Mirrors and Lenses

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					            Mirrors, Lenses, and the Eye
3
      Light Rays
      Mirrors
• A mirror is any surface that produces a
  regular reflection.
      Plane Mirrors
• A flat smooth mirror is a plane mirror.
            Mirrors, Lenses, and the Eye
3
      Plane Mirrors
• Light rays from a light
  source strike you.
• Every point that is struck
  by the light rays reflects
  these rays so they travel
  outward in all directions.
• Light rays are reflected
  from the mirror back to
  your eyes.
             Mirrors, Lenses, and the Eye
3
       Virtual and Real Images
• Plane mirrors always form virtual images.
• If light rays from an object pass through
  the location of the image, the image is
  called the real image.
• If the surface of a
  mirror is curved
  inward, it is called a
  concave mirror.
            Mirrors, Lenses, and the Eye
3
      Virtual and Real Images
• The image formed by a concave mirror
  depends on the location of the object relative
  to the focal point.
            Mirrors, Lenses, and the Eye
3
      Virtual and Real Images
• An object between one and two focal lengths
  from a concave mirror is real, inverted, and
  larger than the object.
• An object closer than one focal length from a
  concave mirror produces a virtual image that
  is upright and larger than the object.
            Mirrors, Lenses, and the Eye
3
      Convex Mirrors
• A mirror that curves outward like the back
  of a spoon is called a convex mirror.
• Reflected rays diverge and never meet,
  so a convex mirror
  forms only a
  virtual image.
• The image also
  is upright and
  smaller than the
  actual object is.
            Mirrors, Lenses, and the Eye
3
      Lenses
• A lens is a transparent object with at
  least one curved surface that causes
  light rays to refract.
      Convex Lenses
• A convex lens is thicker in the middle
  than at the edges.
            Mirrors, Lenses, and the Eye
3
      Convex Lenses
• Light rays are refracted toward
  the center of the lens.
• All light rays
  are refracted
  so they pass
  through a
  single point,
  which is the
  focal point of
  the lens.
            Mirrors, Lenses, and the Eye
3
      Convex Lenses
• Lenses with flatter sides have longer focal
  lengths.
            Mirrors, Lenses, and the Eye
3
      Concave Lenses
• A concave lens is thinner in the middle
  and thicker at the edges.
• Light rays that pass through a concave
  lens bend away from the optical axis.
            Mirrors, Lenses, and the Eye
3
      The Human Eye
• Light enters your eye through a transparent
  covering on your eyeball called the cornea.
• The cornea
  causes light
  rays to bend
  so that they
  converge.
• Light then
  passes through
  the pupil.
            Mirrors, Lenses, and the Eye
3
      The Human Eye
• Behind the pupil is a flexible convex lens.
• The retina is the inner lining of your eye,
  containing
  light sensitive
  cells that
  convert an
  image into
  electrical
  signals.
            Mirrors, Lenses, and the Eye
3
      Brightness and Intensity
• The human eye can adjust to the brightness
  of the light that strikes it.
• Light intensity is the amount of light energy
  that strikes a certain area each second.
• Brightness is the human perception of light
  intensity.
• Eyes respond to bright light by decreasing the
  size of your pupil.
            Mirrors, Lenses, and the Eye
3
      Correcting Vision Problems
• If you can see distant objects clearly but can’t
  bring nearby objects into focus, then you are
  farsighted.
            Mirrors, Lenses, and the Eye
3
      Correcting Vision Problems
• The eyeball might be too short or the lens
  isn’t curved enough to form a sharp image
  of nearby objects on the retina.
            Mirrors, Lenses, and the Eye
3
      Nearsightedness
• Eyes cannot form a sharp image on the
  retina of an object that is far away.
• The image is formed in front of the retina.
                Section Check
3
      Question 1
A __________ mirror curves inward.


A. concave
B. convex
C. obtuse
D. plane



                                FL: SC.H.3.4.6
                 Section Check
3
      Answer
The answer is A. A concave mirror curves
inward and forms a real image. A convex
mirror curves outward and forms a virtual
image.




                                  FL: SC.H.3.4.6
                  Section Check
3
       Question 2
What type of lens refracts light rays away from
the optical axis?


       Answer
Concave lenses are thicker at the edges and
refract light rays away from the optical axis.



                                    FL: SC.H.3.4.6
                  Section Check
3
       Question 3
In nearsightedness, the image forms _______
the retina and a _______ lens can be used to
correct it.

A. behind, concave
B. behind, convex
C. in front of, concave
D. in front of, convex

                                  FL: SC.H.3.4.6
                 Section Check
3
      Answer
The answer is C. The image forms in front of
the retina and a concave lens corrects it.




                                  FL: SC.H.3.4.6

				
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posted:2/10/2012
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