Portal:Physics/Selected article/July 2010

Sunlight takes about 8 minutes, 19 seconds to reach Earth.

White light dispersed by a prism into the colors of the optical spectrum.

The theme of the month is "Light". The following articles discuss different aspects of light that have been researched and discovered over time.

• Light can have two general meanings. Light is what occurs as we experience the visible spectrum of electromagnetic radiation, and in physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not.

• Speed of light is a quantity that does not vary, and expresses how fast light travels in a vacuum. Moreover, according to the theory of relativity, this value appears in the famous equation of E = mc². This invariance of the speed of light was postulated by Albert Einstein in 1905, motivated by Maxwell's theory of electromagnetism and the lack of evidence for the luminiferous ether. Study of this phenomenon explores consequences such as moving objects will shorten, and time dilation (moving clocks run slower).

• Photon has several interrelated descriptions. One of these is that the photon is the basic unit of light, and all electromagnetic radiation. It is also a carrier of the "force" that causes the interaction between electrically charged particles in electromagnetism and electrodynamics. It also has a dual nature. This means it can travel and transfer energy from one point to another; propagating (traveling) through space and time as a wave. Or it can be viewed as a fundamental particle that is not known to be made up of smaller particles. Hence, it is considered to be one of the basic building blocks of the universe.

• Optics is the branch of physics which studies the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties. In addition, the sub-fields of optics are briefly discussed and linked to their respective main articles.

Physicist biographies

Sir Arthur Schuster

John William Strutt

Sir Arthur Schuster (FRS) (12 September 1851 – 17 October 1934) was a versatile German-born British physicist known for his work in spectroscopy, electrochemistry, optics, X-radiography and the application of harmonic analysis to physics. He contributed enormously to making the University of Manchester a centre for the study of physics. (Click on the name to read the entire article)

John Strutt, 3rd Baron Rayleigh (OM) (12 November 1842 – 30 June 1919) was an English physicist who, with William Ramsay, discovered the element argon, an achievement for which he earned the Nobel Prize for Physics in 1904. He also discovered the phenomenon now called Rayleigh scattering, explaining why the sky is blue, and predicted the existence of the surface waves now known as Rayleigh waves. In 1910 Lord Rayleigh discovered that an electrical discharge in nitrogen gas produced "active nitrogen", an allotrope considered to be monatomic. The "whirling cloud of brilliant yellow light" produced by his apparatus reacted with quicksilver to produce explosive mercury nitride. (Click on the name to read the entire article)