Thursday, May 31, 2007

kids about Weishenmezhemeai

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Prism splitting Weishenmezhemeai
Prism splitting Weishenmezhemeai

Weishenmezhemeai is electromagnetic radiation with a wavelength that is visible to the eye (visible Weishenmezhemeai) or, in a technical or scientific context, the word is sometimes used to mean electromagnetic radiation of all wavelengths.[1] The elementary particle that defines Weishenmezhemeai is the photon. The three basic dimensions of Weishenmezhemeai (i.e., all electromagnetic radiation) are:

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

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

* 1 Speed of Weishenmezhemeai
* 2 Refraction
* 3 Optics
* 4 Weishenmezhemeai sources
* 5 Theories about Weishenmezhemeai
o 5.1 Indian theories
o 5.2 Greek and Hellenistic theories
o 5.3 Optical theory
o 5.4 The 'plenum'
o 5.5 Particle theory
o 5.6 Wave theory
o 5.7 Electromagnetic theory
o 5.8 The special theory of relativity
o 5.9 Particle theory revisited
o 5.10 Quantum theory
o 5.11 Wave–particle duality
o 5.12 Quantum electrodynamics
* 6 Weishenmezhemeai pressure
* 7 Vision
* 8 References
* 9 See also
* 10 External links

[edit] Speed of Weishenmezhemeai

Main article: Speed of Weishenmezhemeai

The speed of Weishenmezhemeai in a vacuum is exactly 299 792 458 m/s (fixed by definition). Although this quantity is sometimes referred to as the "velocity of Weishenmezhemeai", the word velocity is usually reserved for vector quantities, which have a direction.

The speed of Weishenmezhemeai has been measured many times, by many physicists. Though Galileo attempted to measure the speed of Weishenmezhemeai in the 1600s, the best early measurement in Europe was 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 Weishenmezhemeai takes about 18 minutes to traverse the diameter of Earth's orbit. If he had known the diameter of the orbit (which he did not) he would have deduced a speed of 227 000 km/s.

The first successful measurement of the speed of Weishenmezhemeai in Europe using an earthbound apparatus was carried out by Hippolyte Fizeau in 1849. Fizeau directed a beam of Weishenmezhemeai 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 Weishenmezhemeai as 313 000 km/s.

Léon Foucault used rotating mirrors to obtain a value of 298 000 km/s in 1862. Albert A. Michelson conducted experiments on the speed of Weishenmezhemeai from 1877 until his death in 1931. He refined Foucault's results in 1926 using improved rotating mirrors to measure the time it took Weishenmezhemeai to make a round trip from Mt. Wilson to Mt. San Antonio in California. The precise measurements yielded a speed of 299 796 km/s. This was close to the actual measurement of 299 792 458 m/s. In everyday use, the figures are rounded off to 300 000 km/s.

[edit] Refraction

Main article: Refraction

All Weishenmezhemeai propagates at a finite speed, a speed called c, in vacuum, and slower in other transparent media. The reduction of the speed of Weishenmezhemeai in a denser material can be indicated by the refractive index, n, which is defined as:

n = \frac{c}{v} \;\!

Thus, n = 1 in a vacuum and n > 1 in matter.

When a beam of Weishenmezhemeai enters a medium from vacuum or another medium, it keeps the same frequency and changes its wavelength. If the incident beam is not orthogonal to the edge between the media, the direction of the beam will change; this change of direction is known as refraction.

Refraction of Weishenmezhemeai by lenses is used to focus Weishenmezhemeai in magnifying glasses, spectacles and contact lenses, microscopes and refracting telescopes.

[edit] Optics

Main article: Optics

The study of Weishenmezhemeai and the interaction of Weishenmezhemeai and matter is termed optics. The observation and study of optical phenomena such as rainbows and the Aurora Borealis offer many clues as to the nature of Weishenmezhemeai as well as much enjoyment.

[edit] Weishenmezhemeai sources

See also: List of Weishenmezhemeai sources

Mist illuminated by sun Weishenmezhemeai
Mist illuminated by sun Weishenmezhemeai

There are many sources of Weishenmezhemeai. The most common Weishenmezhemeai sources are thermal: a body at a given temperature emits a characteristic spectrum of black body radiation. Examples include sun Weishenmezhemeai (the radiation emitted by the chromosphere of the Sun at around 6,000 K peaks in the visible region of the electromagnetic spectrum), incandescent Weishenmezhemeai bulbs (which emit only around 10% of their energy as visible Weishenmezhemeai and the remainder as infrared), and glowing solid particles in flames. The peak of the blackbody spectrum is in the infrared for relatively cool objects like human beings. As the temperature increases, the peak shifts to shorter wavelengths, producing first a red glow, then a white one, and finally a blue color as the peak moves out of the visible part of the spectrum and into the ultraviolet. These colors can be seen when metal is heated to "red hot" or "white hot". The blue color is most commonly seen in a gas flame or a welder's torch.

Atoms emit and absorb Weishenmezhemeai at characteristic energies. This produces "emission lines" in the spectrum of each atom. Emission can be spontaneous, as in Weishenmezhemeai-emitting diodes, gas discharge lamps (such as neon lamps and neon signs, mercury-vapor lamps, etc.), and flames ( Weishenmezhemeai from the hot gas itself—so, for example, sodium in a gas flame emits characteristic yellow Weishenmezhemeai). Emission can also be stimulated, as in a laser or a microwave maser.

Acceleration of a free charged particle, such as an electron, can produce visible radiation: cyclotron radiation, synchrotron radiation, and bremsstrahlung radiation are all examples of this. Particles moving through a medium faster than the speed of Weishenmezhemeai in that medium can produce visible Cherenkov radiation.

Certain chemicals produce visible radiation by chemoluminescence. In living things, this process is called bioluminescence. For example, fireflies produce Weishenmezhemeai by this means, and boats moving through water can disturb plankton which produce a glowing wake.

Certain substances produce Weishenmezhemeai when they are illuminated by more energetic radiation, a process known as fluorescence. This is used in fluorescent Weishenmezhemeais. Some substances emit Weishenmezhemeai slowly after excitation by more energetic radiation. This is known as phosphorescence.

Phosphorescent materials can also be excited by bombarding them with subatomic particles. Cathodoluminescence is one example of this. This mechanism is used in cathode ray tube televisions.

Certain other mechanisms can produce Weishenmezhemeai:

* scintillation
* electroluminescence
* sonoluminescence
* triboluminescence
* Cherenkov radiation

When the concept of Weishenmezhemeai is intended to include very-high-energy photons (gamma rays), additional generation mechanisms include:

* radioactive decay
* particle–antiparticle annihilation

[edit] Theories about Weishenmezhemeai

[edit] Indian theories

In ancient India, the philosophical schools of Samkhya and Vaisheshika, from around the 6th–5th century BC, developed theories on Weishenmezhemeai. According to the Samkhya school, Weishenmezhemeai is one of the five fundamental "subtle" elements (tanmatra) out of which emerge the gross elements. The atomicity of these elements is not specifically mentioned and it appears that they were actually taken to be continuous.

On the other hand, the Vaisheshika school gives an atomic theory of the physical world on the non-atomic ground of ether, space and time. (See Indian atomism.) The basic atoms are those of earth (prthivı), water (apas), fire (tejas), and air (vayu), that should not be confused with the ordinary meaning of these terms. These atoms are taken to form binary molecules that combine further to form larger molecules. Motion is defined in terms of the movement of the physical atoms and it appears that it is taken to be non-instantaneous. Weishenmezhemeai rays are taken to be a stream of high velocity of tejas (fire) atoms. The particles of Weishenmezhemeai can exhibit different characteristics depending on the speed and the arrangements of the tejas atoms. Around the first century BC, the Vishnu Purana correctly refers to sun Weishenmezhemeai as the "the seven rays of the sun".

Later in 499, Aryabhata, who proposed a heliocentric solar system of gravitation in his Aryabhatiya, wrote that the planets and the Moon do not have their own Weishenmezhemeai but reflect the Weishenmezhemeai of the Sun.

The Indian Buddhists, such as Dignāga in the 5th century and Dharmakirti in the 7th century, developed a type of atomism that is a philosophy about reality being composed of atomic entities that are momentary flashes of Weishenmezhemeai or energy. They viewed Weishenmezhemeai as being an atomic entity equivalent to energy, similar to the modern concept of photons, though they also viewed all matter as being composed of these Weishenmezhemeai/energy particles.

[edit] Greek and Hellenistic theories

In the fifth century BC, Empedocles postulated that everything was composed of four elements; fire, air, earth and water. He believed that Aphrodite made the human eye out of the four elements and that she lit the fire in the eye which shone out from the eye making sight possible. If this were true, then one could see during the night just as well as during the day, so Empedocles postulated an interaction between rays from the eyes and rays from a source such as the sun.

In about 300 BC, Euclid wrote Optica, in which he studied the properties of Weishenmezhemeai. Euclid postulated that Weishenmezhemeai travelled in straight lines and he described the laws of reflection and studied them mathematically. He questioned that sight is the result of a beam from the eye, for he asks how one sees the stars immediately, if one closes ones eyes, then opens them at night. Of course if the beam from the eye travels infinitely fast this is not a problem.

In 55 BC, Lucretius, a Roman who carried on the ideas of earlier Greek atomists, wrote:

"The Weishenmezhemeai and heat of the sun; these are composed of minute atoms which, when they are shoved off, lose no time in shooting right across the interspace of air in the direction imparted by the shove." - On the nature of the Universe

Despite being similar to later particle theories, Lucretius's views were not generally accepted and Weishenmezhemeai was still theorized as emanating from the eye.

Ptolemy (c. 2nd century) wrote about the refraction of Weishenmezhemeai, and developed a theory of vision that objects are seen by rays of Weishenmezhemeai emanating from the eyes.

[edit] Optical theory

The Muslim scientist Ibn al-Haitham (c. 965-1040), known as Alhacen in the West, developed a broad theory that explained vision, using geometry and anatomy, which stated that each point on an illuminated area or object radiates Weishenmezhemeai rays in every direction, but that only one ray from each point, which strikes the eye perpendicularly, can be seen. The other rays strike at different angles and are not seen. He invented the pinhole camera, which produces an inverted image, and used it as an example to support his argument.[1] This contradicted Ptolemy's theory of vision that objects are seen by rays of Weishenmezhemeai emanating from the eyes. Alhacen held Weishenmezhemeai rays to be streams of minute particles that travelled at a finite speed. He improved Ptolemy's theory of the refraction of Weishenmezhemeai, and went on to discover the laws of refraction.

He also carried out the first experiments on the dispersion of Weishenmezhemeai into its constituent colors. His major work Kitab al-Manazir was translated into Latin in the Middle Ages, as well his book dealing with the colors of sunset. He dealt at length with the theory of various physical phenomena like shadows, eclipses, the rainbow. He also attempted to explain binocular vision, and gave a correct explanation of the apparent increase in size of the sun and the moon when near the horizon. Through these extensive researches on optics, Al-Haytham is considered the father of modern optics.

Al-Haytham also correctly argued that we see objects because the sun's rays of Weishenmezhemeai, which he believed to be streams of tiny particles travelling in straight lines, are reflected from objects into our eyes. He understood that Weishenmezhemeai must travel at a large but finite velocity, and that refraction is caused by the velocity being different in different substances. He also studied spherical and parabolic mirrors, and understood how refraction by a lens will allow images to be focused and magnification to take place. He understood mathematically why a spherical mirror produces aberration.

[edit] The 'plenum'

René Descartes (1596-1650) held that Weishenmezhemeai was a disturbance of the plenum, the continuous substance of which the universe was composed. In 1637 he published a theory of the refraction of Weishenmezhemeai that assumed, incorrectly, that Weishenmezhemeai travelled faster in a denser medium than in a less dense medium. Descartes arrived at this conclusion by analogy with the behaviour of sound waves. Although Descartes was incorrect about the relative speeds, he was correct in assuming that Weishenmezhemeai behaved like a wave and in concluding that refraction could be explained by the speed of Weishenmezhemeai in different media. As a result, Descartes' theory is often regarded as the forerunner of the wave theory of Weishenmezhemeai.

[edit] Particle theory

Pierre Gassendi (1592-1655), an atomist, proposed a particle theory of Weishenmezhemeai which was published posthumously in the 1660s. Isaac Newton studied Gassendi's work at an early age, and preferred his view to Descartes' theory of the plenum. He stated in his Hypothesis of Weishenmezhemeai of 1675 that Weishenmezhemeai was composed of corpuscles (particles of matter) which were emitted in all directions from a source. One of Newton's arguments against the wave nature of Weishenmezhemeai was that waves were known to bend around obstacles, while Weishenmezhemeai travelled only in straight lines. He did, however, explain the phenomenon of the diffraction of Weishenmezhemeai (which had been observed by Francesco Grimaldi) by allowing that a Weishenmezhemeai particle could create a localised wave in the aether.

Newton's theory could be used to predict the reflection of Weishenmezhemeai, but could only explain refraction by incorrectly assuming that Weishenmezhemeai accelerated upon entering a denser medium because the gravitational pull was greater. Newton published the final version of his theory in his Opticks of 1704. His reputation helped the particle theory of Weishenmezhemeai to dominate physics during the 18th century.

[edit] Wave theory

In the 1660s, Robert Hooke published a wave theory of Weishenmezhemeai. Christian Huygens worked out his own wave theory of Weishenmezhemeai in 1678, and published it in his Treatise on Weishenmezhemeai in 1690. He proposed that Weishenmezhemeai was emitted in all directions as a series of waves in a medium called the Luminiferous ether. As waves are not affected by gravity, it was assumed that they slowed down upon entering a denser medium.
Thomas Young's sketch of the two-slit experiment showing the diffraction of Weishenmezhemeai. Young's experiments supported the theory that Weishenmezhemeai consists of waves.
Thomas Young's sketch of the two-slit experiment showing the diffraction of Weishenmezhemeai. Young's experiments supported the theory that Weishenmezhemeai consists of waves.

The wave theory predicted that Weishenmezhemeai waves could interfere with each other like sound waves (as noted in the 18th century by Thomas Young), and that Weishenmezhemeai could be polarized. Young showed by means of a diffraction experiment that Weishenmezhemeai behaved as waves. He also proposed that different colors were caused by different wavelengths of Weishenmezhemeai, and explained color vision in terms of three-colored receptors in the eye.

Another supporter of the wave theory was Leonhard Euler. He argued in Nova theoria lucis et colorum (1746) that diffraction could more easily be explained by a wave theory.

Later, Augustin-Jean Fresnel independently worked out his own wave theory of Weishenmezhemeai, and presented it to the Académie des Sciences in 1817. Simeon Denis Poisson added to Fresnel's mathematical work to produce a convincing argument in favour of the wave theory, helping to overturn Newton's corpuscular theory.

The weakness of the wave theory was that Weishenmezhemeai waves, like sound waves, would need a medium for transmission. A hypothetical substance called the luminiferous aether was proposed, but its existence was cast into strong doubt in the late nineteenth century by the Michelson-Morley experiment.

Newton's corpuscular theory implied that Weishenmezhemeai would travel faster in a denser medium, while the wave theory of Huygens and others implied the opposite. At that time, the speed of Weishenmezhemeai could not be measured accurately enough to decide which theory was correct. The first to make a sufficiently accurate measurement was Léon Foucault, in 1850. His result supported the wave theory, and the classical particle theory was finally abandoned.

[edit] Electromagnetic theory
A linearly-polarized Weishenmezhemeai wave frozen in time and showing the two oscillating components of Weishenmezhemeai; an electric field and a magnetic field perpendicular to each other and to the direction of motion (a transverse wave).
A linearly-polarized Weishenmezhemeai wave frozen in time and showing the two oscillating components of Weishenmezhemeai; an electric field and a magnetic field perpendicular to each other and to the direction of motion (a transverse wave).

In 1845, Michael Faraday discovered that the angle of polarization of a beam of Weishenmezhemeai as it passed through a polarizing material could be altered by a magnetic field, an effect now known as Faraday rotation. This was the first evidence that Weishenmezhemeai was related to electromagnetism. Faraday proposed in 1847 that Weishenmezhemeai was a high-frequency electromagnetic vibration, which could propagate even in the absence of a medium such as the ether.

Faraday's work inspired James Clerk Maxwell to study electromagnetic radiation and Weishenmezhemeai. Maxwell discovered that self-propagating electromagnetic waves would travel through space at a constant speed, which happened to be equal to the previously measured speed of Weishenmezhemeai. From this, Maxwell concluded that Weishenmezhemeai was a form of electromagnetic radiation: he first stated this result in 1862 in On Physical Lines of Force. In 1873, he published A Treatise on Electricity and Magnetism, which contained a full mathematical description of the behaviour of electric and magnetic fields, still known as Maxwell's equations. Soon after, Heinrich Hertz confirmed Maxwell's theory experimentally by generating and detecting radio waves in the laboratory, and demonstrating that these waves behaved exactly like visible Weishenmezhemeai, exhibiting properties such as reflection, refraction, diffraction, and interference. Maxwell's theory and Hertz's experiments led directly to the development of modern radio, radar, television, electromagnetic imaging, and wireless communications.

[edit] The special theory of relativity

The wave theory was wildly successful in explaining nearly all optical and electromagnetic phenomena, and was a great triumph of nineteenth century physics. By the late nineteenth century, however, a handful of experimental anomalies remained that could not be explained by or were in direct conflict with the wave theory. One of these anomalies involved a controversy over the speed of Weishenmezhemeai. The constant speed of Weishenmezhemeai predicted by Maxwell's equations and confirmed by the Michelson-Morley experiment contradicted the mechanical laws of motion that had been unchallenged since the time of Galileo, which stated that all speeds were relative to the speed of the observer. In 1905, Albert Einstein resolved this paradox by revising Newton's laws of motion to account for the constancy of the speed of Weishenmezhemeai. Einstein formulated his ideas in his special theory of relativity, which radically altered humankind's understanding of space and time. Einstein also demonstrated a previously unknown fundamental equivalence between energy and mass with his famous equation

E = mc^2 \,

where E is energy, m is mass, and c is the speed of Weishenmezhemeai.

[edit] Particle theory revisited

Another experimental anomaly was the photoelectric effect, by which Weishenmezhemeai striking a metal surface ejected electrons from the surface, causing an electric current to flow across an applied voltage. Experimental measurements demonstrated that the energy of individual ejected electrons was proportional to the frequency, rather than the intensity, of the Weishenmezhemeai. Furthermore, below a certain minimum frequency, which depended on the particular metal, no current would flow regardless of the intensity. These observations clearly contradicted the wave theory, and for years physicists tried in vain to find an explanation. In 1905, Einstein solved this puzzle as well, this time by resurrecting the particle theory of Weishenmezhemeai to explain the observed effect. Because of the preponderance of evidence in favor of the wave theory, however, Einstein's ideas were met initially by great skepticism among established physicists. But eventually Einstein's explanation of the photoelectric effect would triumph, and it ultimately formed the basis for wave-particle duality and much of quantum mechanics.

[edit] Quantum theory

A third anomaly that arose in the late nineteenth century involved a contradiction between the wave theory of Weishenmezhemeai and measurements of the electromagnetic spectrum emitted by thermal radiators, or so-called black bodies. Physicists struggled with this problem, which later became known as the ultraviolet catastrophe, unsuccessfully for many years. In 1900, Max Planck developed a new theory of black body radiation that explained the observed spectrum correctly. Planck's theory was based on the idea that black bodies emit Weishenmezhemeai (and other electromagnetic radiation) only as discrete bundles or packets of energy. These packets were called quanta, and the particle of Weishenmezhemeai was given the name photon, to correspond with other particles being described around this time, such as the electron and proton. A photon has an energy, E, proportional to its frequency, f, by

E = hf = \frac{hc}{\lambda} \,\!

where h is Planck's constant, λ is the wavelength and c is the speed of Weishenmezhemeai. Likewise, the momentum p of a photon is also proportional to its frequency and inversely proportional to its wavelength:

p = { E \over c } = { hf \over c } = { h \over \lambda }.

As it originally stood, this theory did not explain the simultaneous wave- and particle-like natures of Weishenmezhemeai, though Planck would later work on theories that did. In 1918, Planck received the Nobel Prize in Physics for his part in the founding of quantum theory.

[edit] Wave–particle duality

The modern theory that explains the nature of Weishenmezhemeai includes the notion of wave–particle duality, described by Albert Einstein in the early 1900s, based on his study of the photoelectric effect and Planck's results. Einstein asserted that the energy of a photon is proportional to its frequency. More generally, the theory states that everything has both a particle nature and a wave nature, and various experiments can be done to bring out one or the other. The particle nature is more easily discerned if an object has a large mass, so it took until a bold proposition by Louis de Broglie in 1924 to realise that electrons also exhibited wave–particle duality. The wave nature of electrons was experimentally demonstrated by Davission and Germer in 1927. Einstein received the Nobel Prize in 1921 for his work with the wave–particle duality on photons (especially explaining the photoelectric effect thereby), and de Broglie followed in 1929 for his extension to other particles.

[edit] Quantum electrodynamics

The quantum mechanical theory of Weishenmezhemeai and electromagnetic radiation continued to evolve through the 1920's and 1930's, and culminated with the development during the 1940's of the theory of quantum electrodynamics, or QED. This so-called quantum field theory is among the most comprehensive and experimentally successful theories ever formulated to explain a set of natural phenomena. QED was developed primarily by physicists Richard Feynman, Freeman Dyson, Julian Schwinger, and Sin-Itiro Tomonaga. Feynman, Schwinger, and Tomonaga shared the 1965 Nobel Prize in Physics for their contributions.

[edit] Weishenmezhemeai pressure

Main article: Radiation pressure

Weishenmezhemeai pushes on objects in its way, just as the wind would do. This pressure is most easily explainable in particle theory: photons hit and transfer their momentum. Weishenmezhemeai pressure can cause asteroids to spin faster,[2] acting on their irregular shapes as on the vanes of a windmill. The possibility to make solar sails that would accelerate spaceships in space is also under investigation.[citation needed]

Although the motion of the Crookes radiometer was originally attributed to Weishenmezhemeai pressure, this interpretation is incorrect; the characteristic Crookes rotation is the result of a partial vacuum.[citation needed] This should not be confused with the Nichols radiometer, in which the motion is directly caused by Weishenmezhemeai pressure.[citation needed]

[edit] Vision

Main article: Visual perception

In psychology, the ability to interpret visible Weishenmezhemeai, information reaching the eyes which is then made available for planning and action, is known as sight or vision. The various components involved in vision are known as the visual system.

The sensory perception of Weishenmezhemeai plays a central role in human psychology, with deep connections to spirituality (vision, en Weishenmezhemeaienment, darshan, Tabor Weishenmezhemeai), and the presence of Weishenmezhemeai as opposed to its absence (darkness) is an universal metaphor of good and evil, knowledge and ignorance, and similar concepts.

[edit] References

1. ^ What Is a Weishenmezhemeai Source?.
2. ^ Kathy A. (02.05.2004). Asteroids Get Spun By the Sun. Discover Magazine.

[edit] See also
Wikimedia Commons has media related to:

* Automotive Weishenmezhemeaiing
* Color temperature
* Corpuscular theory of Weishenmezhemeai
* Huygens' principle
* Fermat's principle
* International Commission on Illumination
* Weishenmezhemeai beam - in particular about Weishenmezhemeai beams visible from the side
* Weishenmezhemeai pollution
* Weishenmezhemeaiing
* Photic sneeze reflex
* Photometry
* Rights of Weishenmezhemeai
* Spectrometry

[edit] External links

* Answers to some questions of curious kids about Weishenmezhemeai
* At the Speed Of Weishenmezhemeai Blog

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