Topic: light

topics > Group: science

atoms and molecules
electricity and magnetism
electromagnetic field
general relativity
quantum electrodynamics
Subtopic: light as mass up

Quote: light carries a momentum which is 1/c of its energy; from radiation pressure due to moving charges in a magnetic field [»feynRP_1963]

Subtopic: light as electromagnetic waves up

Quote: light is electromagnetic waves: the speed of electromagnetic waves experimentally agrees with the speed of light in a vacuum, and neither experiment depended on the other view [»maxwJC_1864, OK]
Quote: the propagation of energy takes place through a medium; Maxwell's goal was an accurate, mental representation of this medium [»maxwJC_1891, OK]
Quote: just as the sun sends particles of light, so things give off streams of images in all directions; e.g., reflections from a mirror [»lucr_55]

Subtopic: black-body radiation up

Quote: black-body radiation: real matter always emits light and radiates energy; in a closed box, the radiation and matter reach thermal equilibrium [»feynRP_1963]
Quote: by classical theory, black-body radiation (the color of a furnace) would predominate at high frequency with unbounded total energy
Quote: Planck empirically determined the equation for black-body radiation and found a simple derivation under the assumption that harmonic oscillators have discrete energy levels [»feynRP_1963]
Quote: in the limit, Planck's equation for black-body radiation yields the classical equation, Rayleigh's law

Subtopic: light as decay up

Quote: the sun, moon, and stars emit light and decay; even rocks and shrines decay [»lucr_55]

Subtopic: ether up

Quote: the electromagnetic field travels through an ethereal substance [»maxwJC_1864, OK]
Quote: experiments have shown that ether, i.e., absolute space, does not exist [»poinH_1902, OK]
Quote: the importance of the Michelson-Morley experiment was not seen for 25 years; they thought it supported Stoke's ether theory [»lakaI_1970]
Quote: perhaps information for computer scientists is like ether was for physicists in the last century [»dennPJ3_1995]

Subtopic: speed of light up

Quote: can remove the speed of light from physical equations by defining the unit of time as the time in which light travels 1cm [»einsA_1949]
Quote: in 1656 Roemer measured the speed of light by measuring the discrepancies in the orbits of Jupiter's moons when Jupiter was close to earth and when it was far from earth
Quote: the propagation of light assigns equal tracts to equal time intervals [»einsA_1923]
Quote: if two tracts are measured as equal once and anywhere, they are equal always and everywhere; a foundation for the general theory of relativity
Quote: a bowl of water instantly reflects light from the heavens; light must travel fast [»lucr_55]
Quote: light travels faster than sound so we see the lightening before hearing the thunder, despite both having the same cause [»lucr_55]

Subtopic: least time up

Quote: Fermat's principle of least time: light takes the path which requires the shortest time; it is an approximation for time differences of a period or longer
Quote: use an ellipse to reflect all light from one point to another, i.e., all shortest paths have the same length [»feynRP_1963]
Quote: the principle of least time: small changes to the path only make second-order changes to the time, i.e., there are many nearby paths which take almost exactly the same time [»feynRP_1963]
Quote: the principle of least action for conservative forces: the path taken is the path with the least action; many nearby paths; e.g., the average kinetic energy less the average potential energy [»feynRP_1964]
Quote: Principle of Least Effort: people strive to minimize the average rate of work-expenditure they must use to solve immediate problems and probable future problems [»zipfGK_1949]

Subtopic: refraction, dispersion up

Quote: refraction, the bending of light, comes about because the speed of light is different in different materials; the only way for waves to fit at a boundary is to change the angle; yields Snell's law [»feynRP_1963]
Quote: when light passes through glass it vibrates the electrons in the glass which in turn generate new fields; these fields effectively change the light's speed through the glass [»feynRP_1963]
Quote: dispersion: as the driving frequency rises toward ultraviolet light, the index of refraction rises; so a prism spreads light

Subtopic: spectrum up

Quote: dark spectral lines occur when the light frequency is nearly the natural frequency and the light is absorbed [»feynRP_1963]
Quote: from the sun's spectral lines we know that the chemical elements in the sun and stars are the same as those on earth
Quote: so far as problems involving light are concerned, electrons behave as though they were held by springs, i.e., oscillators with displacement proportional to force [»feynRP_1963]
Quote: the natural frequency of electron oscillators in most ordinary gases and transparent substances corresponds to ultraviolet light [»feynRP_1963]
Quote: adding a light to two, indistinguishable spectral distributions is also indistinguishable [»feynRP_1963]
Quote: if ideal clocks go at the same rate, they always go at the same rate; e.g., sharp spectral lines from atoms of the same chemical element; a foundation of 4-d space-time

Subtopic: color up

Quote: brown light is a dark red and yellow mixture against a lighter background [»feynRP_1963]

Subtopic: radiating atom up

Quote: a screen is opaque when the electric fields generated by the screen exactly cancel the light's electric field; this requires a sufficiently thick screen even for gold [»feynRP_1963]
Quote: a radiating atom loses 1/e'th of its energy in 10^-8 seconds [»feynRP_1963]

Subtopic: scattering up

Quote: distinct light sources do not interfer only if measurements are averaged over more than 10^-8 seconds [»feynRP_1963]
Quote: the scattering of sunlight by air is proportional to the fourth power of the frequency; why the sky is blue [»feynRP_1963]
Quote: the wavelength of light is about 5000 times the diameter of an atom; small groups of atoms scatter light more strongly, but larger droplets scatter red more strongly [»feynRP_1963]

Subtopic: polarized light up

Quote: at right angles to a light beam, scattered light is polarized [»feynRP_1963]
Quote: all electric fields are polarized; unpolarized light is the overlapping of many different polarizations [»feynRP_1963]

Subtopic: reflection up

Quote: a mirror reverses left for right because images are dashed directly backwards and rebound [»lucr_55]
Quote: a mirror apes our every move because images reflect at the angle of attack [»lucr_55]
Quote: light appears to reflect from one point of a mirror because that is where many possible paths take nearly equal time [»feynRP_1985]
Quote: a mirror image reverses front and back, not right and left; e.g., top and bottom not reversed [»bateG_1979]

Subtopic: fire up

Quote: fire comes from lightning or from the rubbing together of trunks and branches [»lucr_55]

Related Topics up

Topic: atoms and molecules (57 items)
Topic: electricity and magnetism (53 items)
Topic: electromagnetic field (63 items)
Topic: general relativity (47 items)
Topic: quantum electrodynamics (34 items)
Topic: time
(49 items)

Updated barberCB 3/06
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