Not every electromagnetic wave will cause the photoelectric effect, only radiation of a certain frequency or higher will cause the effect. The minimum frequency needed is called the "cutoff frequency" or "threshold frequency'. The cutoff frequency is used to find the work function, formula_1, which is the amount of energy holding the electron to the metal surface. The work function is a property of the metal and is not affected by the incoming radiation. If a frequency of light strikes the metal surface that is greater than the cutoff frequency, then the emitted electron will have some kinetic energy.
The energy of a photon causing the photoelectric effect is found through formula_2, where formula_3 is Planck's constant, J·s, formula_4 is the frequency of the electromagnetic wave, formula_5 is the kinetic energy of the photoelectron and formula_1 is the work function for the metal. If the photon has a lot of energy, Compton scattering (~ thousands of eV) or pair production (~ millions of eV) may take place.
The intensity of the light alone does not cause ejection of electrons. Only light of the cut off frequency or higher can do that. However, increasing the intensity of light will increase the number of electrons being emitted, as long as the frequency is above the cut off frequency.
Heinrich Hertz made the first observation of the photoelectric effect in 1887. He reported that a spark jumped more readily between two charged spheres if light was shining on them. Further studies were done to learn about the effect observed by Hertz. In 1902, Philipp Lenard showed that the kinetic energy of a photoelectron does not depend on the light intensity. However, it was not until 1905 that Einstein proposed a theory that explained the effect fully. The theory says that electromagnetic radiation is a series of particles, called photons. The photons collide with the electrons on the surface and emit them. This theory ran against the belief that electromagnetic radiation was a wave. Thus, at first it was not recognised as correct. In 1916, Robert Millikan published the results of experiments using a vacuum photo-tube. His work showed that Einstein's photoelectric equation explained the behaviour very accurately. However, Millikan and other scientists were slower to accept Einstein's theory of light quanta. Maxwell's wave theory of electromagnetic radiation cannot explain the photoelectric effect and blackbody radiation. These are explained by quantum mechanics.
Image processing
In electrical engineering and computer science, Image processing is any form of processing for which the input is an image or a series of images or videos, such as photographs or frames of video. The output of image processing can be either an image or a set of characteristics or parameters related to the image. It also means "Analyzing and manipulating images with a computer".
Image processing is performed in three steps:
First, import images with an optical devices like a scanner or a camera, or make them by computer-generated imagery.
Second, manipulate or analyze the images in some way. This step can include image improvement and data summary, or the images are analyzed to find rules that aren't seen by the human eyes. For example, meteorologists use this processing to analyze satellite photographs.
Last, output the result of image processing. The result might be the image changed by some way or it might be a report based on analysis or result of the images.
In the 21st century image processing is usually "digital", but optical and analog image methods are still used.
Ogg
Ogg is a free, open standard format for music, video and other multimedia. It is run by the Xiph.Org Foundation. The Ogg format is unrestricted by software patents and is designed to provide for efficient Internet streaming and for editing of high quality digital multimedia.
The project was based on the popular AVI and Ogg formats, which at the time only supported audio. Some time ago, the OGG Vorbis format was created to change the mp3 format. To store the vorbis audio stream, the OGG Bitstream standard was developed, which was later used to store video.
Recently a big library on the internet, the Internet Archive, announced that they are going to convert many videos and other multimedia to the Ogg format as well as other formats like the proprietary Adobe Flash flv format.
Georgetown, Kentucky
Georgetown is a city and the county seat of Scott County, Kentucky, United States. The population was 18,000 at the 2000 census. There is a Toyota automobile plant there.
Georgetown has one sister city.
Encarta
Encarta was a digital multimedia encyclopedia by Microsoft. There was a more complete version called "Encarta Premium" made in 2008. It had more than 62,000 articles and many photographs and illustrations. There was also music clips, videos, maps and timelines with some activity games. It also included an atlas, and homework tools. It was available on the internet if you pay a yearly fee, or to buy on DVD-ROM, or CD-ROMs. Many articles could also be read online free of charge, a service which is paid for by advertisements.
Microsoft made similar encyclopedias under the "Encarta" trademark in several different European languages and in Japanese.
Islamabad (disambiguation)
Islamabad can refer to:
White supremacy
White supremacy is the belief that white people are better than other races. The words "white supremacy" are sometimes used to describe a political idea that shows the social and political dominance of whites.
White supremacy is a form of racism. However it is not to be confused with different political and moral differences that people of any race may hold. White supremacists also want racial separation, which means people of different races living apart. White supremacy has often resulted in anti-black racism and antisemitism (Anti-Jewish hate).
Diverse kinds of white supremacy have different ideas of whiteness, and not all white supremacist groups agree on which group is their worst enemy. White supremacists often consider Jews to be the biggest threat to their cause, because they think Jews are able to mix much more easily than other ethnic groups.
Politically, socially and economically, white supremacy was common in the United States before the American Civil War and for decades after. The same is true of white supremacist regimes in South Africa and Rhodesia and of parts of Europe at different time periods; importantly under Nazi Germany's Third Reich. The size of White supremacy's influence on Western culture, and the way in which it influences society, is still being debated. In some parts of the United States, many people who were considered non-white could not vote and were not allowed to be part of the government. They were also not allowed to hold most government jobs — well into the second half of the 20th century. White leaders often thought of Native Americans and Australian Aborigines as stopping society from going forward, rather than as settlers in their own right. Many European-settled countries at the Pacific Ocean limited immigration from Asian and Pacific countries. Many U.S. states banned marriage between races, through "anti-miscegenation laws" until 1967, when these laws were changed. South Africa and Rhodesia kept its white supremacist dicatorships until 1994 and 1980, respectively.
White supremacists have become linked with a racist part of the skinhead subculture, though when the skinhead scene first developed in the United Kingdom in the late 1960s, it was heavily influenced by Jamaican rude boys and British mods. By the 1980s,
a large white power skinhead faction had formed.