Class 7 Science: Light

• Introduction

  • Straight line travel of light
  • Rectilinear propagation of light
  • Definition of a Ray and a Beam of light

• Reflection of Light

  • Definition: Bouncing back of light from a polished/shiny surface
  • Examples: A shiny spoon, a plane mirror
  • Angle of Incidence equals Angle of Reflection (Basic law)
  • Types of Images:
    • Real Image (can be obtained on a screen)
    • Virtual Image (cannot be obtained on a screen)

• Characteristics of Image by a Plane Mirror

  • Erect (Upright)
  • Virtual
  • Same size as the object
  • Distance of image equals distance of object
  • Lateral Inversion (Left appears right, right appears left)

• Spherical Mirrors

  • Concave Mirror (Curving inward)
    • Forms real and virtual images
    • Used by dentists, in torches, headlights
  • Convex Mirror (Curving outward)
    • Forms diminished and virtual images
    • Used as rear-view mirrors in vehicles

• Lenses

  • Convex Lens (Thicker in the middle, thinner at edges)
    • Converging lens (brings light rays together)
    • Used in magnifying glasses, microscopes
  • Concave Lens (Thinner in the middle, thicker at edges)
    • Diverging lens (spreads light rays apart)
    • Always forms virtual, erect, and diminished images

• Sunlight: White or Colored?

  • Spectrum of white light (7 colors)
  • Rainbow formation in the sky
  • Newton’s Disc experiment (recombining colors to white)
  • Acronym for colors: VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red)