Reflection

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Reflection

• Regular reflection occurs when parallel light
  rays strike a smooth surface and reflect in the
  same direction.

• Diffuse reflection occurs when light rays reflect
  off a rough surface and are scattered in
  different directions.

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Reflection

• The Law of Reflection When light reflects off a
  surface, the angle of incidence is always equal
  to the angle of reflection.
• Where are plane mirrors used?

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Plane mirrors

• A virtual image is any image formed by rays that
  do not actually pass through the location of the
  image. Light rays are not coming from where the
  image appears to be.

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Curved Mirrors

• Concave and convex
• Curved mirrors obey the law of reflection.

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Concave vs. Convex mirrors
When rays that are parallel to the principal axis
strike a concave mirror, they are ALL reflected
through the same point, called the focal point.
If several groups of parallel rays are reflected
by a concave mirror, each group converges at a
point.
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Concave vs. Convex mirrors

• Concave mirrors are also called converging
  mirrors
• Concave mirrors are designed to collect light and
  bring it to a single point
• Examples Cosmetic mirrors to produce an enlarged
  image, Telescopes to collect light from a
  distance source and focus it for viewing
• Concave mirrors can also be used to send out
  beams of light rays
• Examples flashlights, car headlights, dental
  examination lights

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Concave vs. Convex mirrors
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Concave vs. Convex mirrors

• Convex mirrors are also called diverging mirrors
• Convex mirrors spread out rays
• They allow you to view a large region that you
  could not see with a plane mirror of the same
  size
• Examples Store security, parking lot safety,
  side-view mirrors, camera phones

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Curved mirror definitions

• When parallel light rays strike a curved mirror,
  the reflected rays eventually meet at a common
  point. The point where the light rays meet, or
  appear to meet, is called the focal point, F.
• The middle of a curved mirror is the vertex. The
  principal axis is an imaginary line draw through
  the vertex.
• The distance from the vertex to the focal point
  is the focal length, f.
• The center of curvature, C, is the center of the
  circle that would be formed if you extended the
  curve of the mirror.

The focal point is half way between the center of
curvature and the vertex.
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Finding the image

• Each time you find the image, you must determine
  the following
• Size Is it smaller, bigger, or the same size as
  the object?
• Attitude Is it upright or inverted?
• Location Is it behind or in front of the mirror?
• Type Is it real of virtual?

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Real vs. Virtual

• A real image is formed by light rays that
  converge at the location of the image.
• A real image can be projected onto a screen If
  you place a piece of paper at the spot where a
  real image forms, a focused image will appear on
  the piece of paper.
• A virtual image is any image formed by rays that
  do not actually pass through the location of the
  image.
• Light rays are not coming from where the image
  appears to be.
• Unlike a real image, a virtual image cannot be
  projected onto a screen.

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Drawing a CONCAVE MIRROR ray diagram

• (Converging mirror)
• Note Show real rays using solid lines and
  virtual rays using dashed-lines.
• Ray 1 parallel from a point on the object to the
  principal axis (Rays that are parallel to the
  principal axis will reflect through the focal
  point on a concave mirror.)

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Ray 2 from a point on the object through the
focal point. (Rays that pass through the focal
point on a concave mirror will be reflected back
parallel to the principal axis.)
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Ray 3 Draw a line from the same point on the
object through the center of curvature. When the
ray hits the mirror, it will reflect back on
itself. This line determines the quality of the
mirror.Draw the image where the rays
intersect.
Size Smaller Attitude Inverted Location In
front Type Real
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Complete the following table
LOCATION OF OBJECT SIZE OF IMAGE ATTITUDE OF IMAGE LOCATION OF IMAGE TYPE OF IMAGE
More than two focal lengths away from mirror   Smaller Inverted In front Real
Between one and two focal lengths away from the mirror        
Object is at the focal point            
Object is between the mirror and the focal point          
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Drawing a Concave Mirror Ray Diagram Summary

• Ray 1 parallel from a point on the object to the
  principal axis (Rays that are parallel to the
  principal axis will reflect through the focal
  point on a concave mirror.)
• Ray 2 from a point on the object through the
  focal point. (Rays that pass through the focal
  point on a concave mirror will be reflected back
  parallel to the principal axis.)
• Ray 3 Draw a line from the same point on the
  object through the center of curvature. When the
  ray hits the mirror, it will reflect back on
  itself. This line determines the quality of the
  mirror.
• Draw the image where the rays intersect.

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Object is between one and two focal lengths
Size Larger Attitude Inverted Location In
front Type Real
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Object is at the focal point
No Image Formed
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Object is between mirror and focal point
Size Larger Attitude Upright Location
Behind Type Virtual
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Magnification

• One use of concave mirrors is magnification.
• Magnification How large or small an image is
  compared to with the object.

 
 
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Using the formula

• Distances are positive if they are in front of
  the mirror, and negative if they are behind the
  mirror.
• Positive heights are above the principle axis,
  and negative heights are below the principle
  axis.
• Positive magnifications are above the principle
  axis, and negative magnifications are below the
  principle axis
• If the image is bigger than the object, then the
  magnification will be greater than 1.
• If the image is smaller than the object, then the
  magnification will be less than 1.

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Convex mirrors (Diverging)

• Instead of collecting light rays, a convex mirror
  spreads out the rays.
• Drawing a convex ray diagram
• Ray 1 from a point on the ray parallel to the
  principal axis (Any ray that is parallel to the
  principal axis will appear to have originated
  from the focal point.)
• Ray 2 from a point on the object toward the
  focal point (Any ray that is directed at the
  focal point on a diverging mirror will be
  reflected back parallel to the principal axis.)
• Draw the virtual image where the rays appear to
  intersect.
• WHAT ARE THE PROPERTIES OF THE IMAGE PRODUCED?

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Ray 1 from a point on the ray parallel to the
principal axis (Any ray that is parallel to the
principal axis will appear to have originated
from the focal point.)
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Ray 2 from a point on the object toward the
focal point (Any ray that is directed at the
focal point on a diverging mirror will be
reflected back parallel to the principal axis.)
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Draw the virtual image where the rays appear to
intersect.
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Mirror Equation

• Rules
• Concave mirrors have positive focal length and
  convex mirrors have negative focal length
• Distances are positive if they are in front of
  the mirror, and negative if they are behind the
  mirror.
• All measurements are made along the principal
  axis from the surface of the mirror.

 
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References

• Pearson Investigating Science 10
• http//www.blueskiesandyellowdogs.com/2010/08/17/w
  hat-i-love-to-see-most-in-my-rear-view-mirror/
• http//www.sayulitalife.com/dentalsayulita
• http//www.math.ubc.ca/cass/courses/m309-01a/chu/
  Fundamentals/reflection.htm
• http//www.bnl.gov/slc/DiscoveryActivitiesSLC/Mirr
  orMagic.asp
• http//www.bnl.gov/bnlweb/schoolprograms.html
• http//shiratdevorah.blogspot.ca/2010/10/rainbow-c
  ovenant.html
• http//epod.usra.edu/blog/2010/03/highway-mirage.h
  tml