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Ray model
A model that assumes light travels in rays
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Geometric optics
The subject of light acting as a ray with reflection, refraction, and the formation of images by mirrors and lenses
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Angle of incidence
The angle an incident ray makes with the normal (perpendicular) to the surface
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Angle of reflection
The angle the reflected ray makes with the normal
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Law of reflection
The angle of reflection equals the angle of incidence
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Diffuse reflection
When light hits a rough surface and is reflected in many directions
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Specular reflection
When light hits a smooth surface and reflects in one direction
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Image
Picture made by reflected light
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Virtual image
An optical image formed by the apparent divergence of rays from a point, rather than their actual divergence from a point (when it doesn't actually focus, but our brain connects the dots)
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Real image
An optical image formed by the actual divergence of rays from a point (never upright - opposite of virtual)
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Convex
Spherical mirror with which the reflection takes place on the outer surface so that the center of the mirror surface bulges out
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Concave
A mirror where the reflecting surface is on the inner surface so that the center shrinks away (like a cave)
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Focus
Where reflected parallel rays cross each other
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Principal axis
The straight line perpendicular to the curved surface at it's center
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Focal point
- Where incident parallel rays come to a focus after reflection
- Also the image point for an object infinitely far away along the principal axis
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Focal length
Distance between the focal point and the center of the mirror
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Paraxial rays
Rays that make a small angle with the principal axis, so that they reflect at F
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Spherical abberation
When rays from an image pass through the outer regions of the lens or mirror and are brought to a focus at a different point from those that pass through the center of the lens.
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Do
Object distance, distance of the object from the center of the mirror (x value)
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Di
Image distance, distance of the image from the center of the mirror (x value)
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Ho
Object height, height of the object from the center of the mirror (y value)
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Hi
Image height, height of the image from the center of the mirror (y value)
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Mirror equation
- 1/do + 1/di = 1/f
- Where f is the focus, or r/2.
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Magnification
"m", the height of the image divided by the hight of the object (hi/ho). This is also (-di/do).
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Index of refraction
The ratio of the speed of light in a vacuum to the speed v in a given material. Denoted as n.
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Refraction
When a ray of light changes direction as it enters a new medium
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Angle of refraction
The angle the refracted ray makes with the normal to the surface
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Snell's law
The angle of refraction depends on the speed of light in the two media and on the incident angle, also written as n[1]sint[1] = n[2]sint[2].
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Law of refraction
Snell's law, or n[1]sint[1] = n[2]sint[2]
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Critical angle
The incident angle at which the refracted ray would skim the surface, meaning the angle of refraction would be 90 degrees.
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Total internal reflection
- When there is no refracted ray, all of the light is reflected
- Only occurs when the second medium has a lower index of refraction
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Fiber optics
Total internal reflection used with tiny fibers as thin as a few micrometers in diameter
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Converging lens
A lens that is thicker in the center than at the edges, which will make parallel rays converge to a point
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Diverging lens
A lens that is thinner in the center than at the edges, and make parallel light diverge
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Thin lens equation
Same as the mirror equation, 1/do = 1/di = 1/f
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Sign conventions
- Focal length: pos for converging, neg for diverging
- Di: pos if image is on opposite side of the lens, neg if same side
- Hi: pos if upright, neg if inverted
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