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Štvrtok, 21. novembra 2024
Piezoelectric Effect (Marie Curie, Pierre Curie)
Dátum pridania: 29.08.2003 Oznámkuj: 12345
Autor referátu: Stromek
 
Jazyk: Angličtina Počet slov: 768
Referát vhodný pre: Stredná odborná škola Počet A4: 2.7
Priemerná známka: 2.97 Rýchle čítanie: 4m 30s
Pomalé čítanie: 6m 45s
 

Marie Curie was the first female recipient of a Nobel Prize.
In 1904 Pierre Curie was appointed professor of physics at the University of Paris, and in 1905 he was named a member of the French Academy. Women not then commonly held such positions, and Marie was not similarly recognized. Pierre's life ended on April 19, 1906, when he was run over by a horse-drawn cart. His wife took over his classes and continued her own research. In 1911 she received an unprecedented second Nobel Prize, this time in chemistry, for her work on radium and radium compounds. She became head of the Paris Institute of Radium in 1914 and helped found the Curie Institute. Marie Curie's final illness was diagnosed as pernicious anaemia, caused by overexposure to radiation. She died in Haute Savoie on July 4, 1934.
The Curies had two daughters, one of whom was also a Nobel Prize winner. Irene Joliot-Curie and her husband, Frédéric, received the 1935 Nobel Prize in chemistry for the synthesis of new radioactive elements.


Piezoelectric Effect, appearance of an electric potential across certain faces of a crystal when it is subjected to mechanical pressure. Conversely, when an electric field is applied on certain faces of the crystal, the crystal undergoes mechanical distortion. Pierre Curie and his brother Jacques discovered the phenomenon in quartz and Rochelle salt in 1880 and named the effect piezoelectricity (from Greek piezein, “to press”).
The piezoelectric effect occurs in several crystalline substances, such as barium titanate and tourmaline. The effect is explained by the displacement of ions in crystals that have a nonsymmetrical unit cell, the simplest polyhedron that makes up the crystal structure. When the crystal is compressed, the ions in each unit cell are displaced, causing the electric polarization of the unit cell. Because of the regularity of crystalline structure, these effects accumulate, causing the appearance of an electric potential difference between certain faces of the crystal. When an external electric field is applied to the crystal, electrostatic forces, resulting in the mechanical deformation of the whole crystal, displace the ions in each unit cell. Because of their capacity to convert mechanical deformation into electric voltages, and electric voltages into mechanical motion, piezoelectric crystals are used in such devices as the transducer, record-playing pickup elements, and the microphone. Piezoelectric crystals are also used as resonators in electronic oscillators and high-frequency amplifiers, because the mechanical resonance frequency of adequately cut crystals is stable and well defined.
 
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