LENSES

• Spherical Lens - A piece of glass or transparent material that has at least one spherical surface.
• A Spherical Lens may be:

  • Convex Lens
  • Concave Lens
• Lenses that are thicker at the middle than the edges are called Convex Lenses
• Lenses that are thicker at the edges than the middle are called Concave Lenses
• Convex lenses are used to correct farsightedness
• Concave lenses are used to correct nearsightedness
• Convex lenses are converging lenses
• Concave Lenses are diverging lenses
• What are these lenses?

  Concave Lenses

  
• What are these lenses?

  Convex Lenses

  
• When a beam of parallel rays falls on a convex lens, the rays are refracted and converge at a point called Principal Focus (F)
• When a beam of parallel rays falls on a convex lens, the rays are refracted and converge at a point called Principal Focus (F)
• Parallel rays falling upon a concave lens will spread out.
• When extended, the refracted rays will appear to come from a point in front of the lens. This is considered the principal focus of the concave lens.
• The Focal Length (f) is the distance from the optical center of the lens to the principal focus.
• How many focal points are in a lens?

  2 (number)