**1. Current (Current):**
Current is the directed movement of electric charge caused by an electric field. The strength of this flow is measured by current intensity, commonly referred to as current. It is defined as the amount of electric charge passing through a cross-sectional area of a conductor per unit time. Current is represented by the symbol i(t) and is measured in amperes (A).
**2. Voltage:**
Voltage represents the work done by an electric force to move a unit positive charge from one point to another within an electric field. It is a measure of the electric field's ability to do work. Voltage is denoted by u(t) and its unit is volts (V).
**3. Electromotive Force (EMF):**
Electromotive force is a physical quantity that measures the ability of an external force (non-electric force) to move a unit positive charge from the negative terminal to the positive terminal of a power source. It is represented by e(t) and measured in volts (V).
**4. Electric Potential:**
Electric potential at a point in a circuit is the voltage between that point and a chosen reference point. It is denoted by V and measured in volts (V). This concept helps in analyzing circuits by providing a baseline for voltage measurements.
**5. Electrical Energy:**
Electrical energy is the total work done by an electric force over a period of time. It is denoted by W and measured in joules (J).
**6. Thevenin’s Theorem:**
Thevenin’s Theorem states that any linear two-terminal network with independent sources can be replaced by an ideal voltage source in series with a resistor when viewed from the external circuit. The voltage of the equivalent source equals the open-circuit voltage of the original network, while the resistance is the equivalent resistance after all independent sources are turned off.
**7. Superposition Theorem:**
In a linear circuit, the current or voltage in any branch is equal to the algebraic sum of the currents or voltages produced in that branch when each independent source acts alone.
**8. Kirchhoff’s Current Law (KCL):**
At any instant, the sum of currents entering a node is equal to the sum of currents leaving that node. Alternatively, the algebraic sum of all currents at a node is zero.
**9. Kirchhoff’s Voltage Law (KVL):**
At any instant, the sum of voltage rises around a closed loop equals the sum of voltage drops. Alternatively, the algebraic sum of all voltages in a loop is zero.
**10. Ohm’s Law:**
Ohm’s Law describes the relationship between voltage (u), current (i), and resistance (R) in a circuit, expressed as u = i × R.
**11. Reference Direction:**
A reference direction is an assumed direction for current or voltage during circuit analysis. Once set, the actual direction is determined based on the sign of the value. A positive value indicates alignment with the reference direction, while a negative value indicates the opposite.
**12. Rated Value:**
Rated values define the maximum permissible voltage, current, and power for electrical devices. These limits ensure safe and efficient operation. They are often denoted with the subscript N.
**13. Power:**
Power is the rate at which energy is absorbed or delivered by a circuit. It is represented by P or p(t) and measured in watts (W).
**14. Active Power:**
Active power is the average power consumed in a circuit over a cycle. It is also known as real power and is denoted by P, measured in watts (W).
**15. Reactive Power:**
Reactive power measures the energy exchanged between inductors or capacitors and the power supply. It is denoted by Q and measured in volt-amperes reactive (VAR).
**16. Apparent Power:**
Apparent power is the product of the RMS voltage and RMS current in an AC circuit. It represents the total power supplied to a device and is denoted by S, measured in volt-amperes (VA).
**17. Instantaneous Power:**
Instantaneous power is the product of the instantaneous voltage and current at a given moment. It is denoted by p(t) and measured in watts (W).
**18. Resistor:**
A resistor is an ideal component that models the dissipation of electrical energy in a circuit. It is denoted by R and measured in ohms (Ω).
**19. Inductor:**
An inductor is an ideal component used to store magnetic energy in a circuit. It is denoted by L and measured in henrys (H).
**20. Capacitor:**
A capacitor is an ideal component used to store electric energy in an electric field. It is denoted by C and measured in farads (F).
**21. Ideal Circuit Elements:**
Ideal circuit elements are simplified representations of real components, capturing only one specific physical property.
**22. Circuit Model:**
A circuit model is a representation of a real system using ideal components or combinations thereof.
**23. Voltage Source:**
An ideal voltage source provides a constant or varying voltage to a circuit. It is denoted as an ideal voltage source.
**24. Current Source:**
An ideal current source provides a constant or varying current to a circuit. It is denoted as an ideal current source.
**25. Controlled Source:**
A controlled source is a voltage or current source whose value depends on another voltage or current in the circuit.
**26. Impedance:**
Impedance is the ratio of the voltage to the current in a passive two-terminal network. It is a complex number, often called complex impedance, and measured in ohms (Ω).
**27. Admittance:**
Admittance is the reciprocal of impedance and represents the ease with which current flows through a circuit. It is a complex number and measured in siemens (S).
**28. Impedance Angle:**
The impedance angle is the phase difference between the voltage and current in a circuit, determined by the circuit's characteristics.
**29. Phasor:**
A phasor is a complex number used to represent sinusoidal quantities in AC circuits. Its magnitude represents the amplitude, and its angle represents the initial phase.
**30. Sinusoid:**
A sinusoid is a voltage or current that varies according to a sine or cosine function over time.
**31. Phasor Diagram:**
A phasor diagram is a graphical representation of phasors on the complex plane, showing their magnitudes and phase relationships.
**32. Effective Value:**
The effective value of an AC current is the DC current that produces the same heating effect in a resistor over a cycle.
**33. Inductive Circuit:**
An inductive circuit is one where the total voltage leads the total current, indicating a dominant inductive reactance.
**34. Capacitive Circuit:**
A capacitive circuit is one where the total voltage lags behind the total current, indicating a dominant capacitive reactance.
**35. Resistive Circuit:**
A resistive circuit is one where the voltage and current are in phase, indicating no reactive components.
**36. Amplitude:**
Amplitude refers to the maximum value reached by a sinusoidal quantity during its cycle.
**37. Angular Frequency:**
Angular frequency is the rate at which the phase of a sinusoidal wave changes over time.
**38. Instantaneous Value:**
The instantaneous value is the value of a quantity at a specific moment in time.
**39. Phase:**
Phase is the angle that represents the position of a sinusoidal wave in its cycle.
**40. Initial Phase:**
The initial phase is the phase of a sinusoidal wave at time t = 0.
**41. Phase Difference:**
Phase difference is the difference in phase between two sinusoidal quantities of the same frequency.
**42. Three-Phase Source:**
A three-phase source consists of three sinusoidal voltage sources with equal amplitude, same frequency, and 120° phase difference.
**43. Three-Phase AC Circuit:**
A three-phase AC circuit is powered by a three-phase power supply.
**44. Three-Phase Four-Wire System:**
This system includes a neutral wire and is used to provide balanced power distribution.
**45. Three-Phase Three-Wire System:**
This system lacks a neutral wire and is typically used in balanced three-phase applications.
**46. Phase Voltage:**
Phase voltage is the voltage between a phase line and the neutral line in a three-phase system.
**47. Phase Current:**
Phase current is the current flowing through each individual phase in a three-phase system.
**48. Line Voltage:**
Line voltage is the voltage between two phase lines in a three-phase system.
**49. Line Current:**
Line current is the current flowing through each phase line in a three-phase system.
**50. Y-Connected Source:**
In a Y-connected (star) configuration, the three windings of a three-phase source are connected together at a common point (neutral), and three phase lines are drawn out for connection to the load.
**Information Organization: Yangzhou Tuopu Electric Technology Co., Ltd.**
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