Georg Ohm

Georg Ohm
Georg Simon Ohm (1789-1854)
Born	March 16, 1789 Erlangen, Bavaria, Germany
Died	July 6, 1854 Munich, Germany
Residence	Germany
Nationality	German
Field	Physics
Institutions	University of Munich
Alma mater	University of Erlangen
Academic advisor	Karl Christian von Langsdorf
Known for	Ohm's law Ohm's phase law Ohm's acoustic law
Notable prizes	Copley Medal (1841)

Georg Simon Ohm was a German physicist born on March 16, 1789 in Erlangen, Bavaria. As a high school teacher, Ohm started his research with the recently invented electrochemical cell, invented by Italian Count Alessandro Volta. Later, experimenting with equipment of his own creation, Ohm was able to define the fundamental relationship among electric current, voltage, and resistance. This relationship, known as Ohm's law, represents the true beginning of electrical circuit analysis.

Biography

Early years

Georg Simon Ohm was born on March 16, 1789 to Johann Wolfgang Ohm, a locksmith and Maria Elizabeth Beck, the daughter of a tailor in Erlangen. Although his parents had not been formally educated, Ohm's father was a respected man who had educated himself to a high level and was able to give his sons an excellent education through his own teachings. Some of Ohm's brothers and sisters died in their childhood and only three survived. The survivors, including Georg Simon, were his younger brother Martin who later became a well-known mathematician, and his sister Elizabeth Barbara. His mother died when he was ten.

From early childhood, Georg and Martin were taught by their father who brought them to a high standard in mathematics, physics, chemistry and philosophy. Georg Simon attended Erlangen Gymnasium from age eleven to fifteen where he received little in the area of scientific training, which sharply contrasted with the inspired instruction that both Georg Simon and Martin received from their father. This characteristic made the Ohms bear a resemblance to the Bernoulli family, as noted by the professor at the University of Erlangen, Karl von Langsdorf.

Life in university

In 1805, at age 15, Ohm entered the University of Erlangen. Rather than concentrate on his studies he spent much time dancing, ice skating and playing billiards. Ohm's father, angry that his son was wasting the educational opportunity, sent Ohm to Switzerland where, in September 1806, he took up a post as a mathematics teacher in a school in Gottstadt bei Nydau.

Karl Christian von Langsdorf left the University of Erlangen in early 1809 to take up a post in the University of Heidelberg and Ohm would have liked to have gone with him to Heidelberg to restart his mathematical studies. Langsdorf, however, advised Ohm to continue with his studies of mathematics on his own, advising Ohm to read the works of Euler, Laplace and Lacroix. Rather reluctantly Ohm took his advice but he left his teaching post in Gottstadt bei Nydau in March 1809 to become a private tutor in Neuchâtel. For two years he carried out his duties as a tutor while he followed Langsdorf's advice and continued his private study of mathematics. Then in April 1811 he returned to the University of Erlangen.

Teaching career

His private studies had stood him in good stead for his receiving a doctorate from Erlangen on October 25, 1811 and immediately joined the staff as a mathematics lecturer. After three semesters Ohm gave up his university post because of unpromising prospects while he couldn't make both ends meet with the lecturing post. The Bavarian government offered him a post as a teacher of mathematics and physics at a poor quality school in Bamberg and he took up the post there in January 1813. Feeling unhappy with his job, Georg devoted to writing an elementary book on Geometry as a way to prove his true ability. The school was then closed down in February 1816. The Bavarian government sent him to an overcrowded school in Bamberg to help out with the mathematics teaching.

After that, he sent the manuscript to King Wilhelm III of Prussia upon its completion. The King satisfied with Georg's work and he offered Ohm a position at a Jesuit Gymnasium of Cologne on September 11 1817. Thanks to the school's reputation for science education, Ohm found himself required to teach physics as well as mathematics. Luckily, the physics lab was well-equipped, so Ohm devoted himself to experimenting on physics. Being the son of a locksmith, Georg had some practical experience with mechanical equipment.

He became in the polytechnic school of Nuremberg in 1833, and in 1852 became professor of experimental physics in the university of Munich, where he later died.

The discovery of Ohm's law

In his first paper published in 1825, Ohm examines the decrease in the electromagnetic force produced by a wire as the length of the wire increased. The paper deduced mathematical relationships based purely on the experimental evidence that Ohm had tabulated.

In two important papers in 1826, Ohm gave a mathematical description of conduction in circuits modelled on Fourier's study of heat conduction. These papers continue Ohm's deduction of results from experimental evidence and, particularly in the second, he was able to propose laws which went a long way to explaining results of others working on galvanic electricity. The second paper certainly is the first step in a comprehensive theory which Ohm was able to give in his famous book published in the following year.

What is now known as Ohm's law appeared in the famous book Die galvanische Kette, mathematisch bearbeitet (The Galvanic Circuit Investigated Mathematically) (1827) in which he gave his complete theory of electricity. The book begins with the mathematical background necessary for an understanding of the rest of the work. While his work greatly influenced the theory and applications of current electricity, it was coldly received at that time. It is interesting that Ohm's presents his theory as one of contiguous action, a theory which opposed the concept of action at a distance. Ohm believed that the communication of electricity occurred between "contiguous particles" which is the term Ohm himself uses. The paper is concerned with this idea, and in particular with illustrating the differences in scientific approach between Ohm and that of Fourier and Navier.

Ohm's Law

File:Ohms law voltage source2.svg.png

A voltage source, V, drives an electric current, I , through resistor, R, the three quantities obeying Ohm's law: V = IR.

Ohm's law states that in an electrical circuit, the current passing through a conductor, from one terminal point on the conductor to another, is directly proportional to the potential difference (that is, voltage drop or voltage) across the two terminal points and inversely proportional to the resistance of the conductor between the two points..

In mathematical terms, this is written as:

$I={\frac {V}{R}}$

where I is the current, V is the potential difference, and R is a constant called the resistance. The potential difference is also known as the voltage drop, and is sometimes denoted by E or U instead of V. This law is usually valid over a large range of values of current and voltage, but it breaks down if conditions (such as temperature) are changed excessively.

The SI unit of current is the ampere; that of potential difference is the volt; and that of resistance is the ohm, equal to one volt per ampere. Georg Ohm presented a slightly more complex equation than the above one, to explain his experimental results. The above equation could not exist until the ohm, a unit of resistance, was defined (1861, 1864).

Study and publications

His writings were numerous. The most important was his pamphlet published in Berlin in 1827, with the title Die galvanische Kette mathematisch bearbeitet. This work, the germ of which had appeared during the two preceding years in the journals of Schweigger and Poggendorff, has exerted an important influence on the development of the theory and applications of electric current. Ohm's name has been incorporated in the terminology of electrical science in Ohm's Law (which he first published in Die galvanische Kette...), the proportionality of current and voltage in a resistor, and adopted as the SI unit of resistance, the ohm (symbol Ω).

Although Ohm's work strongly influenced theory, at first it was received with little enthusiasm. However, his work was eventually recognized by the Royal Society with its award of the Copley Medal in 1841 . He became a foreign member of the Royal Society in 1842, and in 1845 he became a full member of the Bavarian Academy.

Works

• Grundlinien zu einer zweckmäßigen Behandlung der Geometrie als höheren Bildungsmittels an vorbereitenden Lehranstalten / entworfen (Guidelines for an appropriate treatment of geometry in higher education at preparatory institutes / notes)

Erlangen : Palm und Enke, 1817. - XXXII, 224 S., II Faltbl. : graph. Darst. (PDF, 11.2 MB)

• Die galvanische Kette : mathematisch bearbeitet (The Galvanic Circuit Investigated Mathematically)

Berlin : Riemann, 1827. - 245 S. : graph. Darst. (PDF, 4.7 MB)

• Elemente der analytischen Geometrie im Raume am schiefwinkligen Coordinatensysteme (Elements of analytic geometry concerning the skew coordinate system)

Nürnberg : Schrag, 1849. - XII, 590 S. - (Ohm, Georg S.: Beiträge zur Molecular-Physik ; 1) (PDF, 81 MB)

• Grundzüge der Physik als Compendium zu seinen Vorlesungen (Fundamentals of physics: Compendium of lectures)

Nürnberg : Schrag, 1854. - X, 563 S. : Ill., graph. Darst. Erschienen: Abth. 1 (1853) - 2 (1854) (PDF, 38 MB)

• Bibliography and PDF files of all articles and books by Georg Simon Ohm

See also

• Ohm (unit)
• Ohm's Law
• Ohm's acoustic law
• Martin Ohm

References

ISBN links support NWE through referral fees

<<This article needs at least 3 reliable references, properly formatted.>> He has demonstrated, both theoretically and experimentally, that the action of a circuit is equal to the sum of the electro-motove forces divided by the sum of the resistances; and that whatever be the nature of the current, whether voltaic or thermo-electric, if this quotient be equal, the effect is the same. The light which these investigations has thrown on the theory of current electricity is very considerable...Had the works of Ohm been earlier known, and their value recognised, the industry of experimentalists would ahve been better rewarded." p 336, Abstracts of the Papers Printed in the Philosphical Transactions of the Royal Society of London from 1837 to 1843 inclusive. Vol IV. London: Richard and John E. Taylor.

External links

• John J. O'Connor and Edmund F. Robertson. Georg Ohm at the MacTutor archive

• This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.

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