The concept of circuit -- circuit refers to the current channel composed of real components.

The structure of a circuit consists of a power supply, a load and an intermediate link. Power supply is a device that converts other forms of energy into electrical energy and provides electrical energy to the circuit; load is a device that converts electrical energy into other forms of energy and receives electrical energy in the circuit; intermediate links are indispensable links between power supply and load, control and protection components collectively known as intermediate links, such as wires, switches and other components. Various relays and so on.

Functions of Circuits - Circuits in power systems can transmit, distribute and convert electricity; Circuits in electronics can transmit, transform, store and process electrical signals.

Circuit Model-In circuit analysis, in order to facilitate the analysis of actual electrical devices, it is usually necessary to model the actual circuit under certain conditions, that is, to replace the actual device with abstract ideal circuit elements and their combinations approximate, thus constituting a circuit model corresponding to the actual circuit.

Ideal Circuit Element - Ideal Circuit Element is the idealization and approximation of the actual circuit device. Its electrical characteristics are unique and accurate, and can be quantitatively analyzed and calculated. Ideal circuit elements can be divided into active and passive two categories, passive two-terminal components include resistive components (only with the electrical characteristics of energy consumption), inductance components (only with the electrical characteristics of magnetic energy storage). Capacitor element (only has the electrical characteristics of storing electric energy); active two-terminal element includes ideal voltage source (output voltage is constant, output current is determined by it and load together), ideal current source (output current is constant, both ends voltage is determined by it and load together).

In order to facilitate the analysis of the circuit, the direction of voltage and current should be marked on the circuit diagram in advance. The direction of voltage and current on the circuit diagram is called the reference direction and can be assumed arbitrarily in principle. Whether a component is a power source or a load depends on the actual direction of voltage and current on the component: when the actual direction is related, the component is a load; when the actual direction is not related, the component is a power source.

Two, from zero to learn the circuit basis -- current.

Electric current (intensity) -- the quantity of electricity passing through the conductor cross section per unit time.

The size of the current -- (steady DC condition: I=q/t)

The unit of current and conversion -- ampere (A) = Coulomb (C) / second (s) 1A=103mA=106 u A=109nA

Current is a directional physical quantity. It is not enough to point out the magnitude of the current. It is stipulated that the direction in which the positive charge moves is the true direction of the current. When the circuit equations are written, the positive and negative voltage and current are based on the presupposed reference direction on the current diagram. If the calculation results are positive, the true direction of voltage and current is consistent with the reference direction, otherwise the opposite is true.

In order to describe and characterize the scale and size of the energy exchange between charges and components, physical quantities of voltage, potential and electromotive force are introduced.

Three, from zero to learn the circuit basis -- voltage, potential and electromotive force.

Voltage U is the physical quantity of the ability to do work in response to the electric field force, and it is the fundamental reason for generating current. The positive direction of voltage is regulated by the "high" potential to the "low" potential.

The potential V is the voltage relative to the reference point and the potential of the reference point.

EMF E only exists in the power supply, its size reflects the power power to do work, its direction stipulated by the power supply "negative" to the power supply "positive", that is, the direction of potential rise.

Four, from zero to learn the circuit basis -- Electrical and electrical power.

Electric power - electric current can make the motor rotate, electric furnace heat, light, indicating that electric current has the ability to work. The work done by electric current is called electric work. Electric power is measured by energy, which is W = UIt.

The unit of electric work is --U (V) *I (A) *t (s) =W (J); U (KV) *I (*I) (())

Electric power -- the work done in current per unit time is called electric power, and is expressed by "P", P=W/t=UIt/t=UI.

The voltage and current values on the nameplate data of the electrical appliances are called rated values. The so-called rated values refer to the maximum limits under long-term, safe working conditions of the electrical appliances, which are generally calibrated at the time of leaving the factory. The rated power reflects the ability of electrical appliances to convert energy under rated conditions. For example, a "220V 40W" lamp shows that it can convert 40 joules of electricity into light and heat in a second when a 220V voltage is applied at both ends.

Five, from zero to learn the basis of circuit -- Kirchhoff's law.

1, several commonly used circuit nouns:

(1) branch: branch of a series of elements flowing through the same current in a circuit.

(2) node: collection point (connection point) of three or more than three branches.

(3) loop: any closed path in a circuit consisting of branches.

(4) mesh: a single circuit that does not include any branch. Mesh is loop, and loop is not necessarily mesh. Every mesh in a planar circuit is a mesh.

2, the node current law (KCL).

Kirchhoff's Law of Current (KCL) is used to determine the relationship between the currents of the branches connected at the same node. According to the principle of current continuity, charges can not accumulate at any point (including nodes). There is: at any instant, the algebraic sum of the current flowing to a node is equal to zero. The mathematical expression is: (arbitrary waveform current); (current in DC circuit).

Popularization and application: the algebraic sum of the current at any moment through any closed surface is also equal to zero.

3. Circuit voltage law (KVL)
Kirchhoff's voltage law (KVL) is the circuit law used to determine the relationship between the voltages in the circuit. According to the principle of singularity of potential, the value of potential increase must be equal to the value of potential decrease in a circle of circuit. There are: any instant, along the term.

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