Mirrors

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Chapter 18-1

• Mirrors

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Plane Mirror

• a flat, smooth surface
• light is reflected by regular reflection rather
  than by diffuse reflection
• Light rays are reflected with equal angles of
  incidence and reflection.

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Plane Mirror

• Produces a virtual image which appears to be an
  equal distance behind the mirror. With a virtual
  image, the light rays do not actually converge on
  the point where the image appears.
• The object and the image have the same size.
• They are pointing in the same direction, so the
  image is an erect image.
• Left and right are reversed which is to say the
  front and back of the image are reversed.

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If you blink your right eye, your mirror image
left eye blinks back at you
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Concave Mirrors

• A concave mirror reflects light from its inner,
  (caved in) surface.
• The principal axis is the straight line
  perpendicular to the surface of the mirror at its
  center.
• The focal point
• is the point where all rays parallel to the
  principal axis meet.
• It is half the distance between the mirror and
  the center of curvature (C).
• If you point the principal axis of a concave
  mirror at the sun, all the rays (which are
  parallel to each otherat infinity) will be
  reflected through the focus
• The distance from the focal point to the mirror
  along the principal axis is the focal length, f,
  of the mirror.

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Real vs Virtual Images

• Real Image
• the rays actually converge and pass through the
  image
• it can be seen on a piece of paper or screen
• Virtual Image
• The rays do not converge at the location of the
  virtual image
• The virtual image cannot be projected on a screen

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How to draw Ray Diagrams

• Draw the mirror, principal axis, a vertical line
  where the principal axis touches the mirror, the
  image, the focal point (F) and the center of
  curvature (C).

Ray 1 (the parallel ray) is from the object to
the mirror parallel to the principal axis. The
reflected ray goes through the focal point Ray 2
(the focus ray) is from the object through the
focal point. The reflected ray is parallel to
the principal axis Where Ray 1 and Ray 2
intersect is the location of the image.
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Possible scenarios for Concave Mirrors
Object Image
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Lens/mirror equation If I do I die.

• f focal length
• do distance of object from mirror
• di distance of image from mirror

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Magnification

• the ratio of the size of the image, hi ,
• to the size of the object, ho

or
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b. How high is the image?
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Virtual Images Formed by Concave Mirrors
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Image defect in Concave Mirrors

• Spherical aberration
• Parallel Incident Light from outer edge of
  spherical mirror fails to focus at a point
• Fix Parabolic mirror

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Convex Mirrors

• A convex mirror is a spherical mirror that
  reflects light from its outer surface.
• Rays reflected from a convex mirror always
  diverge.
• Focal length, f, is a negative number (because F
  is behind the mirror)
• di is negative because the image is behind the
  mirror

• Convex mirrors do not form real images.
• Images are reduced in size and so appear far away
• Fisheye lens the image is small (reduced) but
  wide ranging
• (enlarged) field of view upright image,
  virtual, reduced
• (images seem farther away)
• Good for security mirrors rearview mirrors in
  cars

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Problem from Opening Page of Chap 18 in Textbook

• Four Butterflies but only one is real.
• Identify the images and the shape of lenses that
  produced them

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End 18-1