photo:optics
optics
see also:
see web articles:
reflection
laws of reflection:
the angle of incidence = the angle of reflection
the incident ray, the reflected ray & the normal to the surface lie in the same plane
spherical mirrors:
principal focus is the convergence point for rays parallel to & close to the principal axis of the mirror, and is located halfway between the mirror & its centre of curvature, ie. focal length = radius/2
the mirror equation:
magnification = q/p;
refraction
speed of light depends on the medium in which it travels (water = 3/4 that in air)
refraction (change of direction) occurs when light passes from a medium of one density to a medium of another density
a material of lesser speed is called “optically more dense”
refractivity of a medium:
optical dispersion:
the variation of the index of refraction with the wavelength of light is called the optical dispersion of a substance
short wavelengths are refracted more than long wavelengths
substances with high optical dispersion, usually also have a high index of refraction (eg. diamond)
Snell's law:
for a given wavelength & a pair of substances, the ratio of the sine of the angle of incidence (i) to the sine of the angle of refraction ® is constant
abs.index medium 1 * sin i = abs.index medium 2 * sin r
examples:
underwater viewing:
mirages:
on still sunny days, there may be a layer of hot, expanded air in contact with the heated ground in which light travels faster, thus light entering it obliquely will be refracted upwards resulting in observer seeing inverted images of distant objects suggestive of reflections in a smooth pool of water. These are often seen on highways.
looming:
when the air near the ground is cooler than the upper strata (eg. over snow or over water), rays of light are deviated downward, thus one may see an image of a ship above the ship itself, or the curvature may allow one to see objects below the horizon.
total internal reflection:
for light passing from a medium to a less dense medium, there is an incident angle whereby refraction will no longer occur & the light is internally reflected instead, this occurs as the angle of refraction approaches 90deg. (when sin r = 1)
thus critical angle of incidence (ic) can be determined from sin ic = abs.index medium 2 / abs.index medium 1
therefore, for water/air interface when viewed from under water, the critical angle is 48deg.
spherical surfaces:
thin lenses:
aberrations:
photo/optics.txt · Last modified: 2019/07/07 08:36 by gary1