# Optics Formulas

## Equations for Geometrical Optics

 Law of Reflection States that the angle of incidence () is equal to the angle of reflection () as measured from the normal to the reflecting surface.
 Snell's Law Alternate Form Gives the relationship between angles of incidence () and angles of refraction () for a wave impinging on an interface between two media with different indices of refraction (, )
 Index of Refraction The index of refraction () is a ratio of speeds that compares the speed of light in a medium () to the speed of light in a vacuum (). The ratio can also be defined in terms of the wavelength () of light in different materials.
 Critical Angle The critical angle ()is the certain angle of incidence at a boundary between two materials where the angle of refraction equals 90°. This formula is used to calculate that angle, and works only if > . Note: if the second medium is air or a vacuum, then is approximately 1.

## Equations for Mirrors and Lenses

 Magnification Factor for Plane Mirrors Magnification Factor for Spherical Mirrors and Lenses Focal Length for a Spherical Mirror Spherical Mirror Equation Alternate Form Thin Lens Equation Alternate Form Note: the equations for spherical mirrors and thin lenses are the same.

## Equations for Young's Double-Slit Experiment

 Path Difference for Constructive Interference Path Difference for Destructive Interference Bright Fringe Condition (double slit interference) Wavelength (double slit interference) Width of Bright Fringe (double slit interference) Nonreflecting Film Thickness (minimum)