Portal:Physics/2008 Selected articles
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This is an archive of entries that have appeared or will appear on Portal:Physics's Selected Article section in 2007. Articles for previous weeks should not be edited.
Please do not edit this page directly. Instead, use one of the "Edit selected article" links on the right of this page. This will ensure that you edit the correct page for your changes to appear on Portal:Physics in the correct week.
[edit] January
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| Schematic of a neutron |
In physics, the neutron is a baryon that consists of two down quarks and one up quark. Its strong force radiation is the primary force that holds atomic nuclei. It also has a mass of 1.008 664 915 (78) u (1.6749 × 10−27 kg (939.573 MeV/c²), but no electric charge. Neutrons additionally radiate beta decay and have a spin of ½. Neutrons are present in the majority of nuclei, however in a weighted majority they are not. The number of neutrons in a nucleus determines the isotope of the atom. For example, protium, or 1H, is an isotope of Hydrogen with no neutrons, while deuterium, or 2H, contains one. Neutrons were discovered in 1932 by Physicist James Chadwick two years after they were unexplainably detected by Physicist Walther Bothe.
[edit] February
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Erwin Schrödinger (IPA: [ˈɛrviːn ˈʃrøːdɪŋɐ]; August 12, 1887 – January 4, 1961) was an Austrian - Irish physicist who achieved fame for his contributions to quantum mechanics. In 1935, after correspondence with Albert Einstein, he proposed the Schrödinger's cat thought experiment. In 1933, Schrödinger was awarded the Nobel Prize in Physics, along with physicist Paul Dirac for "the discovery of new productive forms of atomic theory" in regard to the Schrödinger equation which he proposed in 1926. One of Schrödinger's lesser-known areas of scientific contribution was his study of color, color perception, and the field of colorimetry
[edit] March
A planetary nebula is an astronomical object consisting of a glowing shell of gas and plasma formed by certain types of stars at the end of their lives. The name originates from a similarity in appearance to giant planets when viewed through a small optical telescope, and is unrelated to planets of the solar system. They are a relatively short-lived phenomenon, lasting a few tens of thousands of years, compared to a typical stellar lifetime of several billion years.
In recent years, Hubble Space Telescope images have revealed many planetary nebulae to have extremely complex and varied morphologies. About a fifth are roughly spherical, but the majority are not spherically symmetric. Their formation depends on the mass of its star; lower mass stars, such as the sun usually form planetary nebulae, while higher mass stars, such as Zeta Ophiuchi will not. The average nebula is approximately 1 light year across.
[edit] April
Microwaves are electromagnetic waves with wavelengths between one meter and one millimeter, or with frequencies between 300 megahertz and 300 gigahertz.
Apparatuses and techniques may be described qualitatively as "microwave" when the wavelengths of signals are roughly the same as the dimensions of the equipment, so that lumped-element circuit theory is inaccurate. As a consequence, devices that utilize microwaves, such as the microwave communications tower pictured, tend to move away from the discrete resistors, capacitors, and inductors used with lower frequency radio waves. Open-wire and coaxial transmission lines give way to waveguides, and lumped-element tuned circuits are replaced by cavity resonators or resonant lines. Similarly to visible light, the phenomena of reflection, polarization, scattering, diffraction, and atmospheric absorption are observed in microwaves.
Microwaves were first theorized in 1864 by James Clerk Maxwell, and were later detected in the 1940s by Sir John Randall and Dr Harry Boot. Since then, microwaves have been used in communication, remote sensing of both earth based and astronomical bodies, food preparation, and non lethal weaponry.
[edit] May
The Speed of Light, or c, is a physical constant equal to exactly 299,792,458 meters per second, or approximately 983,571,056 feet per second, and is the speed of all frequencies of light in a vacuum. Since 1983, the speed of light is used to define the SI unit if one meter. Light can travel at average lower speeds when passing through translucent materials. Denser materials than air, slow the observed speed of light down more than lighter ones do. For instance, light traveling through a diamond travels at approximately 124,000,000 meters per second.
Experimental evidence has shown that the speed of light is independent of the motion of the source. It has also been confirmed experimentally that the two-way speed of light (for example from a source, to a mirror, and back again) is constant. It is not, however, possible to measure the one-way speed of light (for example from a source to a distant detector) without some convention as to how clocks at the source and receiver should be synchronized. Einstein postulated that the speed of light should be taken as constant in all cases, one-way and two-way.
Astronomical distances are sometimes measured in light years (the distance that light would travel in one Earth year, roughly 9.46×1012 kilometres or about 5.88×1012 miles). Because light travels at a large but finite speed, it takes time for light to cover large distances. Thus, the light we observe from distant objects in the universe was emitted from them long ago (pictured is the Crab Nebula as it looked ~6.5 X 103 years ago).
