1900-1915

** Marie Curie **

Born in Warsaw on November 7, 1867 ** Marie and Pierre, French physicists and Nobel laureates, who were wife and husband; together, they discovered the chemical elements radium and polonium. The Curies' study of radioactive elements contributed to the understanding of atoms on which modern nuclear physics is based. Pierre Curie was born in Paris on May 15, 1859, and studied science at the Sorbonne. In 1880 he and his brother Jacques (1855-1941) observed that an electric potential is produced when pressure is exerted on a quartz crystal. The brothers named the phenomenon piezoelectricity. In the course of later studies of magnetism, Pierre Curie discovered a certain temperature at which magnetic substances lose their magnetism. In 1895 he was named professor in the School of Physics and Chemistry in Paris. Originally named Marja Sklodowska, Marie Curie was born in Warsaw on Nov. 7, 1867. Her father taught high school physics. In 1891 she went to Paris (where she changed her name to Marie) and enrolled in the Sorbonne. Two years later she passed the examination for her degree in physics, ranking in first place. She met Pierre Curie in 1894, and they married in 1895.
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 * -Died in Passy, France on July 4, 1934 **

Marie Curie was interested in the recent discoveries of radiation. Curie thus began studying uranium radiations, and, using piezoelectric techniques devised by her husband, carefully measured the radiations in pitchblende, an ore containing uranium. When she found that the radiations from the ore were more intense than those from uranium itself, she realized that unknown elements, even more radioactive than uranium, must be present. Marie Curie was the first to use the term radioactive to describe elements that give off radiations as their nuclei break down. **In 1902, she was able to isolate pure radium. Her research was crucial for the understanding and for the use of newly discovered radioactive elements. In 1934, she died from leukemia caused by her long-term exposure to radiation. ** 

 Pierre Curie ended his own work on magnetism to join his wife's research, and in 1898 the Curies announced their discovery of two new elements: polonium (named by Marie in honor of Poland) and radium. During the next four years the Curies, working in a leaky wooden shed, processed a ton of pitchblende, laboriously isolating from it a fraction of a gram of radium. They shared the 1903 Nobel Prize in physics with Becquerel for the discovery of radioactive elements. Marie Curie was the first female recipient of a Nobel Prize. “CURIE, Marie” __Funk and Wagnall’s Encyclopedia__ 1992-1995 ed.


 * Robert Millikan **

[] -Born in Morrison, Illinois on March 22, 1868. “MILLIKAN, Robert Andrews” __Funk and Wagnall’s Encyclopedia__ 1992-1995 ed.
 * -Died in San Marino, California on Dec 19, 1953. **
 * -**He was an American physicist, best known for his work in atomic physics. Millikan was born in Morrison, Ill., and educated at Columbia University and the universities of Berlin and Goettingen. **When he was fourteen, he took a job in a barrelhead factory for almost any pay. The earnings were about one dollar per day. **He joined the faculty of the University of Chicago in 1896, and in 1910 he became professor of physics there. He left the university in 1921 to become director of the Norman Bridge Laboratory of Physics of the California Institute of Technology.
 * In 1908, Millikan carried out several experiments to find the quantity of charge carried by an electron. He started by measuring the path of charged water droplets in an electrical field. The outcome suggested that the charge on the droplets is a multiple of the elementary electric charge. However, the results of the experiment were not precise. He obtained more accurate results with the oil-drop experiment conduced in 1910. In this experiment he replaced water with oil since water evaporated quickly. He sprayed a mist of droplets into a container. Next, he positioned an electrically charged plate above the chamber holding the droplets. Hence, two forces acted on the droplets, gravity and electrical field. The gravity was tending to pull them downward and the electrical field upward. By changing the electrical potential on the plate, he was able to keep the droplets suspended in space. The quantity by which the charge had to be adjusted was equal to the charge of the ion. The experiments yielded values for the charge of an electron, which are very close to those accepted today, 1.602177 x 10-19. An electron carries one unit of negative charge. Its mass is 1/1840 the mass of a hydrogen atom. **


 * Niels Bohr **


 *  [|**http://www.springtimepublishers.com/bp/images/Niels_Bohr.jpg**]

- Date of Birth: Oct. 7 1885 **<span style="font-family: 'Arial','sans-serif'; font-size: 12pt; line-height: 115%; mso-ansi-language: EN-US;">
 * <span style="font-family: 'Arial','sans-serif'; font-size: 12pt; font-weight: normal; line-height: 115%; mso-ansi-language: EN-US; mso-bidi-font-weight: bold;">- Date of Death: Nov. 18 1962 **<span style="font-family: 'Arial','sans-serif'; font-size: 12pt; line-height: 115%; mso-ansi-language: EN-US;">
 * <span style="font-family: 'Arial','sans-serif'; font-size: 12pt; font-weight: normal; line-height: 115%; mso-ansi-language: EN-US; mso-bidi-font-weight: bold;">- Country of origin: Denmark **<span style="font-family: 'Arial','sans-serif'; font-size: 12pt; line-height: 115%; mso-ansi-language: EN-US;">

<span style="font-family: 'Arial','sans-serif'; font-size: 12pt; line-height: 115%; mso-ansi-language: EN-US; mso-bidi-font-weight: bold;">The son of a physiology professor, **<span style="font-family: 'Arial','sans-serif'; font-weight: normal; mso-bidi-font-weight: bold;">throughout his life, he grew up in an analytical environment and he was constantly exposed to new ideas. Since an earl age, Niels showed interest in Math and Physics; and he constantly used his dad's lab to make his experiments. H **e was educated at the University of Copenhagen, where he earned his doctorate in 1911. That same year he went to Cambridge, England, to study nuclear physics under the British physicist Sir Joseph John Thomson, but he soon moved to Manchester to work with Ernest Rutherford. **<span style="font-family: 'Arial','sans-serif'; font-weight: normal; mso-bidi-font-weight: bold;">Bohr helped Rutherford by improving the structure model so that according to quantum mechanics and physics, the model would fit more properly the traits found. ** Bohr’s discovery was about the atomic structure. **<span style="font-family: 'Arial','sans-serif'; font-weight: normal; mso-bidi-font-weight: bold;">He modified Rutherford's model to fit the facts and properties about atoms that had been found. He made the electons be in levels around the nucleus instead of just floating around the nucleus. Bohr also found that the electrons were in specific levels that were ordered according to the amount of energy they had. The ones with greater energy were in the outermost shell, while the ones with least energy were in the innermost shell of the nucleus. **   “BOHR, Niels Henrik David” __Funk and Wagnall’s Encyclopedia__ 1992-1995 ed.