Optics Mirror and Lenses

Pages: 2 (390 words) Published: March 25, 2012
Mirrors and Lenses
We describe the path of light as straight-line rays
Reflection off a flat surface follows a simple rule:
angle in (incidence) equals angle out (reflection)
angles measured from surface “normal” (perpendicular)
Reflection Vocabulary
Real Image –
Image is made from “real” light rays that converge at a real focal point so the image is REAL Can be projected onto a screen because light actually passes through the point where the image appears Always inverted

Reflection Vocabulary
Virtual Image–
“Not Real” because it cannot be projected
Image only seems to be there!
Virtual Images in Plane Mirrors
Hall Mirror
Useful to think in terms of images
Curved mirrors
What if the mirror isn’t flat?
light still follows the same rules, with local surface normal Parabolic mirrors have exact focus
used in telescopes, backyard satellite dishes, etc.
also forms virtual image
Concave Mirrors
Curves inward
May be real or virtual image
For a real object between f and the mirror, a virtual image is formed behind the mirror. The image is upright and larger than the object.

Convex Mirrors

Curves outward
Reduces images
Virtual images
Use: Rear view mirrors, store security…
Light also goes through some things
glass, water, eyeball, air
The presence of material slows light’s progress
interactions with electrical properties of atoms
The “light slowing factor” is called the index of refraction glass has n = 1.52, meaning that light travels about 1.5 times slower in glass than in vacuum water has n = 1.33
air has n = 1.00028
vacuum is n = 1.00000 (speed of light at full capacity)
Refraction at a plane surface
Light bends at interface between refractive indices
bends more the larger the difference in refractive index
Convex Lenses
Thicker in the center than edges.
Lens that converges (brings together) light rays.
Forms real images and virtual images...
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