Optics The Swing, Pierre- Auguste Renoir Oil on canvas, 1876 How does this painting give evidence that light carries information? A Bar at the Folies-Bergère, Édouard Manet Oil on canvas, 1882 What distortions can you find in this painting that give it an unusual “feel?” click for applet
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Optics
The Swing, Pierre-Auguste Renoir Oil on canvas, 1876
How does this painting give evidence that light carries information?
A Bar at the Folies-Bergère, Édouard Manet Oil on canvas, 1882
What distortions can you find in this painting that give it an unusual “feel?”
click forapplet
Mirrors and Reflection of Light
Plane Mirror Conclusions
Apparent path length of light equals actual path length of light
Image size is the same as the object, therefore heights are equal, ho = hi
Image orientation seems inverted horizontally (left/right), but is not.
Incident angle equals reflected angle. Law of Reflection means θi = θr
Image location (or distance) equals object distance, do = di
Image type is virtual. Rays of light appear to diverge from image point, and cannot physically converge onto a surface.
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ho hi
do di
mirror
objecteye
image
eye
θr θi
Virtual Images
A virtual image is formed when rays appear to diverge from a point.
For a mirror, a virtual image will form behind the mirror, and it is upright.
A virtual image cannot be cast onto a surface, but is seen in with the eye.
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Reflection of Light
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Light always obeys the Law of Reflection but the surface irregularities (compared to the wavelength of light) determine whether the reflection is specular or diffuse.
Multiple mirrors produce many reflections!
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Real Images
A real image is formed when rays actually converge to an point.
For a mirror, a real image will form in front of the mirror, and it is inverted.
A real image often appears on a surface, and then seen with the eye, but can also be viewed in a mirror.(A virtual image is only seen in a mirror)
real image
virtualimage
Curved Mirrors
CONCAVE MIRROR CONVEX MIRROR
Light that reflects off a spherical mirror will not focus clearly.
A smaller mirror, or a parabolic mirror, avoids spherical aberration.
SPHERICAL MIRROR PARABOLIC MIRROR
Some variablesf = focal lengthF = focus (or focal pt)r = radius of curvatureC = center of curvature
Ray Diagrams - Mirrors
Principal RaysAn incident ray parallel to the principal axis, reflects back through, or from, the focal point.
An incident ray through, from, or towards the focal point, reflects back parallel to the principal axis.
An incident ray through, from, or towards the center of curvature, reflects back along itself.
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Mirror & Magnification Equation, Sign Conventions
Note: magnification sign does not indicate image size. If |M| < 1 image is smaller, |M| > 1 image is larger.
Sign conventions Positive Negative
object distance
image distance
focal length
mirror type
image height
magnification
REAL object, in front of mirror VIRTUAL object
REAL image, in front of mirror VIRTUAL image, behind mirror
REAL focus, in front of mirror VIRTUAL focus, behind mirror
CONVERGING or CONCAVE DIVERGING or CONVEX
UPRIGHT INVERTED
UPRIGHT INVERTED
1
f=
1do
+1di
M =−dido
=hiho
Type Size Orientation Location
PLANE
DIVERGING(convex)
MIRROR
CONVERGING(concave)
ImageObjectPosition
anywhere virtual same upright behind mirror| di | = do
between mirror and F virtual larger upright
behind mirror| di | > do
betweenF and C real larger inverted
in front, beyond C
di > do
at C real same inverted in front, at Cdi = do
beyond C real smaller invertedin front, btw F & C
di < do
anywhere virtual smaller uprightbehind mirror
| di | < do
Mirror Summary
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