Georg Simonohm (1March 78716-1July 6, 854) is a German physicist.

Ohm discovered the proportional relationship between current and voltage in resistance, that is, the famous ohm's law; He also proved that the resistance of a conductor is directly proportional to its length and inversely proportional to its cross-sectional area and conductivity. In the case of stable current, the charge moves not only on the surface of the conductor, but also on the whole cross section of the conductor. The international system of units "ohm" of resistance is named after him. The name of ohm is also used in other physical and related technical contents, such as "ohmic contact", "ohmic sterilization" and "ohmmeter".

Chinese name: georg simon ohm.

George simonnom

Alias: georg simon ohm

Nationality: Germany

Place of birth: Hellem.

Date of birth:1March 789 16.

Date of death:1July 6, 854

Occupation: physicist

Graduate School: University of Herun Root.

Faith: Christianity

Major achievements: the discovery of ohm's law

Discovering ohm's law of orientation

Discover ohm's law of hearing

Copley medal

Masterpiece: Mathematical research on electric circuits.

The life of the character

family background

Georg simon ohm was born in Gencheng, Hellem. His father taught himself the knowledge of mathematics and physics, and taught Ohm in his youth, which aroused Ohm's interest in science. However, his achievements are of great significance to our future generations.

Ohm was born in a locksmith's family in Hellem. His father Joan Wolfgan Ohm was a locksmith, and his mother Maria Elizabeth Baker was the daughter of a tailor in Hellem. Ohm's parents have not received formal education, but his father is a respected person, and his self-study level is high enough for him to give his children an excellent education. Some of Ohm's brothers and sisters died in childhood, but only three children survived. These three children are him, his younger brother Martin Ohm (1792- 1872), and his sister Elizabeth Barbara. His mother died when he was ten years old.

Early experience

In early childhood, Georg Simon and Martin were taught a high degree of mathematics, physics, chemistry and philosophy by their father. Georg Simon went to Hellem Gen Senior High School at the age of 1 1 to 15, where he received a little scientific knowledge and felt that what he taught at school was very different from what his father taught. At the age of 15, Georg georg simon ohm was tested by KarlChristianvonLangsdorf, a professor at the University of Herun. He noticed Ohm's outstanding talent in the field of mathematics, and even wrote in his conclusion that another pair of Bernoulli brothers would be born from the locksmith's house.

college life

1805, 16-year-old Ohm entered Herun University to study mathematics, physics and philosophy. Instead of focusing on his studies, he spent a lot of time dancing, skating and playing billiards. Ohm's father was very angry with Ohm for wasting educational opportunities, so he sent Ohm to Switzerland.

1September, 806, Ohm worked as a math teacher in a school in GottstadtbeiNydau.

/kloc-at the age of 0/6, he entered Herun University to study mathematics, physics and philosophy. Dropped out of school due to financial difficulties, and did not finish his doctoral studies until 18 13. Ohm has been a middle school teacher for a long time. Due to the lack of information and instruments, his research work has brought many difficulties. But he has been persistently conducting scientific research and making his own instruments in a lonely and hard environment.

Ohm studied the current in the wire. He was inspired by the law of heat conduction discovered by Fourier, and the heat flow between two points in a heat conducting rod is directly proportional to the temperature difference between the two points. So Ohm thinks that the current phenomenon is similar to this, and guesses that the current between two points in a wire may be proportional to some driving force between them, which is called electromotive force. Ohm spent a lot of energy on this research. At first, he used voltaic pile as power supply, but the effect was not good because of the unstable current. Later, he accepted the advice of others and used thermoelectric battery as power supply, thus ensuring the stability of current. But how to measure the current was still an unsolved problem at that time. At first, ohm used the thermal effect of current to measure the current by expanding with heat and contracting with cold, but it is difficult to get accurate results by this method. Later, he combined the current magnetic effect discovered by Oster with Coulomb torsion balance, and skillfully designed a current torsion balance, in which a twisted wire was used to hang a magnetic needle, so that the electrified wire and the magnetic needle were placed in parallel along the meridian direction. Then a bismuth-copper thermoelectric battery is used, one end of which is immersed in boiling water and the other end is immersed in crushed ice. Two mercury tanks are used as electrodes and connected by copper wires. When the current passes through the wire, the deflection angle of the magnetic needle is proportional to the current in the wire. In the experiment, he measured eight copper wires with the same thickness and different lengths, and obtained the following equation:

X=a/(b+x)

Where x is the intensity of magnetic effect, that is, the magnitude of current; A is a constant related to the exciting force (i.e. temperature difference), i.e. electromotive force; X represents the length of the wire, B is a constant related to the resistance of the rest of the circuit, and b+x actually represents the total resistance of the circuit. This result was published in 1826. 1827, ohm summed up his experimental laws into the following formula in the book Mathematical Research of Electrokinetic Circuits:

S=γE .

Where s stands for current; E stands for electrodynamic force, that is, the potential difference between the two ends of the wire, γ is the conductivity of the wire to the current, and its reciprocal is the resistance.

In the early days of the discovery of Ohm's Law, many physicists could not correctly understand and evaluate this discovery, and were doubted and sharply criticized. The research results were ignored and the economy was extremely difficult, which made Ohm depressed. It was not until 184 1 the Royal Society awarded him the highest honor-the copley Gold Medal, that it attracted the attention of the German scientific community.

Ohm also proved in many of his works that resistance is directly proportional to the length of the conductor and inversely proportional to the cross-sectional area and conductivity of the conductor; In the case of constant current, the charge moves not only on the surface of the conductor, but also on the whole cross section of the conductor.

teaching career

Karl Kristen van Langestoffer left Herun Genuniversity to teach at Heidelberg University on 1809. Ohm proposed to go to Heidelberg with him to start his math study again, but Langestofer suggested that Ohm continue to teach himself math and read the works of Euler, Laplace and Laclau. Ohm accepted Langes's advice and continued to teach himself mathematics.

At the age of 22, Ohm returned to Hellem, where he received his Ph.D. 18 1 for his thesis Light and Color, and then worked as a math lecturer in Hellem for three semesters. Then he taught in Bamberg in 18 13, cologne in18/7 and Berlin in 1826.

Ohm's main research interest was electricity, which had not been widely studied at that time.

1833 became a professor at the Royal Institute of Technology in Nuremberg, 1839 became the president of the school, 1849 became a professor at the University of Munich, and 1852 became a professor of experimental physics.

Adversity life

Ohm loves physics and mathematics. Ohm was taught by his father since childhood and gained a lot of enlightenment in science and technology. During my college years, I had to drop out of school to be a tutor because of difficulties in life. But he kept on studying, and finally finished his studies and got a doctorate. I have taught in many middle schools and insisted on scientific research after heavy work.

Ohm is in the period of rapid development of electricity, and new electrical achievements are constantly emerging. The discovery of other scientists inspired him to further explore an important question: in the circuit using voltaic cells, the current intensity may increase with the increase of the number of cells, but what is the law in this? He is determined to find the answer through experiments.

At that time, there was no instrument to measure the current intensity. Ohm tried to measure the intensity of current by the thermal effect of current, but it didn't work.

182 1 year, Schwaiger and Bergendorf invented the original galvanometer, which encouraged ohm. He used his spare time to learn various processing skills from workers and was determined to make necessary electrical instruments and equipment. In order to accurately measure the current, he skillfully used the magnetic effect of the current to design the current torsion balance. Hang a magnetic needle with a stranded wire so that the electrified wire is placed parallel to the magnetic needle. When there is current in the wire, the magnetic needle deflects at a certain angle, from which the strength of the current in the wire can be judged. He connected his galvanometer to the circuit, creatively marked the dial of the magnetic needle and recorded the experimental data.

In this way, a formula is obtained from the experimental results of 1825, but it is wrong. The results calculated by this formula are inconsistent with Ohm's later experiments. Ohm regretted it, realized the seriousness of the problem, and planned to withdraw the published paper, but it was too late, and the paper had been distributed. He suffered a lot for his hasty way of success, and scientists also expressed disgust at him and thought he was a fake expert.

Ohm is determined to recover the influence and loss, and more importantly, he will continue to find the law through experiments. Ohm needs people's understanding and support at this moment! At that time, a scientist named Poggendorff saw the talent of pursuing truth and being brave in innovation from Ohm, a middle school teacher, and wrote to encourage Ohm to go on. It is suggested that he use a more stable Zeebek thermoelectric battery in the experiment. This battery was invented by Zeebek in 182 1 year. Its principle is that in a circuit composed of two different wires, the temperature of the two joints is different, and the current is stronger. Ohm summoned up his courage and realized it again with thermoelectric batteries. He immersed one connector in boiling water, keeping the temperature at 100℃, and put the other connector in ice, keeping the temperature at 0℃, thus ensuring a power supply that can provide stable voltage. After many experiments, 1827 finally put forward a relationship: X=a/(b+x), where x represents current intensity, a represents electromotive force (after high school physics), b+x represents resistance, b represents internal resistance of power supply, and x represents external circuit resistance. This is ohm's law, which is a milestone contribution in the history of electricity.

However, the scientific community still does not recognize Ohm's scientific discovery, and many people still hold prejudice against him, and even think that the law is too simple to believe. All this made Ohm feel extremely painful and disappointed.

Science is just. 183 1 year, the British scientist Bai Pu Rongsu cited ohm's law many times in his experiments and finally got accurate results. He published it in writing, and people began to pay attention to ohm's law. Since then, physicists have applied ohm's law to the experiments and research of electricity and magnetism.

184 1 year, the Royal Society awarded him the copley Gold Medal, and declared that Ohm's Law was "the most outstanding discovery in the field of precision experiments". He got the honor he deserved.

Ohm died in 1854. Ten years later, the British Association for the Advancement of Science decided to use the name ohm as the name of the resistance unit in memory of him. Whenever people use this word, they always think of this hardworking and talented middle school teacher.

Major achievements

Study electromagnetism from 1820. Ohm's research work is carried out under very difficult conditions. He is not only busy with teaching, but also lacks books, materials and instruments. He can only use his spare time to design and manufacture instruments and carry out related experiments.

1826, ohm discovered an important law in electricity-ohm's law, which was his greatest contribution. This law seems simple to us today, but its discovery process is not as simple as most people think. Ohm worked very hard for this. At that time, people were not clear about the concepts of current intensity, voltage and resistance, especially the concept of resistance, and of course it was impossible to measure it accurately. In addition, Ohm himself rarely had the opportunity to contact contemporary physicists during his research, and his discoveries were all done independently. Ohm creatively used Coulomb method to make a current torsion balance to measure the current intensity, and introduced and defined the precise concepts of electromotive force, current intensity and resistance.

The discovery of ohm's law and its formula has brought great convenience to the calculation of electricity. In memory of him, people set the unit of resistance as ohm (abbreviation "ohm", symbol ω).

Resistor

The abbreviation is "Ou" and the symbol is ω.

ω μ γ α (uppercase ω, lowercase ω), also called big O, is the 24th and last Greek letter.

Ohm —— taking the international ohm as the unit of resistance, it is the resistance of a mercury column with a mass of 14.452 1g, a length of 106.3cm and a constant cross section at the melting temperature of constant current.

Ohm's Law

The first stage of ohm experiment is to explore the relationship between the electromagnetic force attenuation caused by current and the length of wire. The results were published in his first scientific paper 1825 in May. In this experiment, he met with the difficulty of measuring the current intensity. Inspired by the galvanometer invented by German scientist Schveger, he skillfully combined the current magnetic effect discovered by Oster with Coulomb torsion balance method, designed a current torsion balance, and used it to measure the current intensity. Ohm comes from preliminary experiments, and the electromagnetic force of current is related to the length of conductor. This relationship is not directly related to today's ohm's law expression. Ohm did not relate the potential difference (or electromotive force), current intensity and resistance at that time.

Before ohm, although there was no concept of resistance, some people studied the conductivity of metals. 1825 In July, Ohm also studied the relative conductivity of metals with the device used in the previous experiment. He measured various metals by making wires with the same diameter, and determined the relative conductivity of metals such as gold, silver, zinc, brass and iron. Although the experiment was rough and there were many mistakes, the fact that Ohm thought the current was constant in the whole wire showed that the current intensity could be used as an important basic quantity of the circuit, and he decided to study it as a main observation in the next experiment.

In the previous experiment, the battery used by Ohm was a voltaic pile, and the electromotive force of this pile was unstable, which made him very headache. Later, it was suggested to use bismuth-copper thermocouple as power supply, thus ensuring the stability of electromotive force of power supply.

1826, ohm deduced his law with the experimental device shown above. A current torsion balance is installed on the wooden stand, DD' is the glass cover of the torsion balance, CC' is the dial, S is the magnifying glass for observation, M and M' are the mercury cups, abb'a' is the bismuth stand, and one leg of bismuth and copper stand contacts each other, thus forming a thermocouple. A and B are two tin containers used to generate temperature difference. In the experiment, the conductor to be studied is inserted into two cups containing mercury, M and M' respectively, which become the two poles of a thermoelectric battery.

Ohm prepares conductors with the same cross section but different lengths, connects each conductor into the circuit in turn for experiment, observes the deflection angle of the torsion drag pin, and then repeats the operation under different conditions. According to the experimental data, the following relations are summarized:

X=q/(b+l) where x represents the current flowing through the wire, which is proportional to the current intensity, A and B are two parameters of the circuit, and L represents the length of the experimental wire.

Ohm published a paper in April 1826, rewriting Ohm's law as follows: x=ksa/ls is the cross-sectional area of a conductor, k is the conductivity, a is the potential difference between two ends of the conductor, l is the length of the conductor, and x is the current intensity passing through L. If the resistance l'=l/ks is substituted into the above formula, X=a/I' is obtained, which is Ohm's law. 1 ohm is defined as the resistance that just passes through 1 amp when the potential difference is 1 volt. (that is, R=U÷I)

Ohmic contact

Ohmic contact refers to the contact between metal and semiconductor, and the resistance of its contact surface is much smaller than that of the semiconductor itself, which makes most of the voltage drop in the active area rather than the contact surface when the module works.

In order to form a good ohmic contact, there are two prerequisites:

There is a low barrier height between (1) metal and semiconductor.

(2) The semiconductor has a high concentration of impurities (N_ 10×e/cm).

The former can increase the thermal excitation part of the interface current; The latter makes the interface depletion region narrow, and electrons have more opportunities to tunnel directly, while reducing Rc resistance.

If the semiconductor is not silicon, but other semiconductors (such As Ga and As) with high energy Cap, it is difficult to form ohmic contact (there is no suitable metal available), so it is necessary to dope high-concentration impurities on the semiconductor surface to form a metal -n+-norMetal-p+-p structure.

Ohmic sterilization

Ohmic sterilization is a kind of sterilization method to achieve the purpose of sterilization by introducing current to generate heat in food.

Principle: The current used is 50-60 Hz low frequency alternating current. According to Joule's law, at any point in the heated food, the heat generated by current is q = k (gradv. * grad VO)= k(δv)e。

Q—— unit heating power (W/m) at a certain point,

K—— the electrical conductivity (S/m) at a certain point.

S-Siemens unit of conductance, equal to the reciprocal of resistance ohm.

Gradv- is the potential gradient at any point, v/m.

Factors affecting ohmic sterilization

(1) conductivity and temperature

② electric field intensity e and frequency f

(3) the relationship between the position of the fluid in the heater and the heating degree.

(4) Relationship between operation factor and ohmic heating rate

Ohmic sterilization process operation (aseptic process)

1. Pre-sterilization of equipment

It is realized by circulating a sodium sulfate solution with a certain concentration, and the conductivity of the sodium sulfate solution is close to that of the substance to be sterilized. The ohmic heating component, the insulating tube and the cooling tube are heated by current to a certain temperature for sterilization, and the sterilization pressure is controlled by the pressure regulating valve. Other equipment adopts traditional steam sterilization method. The purpose of using sodium sulfate with similar conductivity to the product as the pre-sterilization solution is to avoid the large adjustment of electric energy from pre-sterilization to product sterilization, maintain a smooth and effective transition, and have small temperature fluctuation.

2. The pre-sterilization liquid is discharged after cooling, and the sterilized materials enter. The pressure is adjusted by using sterile air and nitrogen through the back pressure valve.

3. After being heated and sterilized, the materials sequentially enter the heat preservation tube, cooling tube and storage tank for aseptic filling.

4. After the production, cut off the power supply, first clean with clean water, and then clean with 2% sodium hydroxide solution at 80℃ for 30 minutes.

ohmmeter

An ohmmeter is an instrument for measuring resistance, g is an ammeter for internal resistance Rg and full-scale current Ig, and r is a variable resistance, also called zero-setting resistance; The battery is a dry battery, the electromotive force is E, the internal resistance is R, and the red stylus (inserted into the "+"jack) is connected to the negative electrode of the battery; The black stylus (inserted into the "-"jack) is connected to the positive pole of the battery. When the measured resistance Rx.

Anecdotal allusions

Exquisite craft

Ohm's family is very difficult, but he has been well trained since childhood. His father is a skilled locksmith, and he also likes mathematics and philosophy. My father's technical enlightenment made Ohm develop a good habit of hands-on. He is clever and can do anything decent. Physics is an experimental subject. If you only use your brain and don't do it, it's like walking on one leg. You can't walk fast or far. Ohm couldn't have made such achievements without the good skills of carpentry, lathe work and locksmith.

In the experiment of current changing with voltage, it was Ohm who skillfully used the magnetic effect of current to make a current torsion balance and used it to measure the current intensity, thus getting more accurate results.

The light of scientific truth

1827, ohm published "mathematical exposition of galvani circuit", which proved ohm's law in theory. Ohm thought that the research results would be recognized by academic circles and invited him to teach. But he was wrong. The publication of this book attracted a lot of satire and slander, and the university professor looked down on him as a middle school teacher. Bauer, a German, attacked him and said, "People who look at the world with pious eyes should not read this book, because it is simply incredible deception, and its only purpose is to desecrate the dignity of nature." All this made Ohm very sad. In a letter to a friend, he wrote: "The birth of galvanic circuit brought me great pain. I really complain that it is untimely, because people living in the imperial court have little knowledge and can't understand the true feelings of its mother. "

Of course, many people are wronged by Ohm. Schveger, editor-in-chief of the Journal of Chemistry and Physics, who published Ohm's paper, wrote to Ohm: "Please believe that the light of truth behind the dark clouds and dust will eventually be transmitted and dispersed with a smile." Ohm resigned from his post in Cologne and worked as a private school teacher for several years. It was not until seven or eight years later, with the progress of circuit research, people gradually realized the importance of ohm's law, and ohm's reputation was greatly improved.

184 1 year, the Royal Society awarded him the copley Medal.

1842 was hired as a foreign member,

1845 was admitted to the Bavarian Academy of Sciences.

Personality assessment

Georg simon ohm is a brilliant researcher, a man with extraordinary talent and scientific ambition. In memory of him, the unit of resistance "ohm" was named after his surname.