Scientifically, the amount of electricity passing through any section of a conductor in unit time is called current intensity, which is called current for short. Usually expressed by the letter I, its unit is ampere (André-Marie Ampère), 1775- 1836, a French physicist and chemist, who has made outstanding achievements in the research of electromagnetic action and contributed to mathematics and physics. Ampere, the international unit of current, is named after its surname. The symbol "a" also guides the directional motion of charges in the body. The free charge in the conductor makes regular directional motion under the action of electric field force, forming current.
The electromotive force of the power supply forms a voltage, and then an electric field force is generated. Under the action of electric field force, at the electrical microampere (μa) of1a =1000ma =1000 000μ a, the directional flow direction of positive charge is electrically specified as the current direction. The microscopic expression of current in a metal conductor is I=nesv, n is the number of free electrons per unit volume, e is the charge amount of electrons, s is the cross-sectional area of the conductor, and v is the charge velocity.
There are many kinds of carriers carrying charges in nature, such as movable electrons in conductors, ions in electrolytes, electrons and ions in plasma and quarks in hadrons. The movement of these carriers forms an electric current.
The basic unit of current in the international system of units is ampere. 1 amp is defined as: two infinite parallel straight lines with a distance of 1 m in vacuum are energized with equal constant current. When the force acting on each meter of conductor is 2× 10-7 N, the current on each conductor is 1 amp.
The definition of 1 amp in primary learning: the amount of charge passing through the conductor section in 1 sec is 1 coulomb, that is, 1 amp = 1 coulomb/sec.
Conversion method:
1kA= 1000A
1A= 1000mA
1mA= 1000μA
1μA= 1000nA
1nA= 1000pA
Some common currents: electronic watch 1.5μA to 2μA, incandescent bulb 200mA, mobile phone 100mA, air conditioner 5A to 10A, high voltage 200A, lightning 20000A to 200000A.
Physically, the direction of current is the direction of positive movement (that is, the positive direction of the speed of positive movement or the opposite direction of the speed of negative movement). The direction of current is opposite to that of electrons.
Charge refers to the free charge, which is the free electron in the metal conductor and the positive ion and negative ion in the aqueous solution of acid, alkali and salt.
Outside the power supply, the current flows from the positive electrode to the negative electrode. Inside the power supply, it flows back from the negative electrode to the positive electrode.