Geometric Optics

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Geometric Optics
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• Uses wave model of light to explain properties
  such as reflection and refraction
• Assumptions of geometric optics
• - light travels in straight lines
• - ray path taken by light

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Pinhole Camera

• Simplest version of a camera consisting of a box
  with a small opening
• Light ray passing from the top of an object go
  through the hole and hit the back of the box
• Light ray passing from the bottom of the object
  go through the hole and hit the back

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Image Characteristics

• Real Image can be formed on a screen not
  virtual
• Image smaller than object
• Image is inverted
• If photographic film placed on the back of the
  box, picture is permanent

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Equation

• hi di
• ho do
• hi - height of image
• di distance of image
• ho height of object
• do distance of object

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Magnification (M)

• M hi ho
• If M gt 1, image is enlarged
• If M lt 1, image is reduced

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Example

•  

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Reflection

• When light rays hit an opaque (not transparent)
  surface, they are reflected
• Law of Reflection
• angle of incidence
• angle of reflection
• i r

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normal
i
r
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Diffuse Reflection

• When light reflected from uneven surfaces reflect
  in many directions (no image can form)

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Images

• When parallel rays of light are reflected
  parallel, an image can form
• Image formed is virtual (not real) and appears at
  the same distance behind the mirror as the object
  is in front (di do)
• Image formed is the same height as the object (hi
  ho)

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Brains Role

• Light ray from the object hits the mirror and
  reflects to the eye
• Brain assumes that light travels in a straight
  line so we believe the reflected light originated
  somewhere behind the mirror

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Image Characteristics

• Virtual
• Same size
• Erect
• Laterally inverted