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Images
• Real: light converges to a point.
• Ex. magnifying glass used to start fire.
• Virtual: light diverges (or appears to have diverged) from a point.
• Ex. Any “.” on this screen can be seen anywhere in room.
Animated Mirror Diagrams
• http://www.glenbrook.k12.il.us/gbssci/phys/Class/refln/u13l3d.html
7
Mirror Equations
• relate do, di & f.
• lateral magnification (LM) = hi/ho.
you must learn the sign conventions to use these formulas
fdd io
111
o
i
o
i
d
d
h
hLM
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Ex. Object sits 25cm in front of concave mirror with f = 15cm. Calculate the image distance and magnification. Check with a ray diagram.
14
lens power
• power = 1/(focal-length(meters))
• unit: [D, diopters, 1/m]
• used for corrective lenses
• Ex. near-sighted person P = -5.0Df = 1/P = 1/(-5) = -0.2m = -20cm.
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Summary
• mirror & lens parameters
• ray diagramming, image formation and characterization
• calculation of parameters
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Paraxial Approximation
• Focus isn’t exact for a spherical mirror (but rays near axis focus well)
• Focus is sharp for parabolic mirror (aspheric)
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??do?? #43
• Silvered sphere R = 20cm, f = -10cm
• hi = 1/3 ho
• LM = hi/ho = -di/do = 1/3. -3di = do
• 1/do + 1/di = 1/f
• 1/(-3di) + 1/di = 1/(-10)
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??do?? #67
• f = +10cm lens, what do causes LM = -2.
• LM = hi/ho = -di/do = -2 di = 2do
• 1/do + 1/di = 1/f
• 1/do + 1/2do = 1/10