Explanations of electrical terms

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1. Resistivity—also known as the resistance coefficient or specific resistance. It is a physical quantity used to measure the conductivity of a material, denoted by the letter ρ, with the unit of ohms*millimeters squared per meter. Numerically, it is equal to the resistance value at 20°C of a wire made of that material with a length of 1 meter and a cross-sectional area of 1 square millimeter; the higher the resistivity, the lower the electrical conductivity. It is a physical quantity that describes how the resistivity of a material changes with temperature; its value is equal to the ratio of the increase in resistivity per 1°C rise in temperature to the original resistivity. It is usually denoted by the letter α, and its unit is 1/C. 2. Temperature coefficient of resistance——a physical quantity that indicates how the resistivity of a material changes with temperature; its value is equal to the ratio of the increase in resistivity per 1°C rise in temperature to the original resistivity. It is usually denoted by the letter α, with the unit of 1/C. 3. Conductivity----The ability of a material to conduct electric current is called conductivity. In a direct current circuit, the value of conductance is the reciprocal of the resistance value; it is denoted by the letter g, with the unit being ohms. 4. Conductivity——also known as the conductance coefficient, is another physical quantity used to measure the degree to which a material conducts electricity. The size is numerically the reciprocal of the resistivity, denoted by the letter γ, with units of meters/ohm*millimeter squared. 5. Electromotive force——The potential difference in a circuit that results from the conversion of other forms of energy into electrical energy is called electromotive force, or simply voltage. It is denoted by the letter E, with the unit being volts. 6. Self-inductance——When the current in a closed circuit changes, the magnetic flux passing through the circuit itself, generated by this current, also changes. As a result, an induced electromotive force is generated within the circuit. This phenomenon is known as self-inductance, and such an induced electromotive force is called a self-induced electromotive force. 7. Mutual inductance——If two coils are placed close to each other, part of the magnetic flux generated by the current in the first coil links with the second coil. When the current in the first coil changes, the magnetic flux linked with the second coil also changes, thereby generating an induced electromotive force in the second coil. This phenomenon is called mutual inductance. 8. Inductance——a general term for self-inductance and mutual inductance. 9. Inductive reactance——When alternating current flows through a circuit that contains an inductor, the inductor resists the flow of this alternating current; this resistance is known as inductive reactance, denoted by Lx. The formula for Lx is Lx=2πfL. 10. Capacitive reactance——When alternating current flows through a circuit that contains a capacitor, the capacitor resists the flow of this alternating current; this resistance is known as capacitive reactance, denoted by Cx. The formula for Cx is Cx=1/2πfc. 11. Pulsating current——A current whose magnitude changes over time while its direction remains constant is called a pulsating current. 12. Amplitude----The maximum value that an alternating current reaches within one cycle is called the amplitude. 13. Average value----The average value of alternating current refers to the ratio of the total charge that flows through a circuit over a certain period of time to that period of time. The average value of a sine wave usually refers to the average value over its positive half-cycle, and its relationship with the amplitude is: average value = 0.637 * amplitude value. 14. Effective value——In two identical resistive devices, when direct current and alternating current are passed through them respectively, if they generate the same amount of heat over the same time period, then the magnitude of the direct current is considered to be the effective value of the alternating current. The effective value of a sinusoidal current is equal to 0.707 times its maximum value. 15. Active power——also known as average power. The instantaneous power of alternating current is not a constant value; the average value of power over one cycle is called real power. It represents the power consumed by the resistive elements in a circuit, and it is denoted by the letter P, with the unit being watt. 16. Apparent power——In a circuit with resistance and reactance, the product of voltage and current is called apparent power, denoted by the letter Ps, and its unit is watt. 17. Reactive power——In circuits with inductors and capacitors, these energy-storing elements convert the energy from the power source into energy of magnetic fields (or electric fields) during half a cycle, and then return the stored energy of magnetic fields (or electric fields) to the power source during the other half cycle. They only exchange energy with the power source; they do not actually consume energy. We call the amplitude value of the rate at which energy is exchanged with the power source reactive power. Denoted by the letter Q, with the unit being zeptos. 18. Power factor——In a DC circuit, the product of voltage and current is the active power. But in AC circuits, the product of voltage and current is the apparent power, while the part of the power that can do work (i.e., the real power) is less than the apparent power. The ratio of real power to apparent power is called the power factor, denoted by COSφ. 19. Phase voltage——The voltage between a three-phase transmission line (live wire) and the neutral wire is called phase voltage. 20. Line voltage——The voltage between the various wires (phase wires) in a three-phase transmission line is called line voltage, and its value is 1.73 times that of the phase voltage. 21. Phasor——In electrical engineering, a vector used to represent the magnitude and phase of a sinusoidal quantity is called a phasor, or vector. 22. Flux——The product of the magnetic flux density and the area perpendicular to the direction of the magnetic field is called flux, denoted by the letter φ, and its unit is the Maxwell. 23. Magnetic flux density——The magnitude of magnetic flux passing through a unit area is called magnetic flux density, denoted by the letter B. The value of magnetic flux density is equal to that of magnetic field intensity. 24. Magnetic resistance – Similar in meaning to resistance, magnetic resistance represents the opposition exerted by a magnetic circuit on magnetic flux; it is denoted by the symbol Rm, and its unit is 1/henry. 25. Permeability——also known as the magnetic permeability coefficient, is a factor that measures a material’s ability to conduct magnetism; it is denoted by the letter μ, with the unit of henry per meter. 26. Hysteresis——During the repeated magnetization of a ferromagnet, the change in its magnetic flux density always lags behind the change in its magnetic field strength; this phenomenon is known as hysteresis. 27. Hysteresis loop——In a magnetic field, the relationship between the magnetic induction intensity of a ferromagnet and the magnetic field strength can be represented by a curve. When the magnetizing field varies periodically, the relationship between the magnetic induction intensity within the ferromagnet and the magnetic field strength forms a closed curve, which is known as the hysteresis loop, as shown in Figure 1. 28. Basic magnetization curve——The shape of the hysteresis loop of a ferromagnet is related to the maximum value of magnetic flux density (or magnetic field strength). When drawing hysteresis loops, by using different values for the maximum magnetic flux density (or magnetic field strength), a series of such loops are obtained; the curve that connects the vertices of these loops is called the basic magnetization curve. 29. Hysteresis loss——In a ferromagnet placed in an alternating magnetic field, certain power losses occur due to the hysteresis phenomenon, which causes the ferromagnet to heat up; this type of loss is known as hysteresis loss. 30. Breakdown——The phenomenon in which an insulating material undergoes intense discharge or becomes conductive under the influence of an electric field is called breakdown. 31. Dielectric constant—also known as dielectric constant, dielectric coefficient, or permittivity—is a coefficient that indicates the insulating capacity of a material; it is denoted by the letter ε, with the unit of farads per meter. 32. Electromagnetic induction—When the magnetic flux passing through a conductor linked by a loop changes, an electromotive force is generated within the conductor; this phenomenon is known as electromagnetic induction. 33. Skin effect—also known as the skin effect phenomenon—occurs when high-frequency current flows through a conductor; the current tends to concentrate on the surface of the conductor, and this is what is referred to as the skin effect