I. Key Terms and Phrases

geometrical optics the study of the reflection and refraction of light under the ray approximation

light ray a representation of the straight-line propagation of light

law of reflection the fact that the angle of incidence equals the angle of reflection for light reflecting from a smooth surface

object the source of the light from which an image will be formed by a mirror or a lens

image the representation of an object resulting from the convergence, or apparent convergence, of light rays coming from the object by reflection or refraction

upright image an image that is right-side-up with respect to the object

inverted image an image that is upside-down with respect to the object

magnification ratio of the image height to the object height

focal point the point on the principal axis at which incident rays that are parallel to the principal axis (or their extensions) will intersect after reflection or refraction

focal length the distance of the focal point from the mirror or lens

real image an image formed by the intersection of light rays

virtual image an image formed by the intersection of extensions of light rays into a region where no light is actually present

refraction the phenomenon that the direction of propagation of light generally changes when it crosses the boundary between two media

index of refraction the ratio of the speed of light in vacuum to the speed of light in a medium

Snell's law relates the angle of incidence to the angle of refraction

total internal reflection a phenomenon that occurs at incident angles greater than that for which the angle of refraction is 90°

Brewster's angle the angle at which refracted light is completely polarized

dispersion the spreading of light of different frequencies due to the fact that the index of refraction is frequency dependent

II. Important Equations

Name/Topic	Equation	Explanation
reflection		The law of reflection.
spherical mirrors		The mirror equation.
magnification		This expression for the magnification applies to both mirrors and lenses.
refraction		The definition of the index of refraction.
refraction		Snell's law, which describes the refraction of light.
thin lenses		The thin-lens equation.

III. Know Your Units

Quantity	Dimension	SI Unit
magnification (m)	dimensionless	---
index of refraction (n)	dimensionless	---

IV. Additional Tools

Recording Calculator
This is a 'printing' scientific calculator. It allows you to check your calculations by reviewing your work.

Scientific Calculator
This is a standard scientific calculator.

Graphing Calculator
This is a simple graphing calculator, the JavaScript resource of the month for several months at Developer.com.

Physical Constants
This is a searchable database of physical constants.

Conversion Engine
This conversion factor tool gets almost 1000 hits a day and has been featured by Microsoft.

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