EXCLUSION encyclopedia topics

EXCLUSION - 4 reference results

Healthcare Subrogation
The Phia Group: Legal Expertise in Subrogation and Recovery Law
Sponsored Results PhiaGroup.com

exclusion principle, physical principle enunciated by Wolfgang Pauli in 1925 stating that no two electrons in an atom can occupy the same energy state simultaneously. The energy states, or levels, in an atom are described in the quantum theory by various values of four different quantum numbers; the exclusion principle holds that no two electrons can have the same four quantum numbers in an atom. One of these quantum numbers describes one of the two possible directions for the electron's intrinsic spin. As a result of the exclusion principle, two electrons that are in the same energy level as described by the other three quantum numbers are differentiated from each other because they have opposite spins. This principle applies not only to atoms but to other systems containing particles as well, and it applies not only to electrons but also to a large class of particles collectively known as fermions (see elementary particles).

The Columbia Electronic Encyclopedia Copyright © 2004.
Licensed from Columbia University Press

Healthcare Subrogation
The Phia Group: Legal Expertise in Subrogation and Recovery Law
Sponsored Results PhiaGroup.com

Chinese exclusion

Chinese exclusion, policy of prohibiting immigration of Chinese laborers to the United States; initiated in 1882. From the time of the U.S. acquisition of California (1848) there had been a large influx of Chinese laborers to the Pacific coast. They were encouraged to emigrate because of the need for cheap labor, and were employed largely in the building of transcontinental railroads. By 1867 there were some 50,000 Chinese in California, most of them manual laborers. Their numbers continued to increase after the conclusion in 1868 of the Burlingame Treaty with China, which guaranteed the right of Chinese immigration; it did not, however, grant the right of naturalization. In the following decades a great deal of anti-Chinese sentiment arose in California, partly because the growing American labor force had to compete with cheap Chinese labor and partly because many Americans were opposed to further immigration by what they considered to be an inferior people. In 1877 anti-Chinese riots occurred in San Francisco. Efforts were made to ban Chinese immigration, and in 1879 Congress passed a bill to that effect. It was vetoed, however, by President Hayes on the grounds that it violated the Burlingame Treaty. In 1880 a new treaty with China was concluded; it allowed the United States to regulate, limit, or suspend the entry of Chinese labor, but not to prohibit it. In 1882, however, the Chinese Exclusion Act banned immigration of Chinese laborers for 10 years. Some of the later acts (1888 and 1892) were flat violations of the 1880 treaty. A new treaty was signed in 1894 by which China agreed to exclusion of Chinese laborers for 10 years. When that period expired, Congress continued the exclusion unilaterally until the immigration law of 1924 excluded, in effect, all Asians. In 1943 the acts were repealed when a law was signed setting an annual immigration quota of 105 (since changed) and extending citizenship privileges to Chinese.

See R. D. McKenzie, Oriental Exclusion (1928); S. C. Miller, The Unwelcome Immigrant (1969); B. L. Sung, The Story of the Chinese in America (1971).

The Columbia Electronic Encyclopedia Copyright © 2004.
Licensed from Columbia University Press

Pauli exclusion principle

Assertion proposed by Wolfgang Pauli that no two electrons in an atom can be in the same state or configuration at the same time. It accounts for the observed patterns of light emission from atoms. The principle has since been generalized to include the whole class of particles called fermions. The spin of such particles is always an odd whole-number multiple of 12. For example, electrons have spin 12, and can occupy two distinct states with opposite spin directions. The Pauli exclusion principle indicates, therefore, that only two electrons are allowed in each atomic energy state, leading to the successive buildup of orbitals around the nucleus. This prevents matter from collapsing to an extremely dense state.

Learn more about Pauli exclusion principle with a free trial on Britannica.com.

Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.