“impedance”的概念、定义、翻译、参考文献-科学参考

impedance

Physics

Symbol Z. The quantity that measures the opposition of a circuit to the passage of a current and therefore determines the amplitude of the current. In a d.c. circuit this is the resistance (R) alone. In an a.c. circuit, however, the reactance (X) also has to be taken into account, according to the equation: Z²=R²+X², where Z is the impedance. The complex impedance is given by Z=R+iX, where i=√−1. The real part of the complex impedance, the resistance, represents the loss of power according to Joule’s law. The ratio of the imaginary part, the reactance, to the real part is an indication of the difference in phase between the voltage and the current.

Electronics and Electrical Engineering

1. (symbol: Z; unit: ohm) A measure of the response of an electric circuit to an alternating current. The current is opposed by the capacitance and inductance of the circuit in addition to the resistance. The total opposition to current flow is the impedance, which is given by the ratio of the voltage to the current in the circuit.
The alternating current is given by
$I = I_{o} cosω t$
where I_o is the peak current and ω is the angular frequency. When reactance, due to the capacitance and inductance, is present in a circuit, the voltage will be out of phase with the current and is given by
$V = V_{o} cos (ω t + ϕ)$
where ϕ is the phase angle. In a circuit containing resistance, R, capacitance, C, and inductance, L, the voltage is given by
$V_{o} cos (ω t + θ) = I R + L (\frac{d I}{d t}) + \frac{1}{C} \int^{} I d t$
Solving this equation shows that the current is equal to
$I = \frac{V_{o} cos (ω t + ϕ)}{\sqrt{[R^{2} + (ω^{2} L^{2} - \frac{1}{ω^{2} C^{2}})]}}$
Since the impedance is the ratio of current to voltage then
$Z = \sqrt{[R^{2} + (ω^{2} L^{2} - \frac{1}{ω^{2} C^{2}})]} = \sqrt{[R^{2} + X^{2}]}$
where X is the reactance. Z is thus a complex quantity whose magnitude or modulus |Z| is equal to the vector sum of R and X. The complex impedance can thus be given by
$Z = R + j X$
where j is equal to √–1. The real part, the resistance, represents a loss of power due to dissipation. The imaginary part, the reactance, indicates the phase difference between the voltage and current (see j). It is either positive or negative depending on whether the current lags or leads the voltage, respectively. In a circuit containing only resistance, or in a resonant circuit, the current and voltage are in phase and Z is purely resistive. In a circuit containing only reactance the current and voltage are out of phase and Z is purely imaginary, i.e. there is no dissipation in the circuit.
The complex impedance is the ratio of the complex voltage to the complex current, given respectively as
$V = V_{o} exp [j (ω t + ϕ)]$
$I = I_{o} exp (jω t)$
Hence the complex impedance can be expressed as
$Z = | Z | exp (j ϕ)$
$Z = | Z | (cosϕ + j sinϕ)$
2. See impedor.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imped.html An introduction to impedance, from Georgia State University

单词	impedance
释义	impedance Physics Symbol Z. The quantity that measures the opposition of a circuit to the passage of a current and therefore determines the amplitude of the current. In a d.c. circuit this is the resistance (R) alone. In an a.c. circuit, however, the reactance (X) also has to be taken into account, according to the equation: Z²=R²+X², where Z is the impedance. The complex impedance is given by Z=R+iX, where i=√−1. The real part of the complex impedance, the resistance, represents the loss of power according to Joule’s law. The ratio of the imaginary part, the reactance, to the real part is an indication of the difference in phase between the voltage and the current. Electronics and Electrical Engineering 1. (symbol: Z; unit: ohm) A measure of the response of an electric circuit to an alternating current. The current is opposed by the capacitance and inductance of the circuit in addition to the resistance. The total opposition to current flow is the impedance, which is given by the ratio of the voltage to the current in the circuit. The alternating current is given by $I = I_{o} cosω t$ where I_o is the peak current and ω is the angular frequency. When reactance, due to the capacitance and inductance, is present in a circuit, the voltage will be out of phase with the current and is given by $V = V_{o} cos (ω t + ϕ)$ where ϕ is the phase angle. In a circuit containing resistance, R, capacitance, C, and inductance, L, the voltage is given by $V_{o} cos (ω t + θ) = I R + L (\frac{d I}{d t}) + \frac{1}{C} \int^{} I d t$ Solving this equation shows that the current is equal to $I = \frac{V_{o} cos (ω t + ϕ)}{\sqrt{[R^{2} + (ω^{2} L^{2} - \frac{1}{ω^{2} C^{2}})]}}$ Since the impedance is the ratio of current to voltage then $Z = \sqrt{[R^{2} + (ω^{2} L^{2} - \frac{1}{ω^{2} C^{2}})]} = \sqrt{[R^{2} + X^{2}]}$ where X is the reactance. Z is thus a complex quantity whose magnitude or modulus \|Z\| is equal to the vector sum of R and X. The complex impedance can thus be given by $Z = R + j X$ where j is equal to √–1. The real part, the resistance, represents a loss of power due to dissipation. The imaginary part, the reactance, indicates the phase difference between the voltage and current (see j). It is either positive or negative depending on whether the current lags or leads the voltage, respectively. In a circuit containing only resistance, or in a resonant circuit, the current and voltage are in phase and Z is purely resistive. In a circuit containing only reactance the current and voltage are out of phase and Z is purely imaginary, i.e. there is no dissipation in the circuit. The complex impedance is the ratio of the complex voltage to the complex current, given respectively as $V = V_{o} exp [j (ω t + ϕ)]$ $I = I_{o} exp (jω t)$ Hence the complex impedance can be expressed as $Z = \| Z \| exp (j ϕ)$ $Z = \| Z \| (cosϕ + j sinϕ)$ 2. See impedor. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imped.html An introduction to impedance, from Georgia State University
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