Download Reflection - E. R. Greenman

REFLECTION
Physics Chapter 18a
Law of Reflection
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Angle of incidence equals angle of reflection
Reflection
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Change in direction of wave at interface between two
media
Reflecting surface smoothness controls type of reflection
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Specular: smooth surface, forms good image
Diffuse: rough surface, does not form good image
Reflections
Example
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The angle of incidence of a light ray is 42o. What are:
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The angle of reflection
The angle the incident ray makes with the mirror
The angle between the incident ray and the reflected ray
Plane Mirror
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Flat mirror
Forms a virtual image at the same distance that the
object is
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Virtual image is upright
Mirror equation: 1/p + 1/q = 1/f
p=object distance
q=image distance
f=focal length
Plane Mirror
Concave Mirror
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Concave mirror is curved away from observer
Mirror reference points:
 Optical axis
 Normal at center of mirror
 Also called principal axis
 Focal point
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Point on optical axis where every reflected ray
passes through
Focal length: distance from mirror to focal point
(along optical axis)
Concave Mirrors
• Reflections:
• Rays parallel to principal axis reflect through
focal point
• Rays through focal point reflect parallel to
principal axis
• Rays through center (along principal axis)
reflect back along same path
How do we find where an image is?
• Draw carefully!!
How do we find where an image is?
• Draw carefully!!
How do we find where an image is?
• Draw carefully!!