How To Understand Current, Voltage, Resistance, Capacitance And Inductance?

How To Understand Current, Voltage, Resistance, Capacitance And Inductance?

Electric current → The regular movement of electric charges is usually called electric current. Current is divided into AC current and DC current. Ac current refers to the current whose magnitude and direction change periodically with time. For example, three-phase and single-phase AC in the widely used power grid (China's AC frequency is 50Hz, line voltage 380V, phase voltage 220V). Dc current refers to the current whose direction does not change periodically with time, which is generally generated by DC engines, chemical cells, fuel cells, and solar cells. It is mainly used in all kinds of small household appliances, various electronic instruments, electrolytic plating, DC motor electric drive and so on. The symbol of the current is denoted by I, and the unit of the current intensity is "ampere", denoted by A. Units smaller than the ampere are milliamperes (mA) and microamperes (uA), and the conversion units between them are 1A=1000mA, 1mA=1000uA. ② Voltage → refers to the potential difference between two points in the electrostatic field or circuit, the work done by the unit positive charge moving from one point to another under the action of the electric field force, represented by the letter U, its potential is volts; 1V=1000mV, 1mV=1000uV. ③ Resistance → When the current passes through the conductor, due to the existence of resistivity (ρ) in various conductors, on the one hand, it allows the current to pass, on the other hand, it prevents the current from passing, this resistance is called the resistance of the conductor; It is represented by the letter R, and its units are ohms, with units larger than ohms being kilohm (KΩ) and megohm (MΩ); When 1V voltage is applied to both ends of a circuit, the current through the circuit is 1A, then the resistance of this circuit is 1Ω.

After understanding the above three physical units, you can understand Ohm's law, that is, I=U/R current is in A, voltage is in V, resistance is in Ω.

Capacitance → represents two conductors of any shape separated by the medium, under the action of unit voltage, capacity to store electric field energy (charge) capacity of a parameter, expressed by the letter C, the unit is farad (F); Commonly used basic units are milli-method (mF), micromethod (uF), nanomethod (nF), skin method (pF), between them are 1mF=10∧-3F, 1uF=10∧-6F, 1nF= 10-9f, 1pF=10∧-12F.

Capacitance in the AC circuit to the current through the blocking effect, it is referred to as the capacitive reactance, expressed by the symbol Xc, the calculation formula of the capacitive reactance is Xc=1/ωC=1/2πfC. ⑤ Inductance → self-inductance and mutual inductance. When the current in the closed loop changes, the magnetic flux generated by this current through the loop itself also changes, so the induced electromotive force will also be generated in the loop, this phenomenon is called self-induction. The proportional coefficient between the magnetic flux passing through the area surrounded by the loop and the current producing this magnetic flux is called the self-inductance coefficient of the loop, referred to as self-inductance or inductance, and its value is equal to the electromotive force caused by the change of current in a unit time due to self-inductance, expressed by the letter L, the unit is hen (H).

Mutual inductance → If there are two coils close to each other, part of the magnetic flux generated by the current in the first coil is linked to the second coil. When the current in the first coil changes, the magnetic flux of the chain with the second coil also changes, creating an induced electromotive force in the second coil. This phenomenon is called mutual inductance. The magnitude of the inductance between the two coils is expressed by the mutual inductance coefficient. It's also denoted by the letter L. The basic unit of inductance is Henry (H), and the common units are millihen (mH) and microhen (uH), and the conversion relationship is as follows: 1H=10∧3mH=10∧6uH. When the inductor passes the AC current in the AC circuit, the inductance electromotive force will be generated in the coil to hinder the change of the current, commonly known as inductive reactance; It is represented by the letter XL, and the change between it and the voltage and current is expressed by the formula XL=UL/IL. The relationship between inductive reactance of inductor and power supply frequency and inductance of inductor is as follows: XL=ωL=2πfL.