Physics 202, Lecture 24

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Physics 202, Lecture 24

• Todays Topics
• Image Formation
• Real Image, Virtual Image, and No Image
• Ray Diagram
• Images Formed by
• Mirrors (reflection)
• Concave and Convex
• Lenses (refraction)
• Converging and Diverging

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Imaging

• Imaging visible object ? optical device ? image

image lights
optical device
object lights
Image
visible object
Note If image can be formed, only two rays per
point are necessary
Image Aberration Poorly focused imaged points

No Image No point to point correspondence
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Image Properties

• Image properties to be concerned include
• location, real/virtual, reduced/enlarged,
  upright/inverted, similar/distorted,

Real and Virtual Images
Real Image image lights actually pass through
image
Virtual Image image lights appear to have come
from the image

• Real images can be formed on a screen.

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Ray Diagrams

• If image can be formed, only two rays are
  necessary to determine an image point.
• Useful rays
• Object ray pointing to the center (C)
• ? image ray inline with the object ray
• Object ray parallel to principal axis
• ?image ray pointing to a focal point (F)
• Object ray passing through a focal point
• ? image ray parallel to principal axix.

optical device
O
principal axis
F
F
C
I
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Image Formation Equation and Magnification
Parameters p object distance q image
distance h object height h image height M
magnification f focal length
Mirrors and Thin Lenses
If Mlt1 ? Image lt Object If Mgt1 ? Image gt
Object If Mlt0 ? Image ?? Object If Mgt0 ? Image ??
Object
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Image Formed by Flat Mirrors
Parameters p object distance q image
distance h object height himage height M
magnification

• Properties
• Image is virtual and behind the mirror.
• Object distance image distance (pq)
• Lateral magnification M1
• Image is upright (for upright object)
• Image has front/back reversal.

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Image Formed by Convex Mirror
R

• Quiz 1 Is there another convenient ray to use?
• Quiz 2
• Real or virtual?
• Upright or inverted?
• Enlarged or reduced?
• Answer Virtual, upright (Mgt0), reduced (Mlt1)

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Image Formed by Concave Mirrors
Object in front of Mirror real, inverted.
Enlarged or reduced, depending on p.
Object (O) in between F and Mirror virtual,
upright, enlarged
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Image Formed by Refraction
Example looking at a fish
R q - p(n2/n1) M-q/p n2/n1lt1
Closer, not-inverted, reduced, virtual
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Thin Lenses

• Lenses are refractive optical devices with two
  spherical sides.

R1
R2
f2
Thin
F1,F2 Focal points ff1f2 Focal length
f1
fgt0 converging flt0 diverging
Lens makers equation
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Converging and Diverging Lenses
sign convention fgt0
sign convention flt0
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Images Formed by Converging Lens

• Object (O) is in front of F1 real, inverted,
  enlarged or reduced

• Object (O) in between F1 and lens virtual,
  upright, enlarged.

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Images Formed by Diverging Lenses
Images Formed by Diverging Lenses
Images are always virtual, upright, and reduced
Images are always virtual, upright, and reduced
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Sign Conventions