What is Ohm's Law?

Ohm's law means that in the same circuit, the current passing through a certain section of conductor is proportional to the voltage across this section of conductor and inversely proportional to the resistance of this section of conductor. The law was proposed by the German physicist George Simon Ohm in the paper "Measurement of the Law of Metal Conduction" published in April 1826.

Common short description: In the same circuit, the current through a conductor is proportional to the voltage across this conductor, and inversely proportional to the resistance of this conductor. This is Ohm's law.

Standard:

(Transformation formula:

;

)

Note: The unit of physical quantity in the formula: I: (current) The unit is

The first phase of Ohm s experiment was to explore the generation of current

In May 1825, Ohm published in his first scientific paper the relationship between the attenuation of the electromagnetic force generated by the current and the length of the wire. It was a paper on Galvani circuits, but the formula was wrong.

In April 1826, Ohm corrected this error and came to the famous Ohm's law.

In 1827, he published his most famous book, The Mathematical Dissertation of Galvani Circuits. The formula is listed in the article, which clearly states that the magnitude of the current in Galvani circuits is proportional to the total voltage and inversely proportional to the total resistance of the circuit. Where S is the current intensity (I) in the conductor, A is the voltage across the conductor (U), and L is the resistance (R) of the conductor. It can be seen that this is the formula of Ohm's law for some circuits today.

In 1876,

Ohm's law applies only

There is a section of metal conductor with a cross-sectional area of S and a length of L. When a voltage U is applied to both ends of the conductor, the field strength in the conductor is E = U / L. At this time, a free electron in the electric field force F = eE To do directional movement. Let the mass of the electron be m, then the acceleration of the directional movement is a = F / m = eE / m = U (e / mL).
Free electrons in motion must frequently collide with positive metal ions, causing their directional movement to be damaged, which limits the increase of the movement rate. After the collision, free electrons have the same chance of ejecting in all directions, and have lost the characteristics of directional movement. They must start the directional acceleration motion with a muzzle velocity of 0 from the beginning.
The interval between two consecutive collisions of free electrons is long or short. If the average time is t, then the directional moving rate of free electrons before the next collision is vt (with t as the subscript) = at, then the average rate v in time t = at / 2. Combined with a = U (e / mL), the average moving rate of free electrons is v = U (et / 2mL).
Substituting the microscopic expression of current I = neSv, I = U (ne ² St / 2mL)
For a certain metal material, at a certain temperature, t is a certain value (10 ^-14 ~ 10s), that is, for a section of metal conductor, ne ² St / 2mL is a constant.
Therefore, the strength of the current I in the conductor is proportional to the voltage U at both ends. The ratio of the voltage across the conductor to the intensity of the current in the conductor (2mL / ne ² St) is the resistance of this conductor. It can be seen that the resistance of the conductor is proportional to the length, inversely proportional to the cross-sectional area, and proportional to 1 / ne ^ 2t. 1 / ne ² t is determined by the characteristics of the conductor. Therefore, at a certain temperature, the resistance of the conductor is R = L / S. is the resistivity of the conductor. For a certain temperature and the same conductor, the resistivity is constant.

Ohm's law is a very accurate law for electronically conductive conductors (such as metals) under normal or low temperature conditions. When the temperature reaches a certain temperature, the metal conductor may enter from the normal state

Electrical and electronic engineering

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The discovery of Ohm's law and its formula has brought great convenience to the calculation of electricity. This is a landmark contribution in the history of electricity. Ohm passed away in 1854. Ten years later, in order to commemorate him, the British Council for the Advancement of Science set the unit of resistance as ohms, referred to as "Europe", and the symbol is . It is a unit of measurement of resistance value. unit. ^[3]