: Simple camera using light travelling in straight line; produces inverted (upside down) images.
  • Rectilinear Propagation: Light travels in straight lines. Demonstrated by pipe/tube experiment.
  • Reflection: Bouncing back of light from a smooth surface like a mirror.
  • Mirror Reflections: Reverse left and right; image appears as if right hand is left hand.
  • Periscope: Device using two mirrors to see around corners.
  • Natural Pinhole Camera: Gaps between tree leaves act as pinholes, creating Sun images on ground.

Chapter Summary: Light, Shadows and Reflections

Light is essential for us to see objects. Luminous objects emit their own light (Sun, torch, firefly), while non-luminous objects become visible when light falls on them. Materials can be transparent (allow light to pass fully), translucent (partially), or opaque (no light passes). Shadows are formed when an opaque object blocks light, requiring a light source, an opaque object, and a screen. Light travels in straight lines (rectilinear propagation), demonstrated by the pipe experiment.

A pinhole camera uses this principle to form inverted images. Natural pinhole cameras occur under trees with dense foliage - gaps between leaves create circular images of the Sun. Mirrors reflect light, changing its direction. In a mirror, left and right appear reversed. A periscope uses two mirrors to see around corners. Understanding these principles helps explain everyday phenomena like shadows, reflections, and images.