what is light?

Answer 1

Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength. The elementary particle that defines light is the photon. The three basic dimensions of light (i.e., all electromagnetic radiation) are:

Intensity (or amplitude), which is related to the human perception of brightness of the light,
Frequency (or wavelength), perceived by humans as the color of the light, and
Polarization (or angle of vibration), which is only weakly perceptible by humans under ordinary circumstances.
Due to the wave-particle duality of matter, light simultaneously exhibits properties of both waves and particles. The precise nature of light is one of the key questions of modern physics.

The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. There are no exact bounds to the visible spectrum; a typical human eye will respond to wavelengths from 400 to 700 nm, although some people may be able to perceive wavelengths from 380 to 780 nm. A light-adapted eye typically has its maximum sensitivity at around 555 nm, in the green region of the optical spectrum (see: luminosity function). The spectrum does not, however, contain all the colors that the human eyes and brain can distinguish. Brown and pink are absent, for example. See Color to understand why.

The optical spectrum includes not only visible light, but also infrared and ultraviolet.

The speed of light in a vacuum is exactly 299,792,458 meters per second (fixed by definition). Although some people speak of the "velocity of light", the word velocity is usually reserved for vector quantities, which have a direction.


The speed of light has been measured many times, by many physicists. The best early measurement in Europe is by Ole Rømer, a Danish physicist, in 1676. By observing the motions of Jupiter and one of its moons, Io, with a telescope, and noting discrepancies in the apparent period of Io's orbit, Rømer calculated that light takes about 18 minutes to traverse the diameter of Earth's orbit. If he had known the diameter of the orbit in kilometers (which he didn't) he would have deduced a speed of 227,000 kilometres per second (approximately 141,050 miles per second).

The first successful measurement of the speed of light in Europe using an earthbound apparatus was carried out by Hippolyte Fizeau in 1849. Fizeau directed a beam of light at a mirror several thousand metres away, and placed a rotating cog wheel in the path of the beam from the source to the mirror and back again. At a certain rate of rotation, the beam could pass through one gap in the wheel on the way out and the next gap on the way back. Knowing the distance to the mirror, the number of teeth on the wheel, and the rate of rotation, Fizeau measured the speed of light as 313,000 kilometres per second.

Léon Foucault used rotating mirrors to obtain a value of 298,000 km/s (about 185,000 miles/s) in 1862. Albert A. Michelson conducted experiments on the speed of light from 1877 until his death in 1931. He refined Foucault's results in 1926 using improved rotating mirrors to measure the time it took light to make a round trip from Mt. Wilson to Mt. San Antonio in California. The precise measurements yielded a speed of 186,285 mi/s (299,796 km/s [1,079,265,600 km/h]). In daily use, the figures are rounded off to 300,000 km/s and 186,000 miles/s.

The different wavelengths are detected by the human eye and then interpreted by the brain as colours, ranging from red at the longest wavelengths of about 700 nm to violet at the shortest wavelengths of about 400 nm. The intervening frequencies are seen as orange, yellow, green, and blue.

Answer 2

Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength. The elementary particle that defines light is the photon. The three basic dimensions of light (i.e., all electromagnetic radiation) are:

* Intensity (or amplitude), which is related to the human perception of brightness of the light,
* Frequency (or wavelength), perceived by humans as the color of the light, and
* Polarization (or angle of vibration), which is only weakly perceptible by humans under ordinary circumstances.

Due to the wave-particle duality of matter, light simultaneously exhibits properties of both waves and particles. The precise nature of light is one of the key questions of modern physics.

Answer 3

Light is a very small cross-section of the entire electromagnetic spectrum, the cross-section that can be freely detected by the naked eye. The electromagnetic spectrum is every frequency and amplitude of radiation that exists including things as benign as color, to ultraviolet rays, infrared rays, microwaves, radio waves, gamma rays, x-rays, etc. Our understanding of the electromagnetic spectrum is still pretty much wholly spoken of in terms of the rays we see emitted from our own sun.

Answer 4

Light is electromagnetic radiation with a wavelength that is visible to the eye

Answer 5

The light is a kind of energy.

Answer 6

It is an electromagnetic emission and propagation.

Answer 7

http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html

Answer 8

somethign that's not heavy