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The International System of Electrical and Magnetic Units is an obsolete system of units used for measuring electrical and magnetic quantities. It was proposed as a system of practical international units (e.g., the international ampere, the international ohm, the international volt) by unanimous recommendation at the International Electrical Congress (Chicago, 1893), discussed at other ...
where is the magnetic force constant from the Biot–Savart law, / is the total force on either wire per unit length of the shorter (the longer is approximated as infinitely long relative to the shorter), is the distance between the two wires, and , are the direct currents carried by the wires. This is a good approximation if one wire is ...
Without the presence of an electric field, the electrons have no net velocity. When a DC voltage is applied, the electron drift velocity will increase in speed proportionally to the strength of the electric field. The drift velocity in a 2 mm diameter copper wire in 1 ampere current is approximately 8 cm per hour. AC voltages cause no net movement.
The numbers of wire were in common use earlier than 1735 when the measurements were officially defined. [1] It is believed that they originally were based on the series of drawn wires, No. 1 being the original rod, and succeeding numbers corresponding with each draw, so that No. 10, for example, would have passed ten times through the draw plate.
By combining the Lorentz force law above with the definition of electric current, the following equation results, in the case of a straight stationary wire in a homogeneous field: [30] =, where ℓ is a vector whose magnitude is the length of the wire, and whose direction is along the wire, aligned with the direction of the conventional current I.
One volt is defined as the electric potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points. [2] It can be expressed in terms of SI base units ( m , kg , s , and A ) as
The phase velocity at which electrical signals travel along a transmission line or other cable depends on the construction of the line. Therefore, the wavelength corresponding to a given frequency varies in different types of lines, thus at a given frequency different conductors of the same physical length can have different electrical lengths.
For example, the United States National Electrical Code, Table 310.15(B)(16), specifies that up to three 8 AWG copper wires having a common insulating material (THWN) in a raceway, cable, or direct burial has an ampacity of 50 A when the ambient air is 30 °C, the conductor surface temperature allowed to be 75 °C. A single insulated conductor ...