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The electrical resistance of a uniform conductor is given in terms of resistivity by: [40] = where ℓ is the length of the conductor in SI units of meters, a is the cross-sectional area (for a round wire a = πr 2 if r is radius) in units of meters squared, and ρ is the resistivity in units of ohm·meters.
The equivalent voltage V th is the voltage obtained at terminals A–B of the network with terminals A–B open circuited. The equivalent resistance R th is the resistance that the circuit between terminals A and B would have if all ideal voltage sources in the circuit were replaced by a short circuit and all ideal current sources were replaced ...
A legal ohm, a reproducible standard, was defined by the international conference of electricians at Paris in 1884 as the resistance of a mercury column of specified weight and 106 cm long; this was a compromise value between the B. A. unit (equivalent to 104.7 cm), the Siemens unit (100 cm by definition), and the CGS unit. [13]
The SI unit of electrical resistivity is the ohm-metre (Ω⋅m). [1] [2] [3] For example, if a 1 m 3 solid cube of material has sheet contacts on two opposite faces, and the resistance between these contacts is 1 Ω, then the resistivity of the material is 1 Ω⋅m.
In electrical engineering, impedance is the opposition to alternating current presented by the combined effect of resistance and reactance in a circuit. [1]Quantitatively, the impedance of a two-terminal circuit element is the ratio of the complex representation of the sinusoidal voltage between its terminals, to the complex representation of the current flowing through it. [2]
Also called chordal or DC resistance This corresponds to the usual definition of resistance; the voltage divided by the current R s t a t i c = V I. {\displaystyle R_{\mathrm {static} }={V \over I}.} It is the slope of the line (chord) from the origin through the point on the curve. Static resistance determines the power dissipation in an electrical component. Points on the current–voltage ...
Figure 4. These circuits are equivalent: (A) A resistor at nonzero temperature with internal thermal noise; (B) Its Thévenin equivalent circuit: a noiseless resistor in series with a noise voltage source; (C) Its Norton equivalent circuit: a noiseless resistance in parallel with a noise current source.
The siemens (symbol: S) is the unit of electric conductance, electric susceptance, and electric admittance in the International System of Units (SI). Conductance, susceptance, and admittance are the reciprocals of resistance, reactance, and impedance respectively; hence one siemens is equal to the reciprocal of one ohm (Ω −1) and is also referred to as the mho.