Lenses

• Lenses refract light
• Concave:

  • middle is thinner than the edges
  • curves inward
  • 'diverging'

  
• Convex:

  • middle is thicker than the edges
  • curves outward
  • 'converging'

  
• Lens Diagram:

  A) Focus

  B) Focal Length

  C) Principal Axis

  
• Ray Diagrams for Convex Lenses:

  • Ray 1 - parallel to the axis, refracting through F
  • Ray 2 - through F, parallel to the axis
  • Ray 3 - through centre of the lens, undeflected

  A) Ray 1

  B) Ray 2

  C) Ray 3

  
• Ray Diagrams for Concave Lenses:

  • Ray 1 - parallel to the axis, refracts through F on object side
  • Ray 2 - through F on opposite side, refracts parallel to axis from lens
  • Ray 3 - through centre of lens undeflected

  A) Ray 1

  B) Ray 2

  C) Ray 3

  
• Images can be formed:

  • upright or inverted
  • magnified or diminished
  • real or virtual
• Real - can be projected onto a screen

  • appears on the other side of the lens
• Virtual - are perceived to be in front of the object

  • appears before the lens
• Magnification = image height/object height