7 LESSON_Q2

• Refraction


  The phenomenon where light rays change direction when passing from one transparent medium to another
• Normal line


  • A line perpendicular to the boundary between two transparent media at the point where the light ray crosses
  • Used to measure the angles of incidence and refraction
• Angle of incidence


  The angle between the incident ray and the normal line
• Angle of refraction


  The angle between the refracted ray and the normal line
• The angle of incidence is not equal to the angle of refraction in refraction
• Light travels from a medium with lower density to a medium with higher density


  The refracted ray moves closer to the normal line, making the angle of refraction smaller than the angle of incidence
• Light travels from a medium with higher density to a medium with lower density


  The refracted ray moves away from the normal line, making the angle of refraction larger than the angle of incidence
• Lens


  A transparent material shaped to diverge or converge parallel incident light rays
• Convex lens


  • Thick at the center and thinner at the edges
  • Converges parallel light rays to a real focus
• Concave lens


  • Thinnest at the center and thickest at the edges
  • Diverges parallel light rays so they do not meet at a real focus
• Light rays are refracted twice when passing through a lens
• Thin lens approximation


  An approximation technique where light rays are bent only once when passing through a lens, instead of twice
• Thin lens approximation


  1. Draw a lens axis that divides the lens vertically into two equal parts

  2. Draw the incident ray until it reaches this axis before bending it to the focus
• The bending of the light rays in this method is NOT what happens in the real world but it still produces the same effect in terms of the direction of the light rays exiting the lens
• Refraction


  The phenomenon that occurs when light travels across the boundary of two transparent materials
• The angle of incidence is inversely proportional to the angle of refraction
• Refracted ray


  Tends to bend towards the normal line when light travels from a less dense medium to a denser one
• Refracted ray


  Tends to bend away from the normal line when light travels from a denser medium to a less dense medium
• Lens


  A transparent material shaped in a specific way to converge or diverge parallel light rays upon refraction
• Convex lens


  Thinnest at the edges and thickest at the center, converges parallel light rays into a focus
• Concave lens


  Thinnest at the center and thickest at the edges, diverges or scatters parallel light rays
• Convex lenses form real foci, concave lenses form virtual foci
• Important points in a lens setup

  • Focus (F)
  • 2 times the focal length (2F)
  • Vertex (V)
  • Principal axis
  • Lens axis
• Ray diagramming


  1. Always use an arrow to represent the object

  2. Draw the object as upright with its base starting from the principal axis

  3. Draw incident rays from the top of the object/arrow
• 1. F ray


  An incident ray parallel to the principal axis is refracted to pass through the real focus
• V ray


  An incident ray parallel to the principal axis is refracted to align with the virtual focus
• 1. P ray


  An incident ray passing through the real focus is refracted to be parallel to the principal axis
• The P-F ray and V ray are applicable to all situations, the F-P ray is not
• Characteristics of images formed by lenses

  • Location (beyond 2F, at 2F, between 2F and F, at F, between F and V, on same side as object)
  • Orientation (upright or inverted)
  • Size (bigger, smaller, same size as object)
  • Type (real or virtual)
• Image formed by a convex lens when object is at 2F

  • Location - at 2F
  • Orientation - inverted
  • Size - same size
  • Type - real
• Image formed by a concave lens when object is between F and V

  • Location - same side as object, between F and V
  • Orientation - upright
  • Size - smaller
  • Type - virtual
• Ray diagramming for lenses

  1. Draw incident rays

  2. Draw refracted rays

  3. Determine image formation
• Rays used in ray diagramming

  • Principal ray (parallel to principal axis, passes through focus)
  • Vertex ray (passes through lens vertex, not refracted)
  • Focus-principal ray (passes through focus on one side, parallel to principal axis on other side)
• Possible locations of object relative to lens

  • Between focus (F) and vertex (V)
  • At focus (F)
  • Between 2F and F
  • At 2F
  • Beyond 2F
• Image orientation


  Upright or inverted
• Image size


  Smaller, same size, or larger than object
• Image type


  Real or virtual
• Convex lens


  Refracts parallel light rays to converge at a real focus
• Concave lens


  Refracts parallel light rays to diverge
• Ray diagramming is a technique to determine image qualities