Johannes Georg Bednorz

(1950)

Johannes Georg Bednorz

Johannes Georg Bednorz worked with Alexander Muller to make breakthroughs in the field of superconductivity. Their work advanced the development of superconductors in computers. It also led to more efficient equipment to generate and distribute electricity.

Bednorz, born in 1950 in Germany, was the co-recipient, along with Muller, of the Nobel Prize in 1987. Bednorz currently manages the high-temperature and superconductivity research group at IBM's Zurich laboratory.

Ampere's most notable achievements were his independent determination (1814) of Avogadro's law and his work from 1820 to 1827 based on Oersted's discovery, announced in 1820, that a magnetic needle moves in the vicinity of an electric current. Ampere succeeded in explaining the latter phenomenon by assuming that an electric current is capable of exciting a magnetic field.  He further demonstrated that the direction of the magnetic field is determined by the direction of the current.  He developed a quantitative relationship for the strength of a magnetic field in relation to an electric current (Ampere's theorem) and propounded a theory as to how iron becomes magnetized.  Ampere also devised a rule governing the mutual interaction of current-carrying wires (Ampere's law) and produced a definition of the unit of measurement of current flow, now known as the ampere.

The ampere is the unit for measuring electric current. As more accurate procedures have been devised, the definition of the quantity has been changed. The most modern definition is based on the ability of a specified current to deposit a precise amount of a substance on an electrode during electrolysis. Formerly, the definition involved the force that was produced between parallel wires carrying a current; still earlier, the ampere was defined as a flow of one coulomb per second, where the coulomb (a quantity of electrical charge) was taken as the basic unit.


Ampere inventions

Ampère and corrosion monitoring
The city of Lyon refused to carry out instructions from Paris and the city was besieged for two months. On the fall of the city Ampère's father was arrested for issuing an arrest warrant for the Jacobin Chevalier who had then been put to death. While Ampère moved to Bourg where he taught physics and chemistry but his research was in mathematics. This research resulted in him composing a treatise on probability, The Mathematical Theory of Games, which he submitted to the Paris Academy in 1803. Laplace noticed an error, explaining the error to Ampère in a letter, which Ampère was able to correct and the treatise was reprinted.

Appointed professor of mathematics at the Ecole Polytechnique in 1809 he held posts there until 1828. Ampère was appointed to a chair at Université de France in 1826 which he held until his death. In Paris Ampère worked on a wide variety of topics. Although a mathematics professor, his interests included, in addition to mathematics, metaphysics, physics and chemistry. In mathematics he worked on partial differential equations, producing a classification which he presented to the Institut National des Sciences in 1814 to which he was admitted November of the same year.

Ampère was also making significant contributions to chemistry. In 1811 he suggested that an anhydrous acid prepared two years earlier was a compound of hydrogen with an unknown element, analogous to chlorine, for which he suggested the name fluorine. Ampère also worked on the theory of light, publishing on refraction of light in 1815. By 1816 he was a strong advocate of a wave theory of light, agreeing with Fresnel and opposed to Biot and Laplace who advocated a corpuscular theory. In the early 1820's, Ampère attempted to give a combined theory of electricity and magnetism after hearing about experimental results by the Danish physicist Hans Christian Orsted. Ampère formulated a circuit force law and treated magnetism by postulating small closed circuits inside the magnetized substance.

Another scientist working on magnetism at this time was Poisson who insisted on treating magnetism without any reference to electricity. Poisson had already written two important memoirs on electricity and he published two on magnetism in 1826.

Ampère's most important publication on electricity and magnetism was also published in 1826. Ampère's theory became fundamental for 19th century developments in electricity and magnetism. Faraday discovered electromagnetic induction in 1831 and, after initially believing that he had himself discovered the effect in 1822, Ampère agreed that full credit for the discovery should go to Faraday. Weber also developed Ampère's ideas as did Thomson and Maxwell.

In 1826 Ampère began to teach at the Collège de France. He was there in a position to teach courses of his own instead of topics set for him as was the case at Ecole Polytechnique. Ampère thus taught electrodynamics and this course was taken by Liouville in 1826-27. Liouville made an important contribution to Ampère's electrodynamics course by editing a set of notes taken from Ampère's lectures.


Ampere's Law
The magnetic field in space around an electric current is proportional to the electric current which serves as its source, just as the electric field in space is proportional to the charge which serves as its source. Ampere's Law states that for any closed loop path, the sum of the length elements times the magnetic field in the direction of the length element is equal to the permeability times the electric current enclosed in the loop.


Ampere's Law Applications

1) Magnetic field inside a long Solenoid

A long straight coil of wire can be used to generate a nearly uniform magnetic field similar to that of a bar magnet. Such coils, called solenoids, have an enormous number of practical applications. The field can be greatly strengthened by the addition of an iron core. Such cores are typical in electromagnets.


2) Magnetic Field inside a toroidal coil (Toroid)

Finding the magnetic field inside a toroid is a good example of the power of Ampere's law. The current enclosed by the dashed line is just the number of loops times the current in each loop.

The toroid is a useful device used in everything from tape heads to tokamaks.

3) Magnetic field from a long straight wire



The magnetic field lines around along wirewhich carries an electric current form concentric circles around the wire. The direction of the magnetic field is perpendicular to the wire and is in the direction the fingers of your right hand would curl if you wrapped them around the wire with your thumb in the direction of the current.

with the support of http://hyperphysics.phy-astr.gsu.edu

 
   
 
 
 
     

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