**1. Current (Current):**
Current is the directed movement of electric charges under the influence of an electric field. The strength of the current is measured by its intensity, commonly referred to as current. It represents the amount of electric charge passing through a cross-sectional area of a conductor per unit time. Current is denoted by the symbol *i(t)* and is measured in amperes (A).
**2. Voltage:**
Voltage is a measure of the electric field's ability to do work on a unit positive charge as it moves from one point to another. It reflects the potential difference between two points in a circuit. Voltage is represented by the symbol *u(t)* and is measured in volts (V).
**3. Electromotive Force (EMF):**
Electromotive force (EMF) is a physical quantity that measures the ability of an external non-electric force, such as chemical or mechanical forces, to move a unit positive charge from the negative terminal to the positive terminal of a power source. EMF is denoted by *e(t)* and is also measured in volts (V).
**4. Electric Potential:**
Electric potential at a point in a circuit is defined as the voltage between that point and a chosen reference point. This reference is typically taken as ground. The electric potential is denoted by *V* and is measured in volts (V).
**5. Electrical Energy:**
Electrical energy is the total work done by the electric force over a period of time. It is represented by the symbol *W* and is measured in joules (J).
**6. Thevenin’s Theorem:**
Thevenin’s Theorem states that any linear two-terminal network containing independent sources can be replaced by an equivalent circuit consisting of a single voltage source in series with a resistor. The voltage of the source equals the open-circuit voltage of the original network, and the resistance is the equivalent resistance seen from the terminals when all independent sources are turned off.
**7. Superposition Theorem:**
In a linear circuit, the response (current or voltage) in any branch is equal to the algebraic sum of the responses caused by each independent source acting alone. All other sources are set to zero during each individual calculation.
**8. Kirchhoff’s Current Law (KCL):**
Kirchhoff’s Current Law states that 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 always zero.
**9. Kirchhoff’s Voltage Law (KVL):**
Kirchhoff’s Voltage Law states that the sum of voltage rises around any closed loop in a circuit is equal to the sum of voltage drops. In other words, 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. It states that the voltage across a resistor is directly proportional to the current flowing through it: *u = i × R*.
**11. Reference Direction:**
A reference direction is an assumed direction for current or voltage used during circuit analysis. If the calculated value is positive, the actual direction matches the reference; otherwise, it is opposite.
**12. Rated Value:**
Rated values specify the maximum safe operating limits of electrical equipment, including voltage, current, and power. These values are usually denoted by the subscript *N*.
**13. Power:**
Power is the rate at which electrical energy is consumed or produced in a circuit. It is represented by *P* or *p(t)* and is measured in watts (W).
**14. Active Power:**
Active power, also known as real or average power, is the average value of instantaneous power over a cycle. It is measured in watts (W).
**15. Reactive Power:**
Reactive power measures the energy exchanged between inductive or capacitive components 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 current in an AC circuit. It represents the total power supplied to a load and is 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* and measured in watts (W).
**18. Resistor:**
A resistor is an ideal component that dissipates electrical energy in a circuit. It is denoted by *R* and measured in ohms (Ω).
**19. Inductor:**
An inductor is a component that stores magnetic energy. It is denoted by *L* and measured in henrys (H).
**20. Capacitor:**
A capacitor is a component that stores 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-world components, focusing on a single physical property.
**22. Circuit Model:**
A circuit model is a representation of a real device using ideal components or combinations of them.
**23. Voltage Source:**
A voltage source is an ideal component that provides a constant or time-varying voltage. It is often called an ideal voltage source.
**24. Current Source:**
A current source is an ideal component that supplies a constant or varying current. It is also known 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 complex ratio of voltage to current in a passive two-terminal network. It is measured in ohms (Ω) and is often expressed as a complex number.
**27. Admittance:**
Admittance is the reciprocal of impedance and represents the ease with which current flows through a circuit. It is denoted by *Y* and measured in siemens (S).
**28. Impedance Angle:**
The impedance angle is the phase difference between voltage and current in an AC circuit. It is determined by the circuit’s characteristics.
**29. Phasor:**
A phasor is a complex number used to represent sinusoidal quantities in AC circuits. Its magnitude corresponds to the amplitude or effective value, while its angle represents the initial phase.
**30. Sinusoid:**
A sinusoid is a time-varying quantity, such as voltage or current, that follows a sine or cosine waveform.
**31. Phasor Diagram:**
A phasor diagram is a graphical representation of phasors in 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 one cycle. It is also known as the RMS value.
**33. Inductive Circuit:**
An inductive circuit is one where the voltage leads the current due to the presence of inductors.
**34. Capacitive Circuit:**
A capacitive circuit is one where the voltage lags behind the current due to the presence of capacitors.
**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 signal changes over time, measured in radians per second (rad/s).
**38. Instantaneous Value:**
The instantaneous value is the value of a sinusoidal quantity at a specific moment in time.
**39. Phase:**
Phase is the angle that describes the position of a sinusoidal wave relative to a reference.
**40. Initial Phase:**
The initial phase is the phase of a sinusoidal wave at time *t = 0*.
**41. Phase Difference:**
Phase difference is the angular difference between two sinusoidal signals of the same frequency.
**42. Three-Phase Source:**
A three-phase source consists of three sinusoidal voltage sources with the same amplitude, frequency, and a 120° phase difference between each.
**43. Three-Phase AC Circuit:**
A three-phase AC circuit is powered by a three-phase power supply and is widely used in industrial applications.
**44. Three-Phase Four-Wire System:**
This system includes a neutral wire and is used to supply both line-to-line and line-to-neutral voltages.
**45. Three-Phase Three-Wire System:**
This system does not include a neutral wire and is commonly used in high-voltage transmission.
**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-connected) source, the three windings of a three-phase power supply are connected together at a common point (neutral), and the three phase lines are drawn out. This configuration allows for both line-to-line and line-to-neutral connections.
**Information Organization: Yangzhou Tuopu Electric Technology Co., Ltd.**
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