Polarization

Polarization or polarisation can refer to:

In the physical sciences

Wikimedia Commons

Wikimedia Commons (or simply Commons) is an online repository of free-use images, sound, and other media files. It is a project of the Wikimedia Foundation.

Files from Wikimedia Commons can be used across all Wikimedia projects in all languages, including Wikipedia, Wikibooks, Wikivoyage, Wikispecies, Wikisource, and Wikinews, or downloaded for offsite use. The repository contains over 30 million media files. In July 2013, the number of edits on Commons reached 100,000,000.

History

The project was proposed by Erik Möller in March 2004 and launched on September 7, 2004. A key motivation behind the setup of a central repository was the desire to reduce duplication of effort across the Wikimedia projects and languages, as the same file had to be uploaded to many different wikis separately before Commons was created.

Several sister projects (e.g. Dutch, Swedish, Danish, Norwegian, Spanish, Basque, Polish, Czech and Slovak Wikipedias) moved all their media content to Commons and stopped allowing local uploading. Some projects, such as the English Wikipedia, have more compliant copyright policy and allow to upload and keep files which are not acceptable at Commons, e.g. fair use images.

Khan Academy

Khan Academy is a non-profit educational organization created in 2006 by educator Salman Khan with the aim of providing a free, world-class education for anyone, anywhere. The organization produces short lectures in the form of YouTube videos. In addition to micro lectures, the organization's website features practice exercises and tools for educators. All resources are available for free to anyone around the world. The main language of the website is English, but the content is also available in other languages.

History

The founder of the organization, Salman Khan, was born in New Orleans, Louisiana, United States to immigrant parents from Bangladesh and India. After earning three degrees from the Massachusetts Institute of Technology (a BS in mathematics, a BS in electrical engineering and computer science, and an MEng in electrical engineering and computer science), he pursued an MBA from Harvard Business School.

In late 2004, Khan began tutoring his cousin Nadia who needed help with math using Yahoo!'s Doodle notepad.When other relatives and friends sought similar help, he decided that it would be more practical to distribute the tutorials on YouTube. The videos' popularity and the testimonials of appreciative students prompted Khan to quit his job in finance as a hedge fund analyst at Connective Capital Management in 2009, and focus on the tutorials (then released under the moniker "Khan Academy") full-time.

Polarization (waves)

Polarization (also polarisation) is a property of waves that can oscillate with more than one orientation. Electromagnetic waves such as light exhibit polarization, as do some other types of wave, such as gravitational waves. Sound waves in a gas or liquid do not exhibit polarization, since the oscillation is always in the direction the wave travels.

In an electromagnetic wave, both the electric field and magnetic field are oscillating but in different directions; by convention the "polarization" of light refers to the polarization of the electric field. Light which can be approximated as a plane wave in free space or in an isotropic medium propagates as a transverse wave—both the electric and magnetic fields are perpendicular to the wave's direction of travel. The oscillation of these fields may be in a single direction (linear polarization), or the field may rotate at the optical frequency (circular or elliptical polarization). In that case the direction of the fields' rotation, and thus the specified polarization, may be either clockwise or counter clockwise; this is referred to as the wave's chirality or handedness.

File

File or filing may refer to:

Services

Information

Computing

Other uses

See also