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The volt-ampere (SI symbol: VA, [1] sometimes V⋅A or V A) is the unit of measurement for apparent power in an electrical circuit. It is the product of the root mean square voltage (in volts) and the root mean square current (in amperes). [2] Volt-amperes are usually used for analyzing alternating current (AC) circuits.
Symbol [1] Name of quantity Unit name Symbol Base units E energy: joule: J = C⋅V = W⋅s kg⋅m 2 ⋅s −2: Q electric charge: coulomb: C A⋅s I electric current: ampere
The ampere-turn (symbol A⋅t) is the MKS (metre–kilogram–second) unit of magnetomotive force (MMF), represented by a direct current of one ampere flowing in a single-turn loop. [1] Turns refers to the winding number of an electrical conductor composing an electromagnetic coil .
is the motor torque constant (SI unit, newton–metre per ampere, N·m/A), see below If two motors with the same K v {\displaystyle K_{\text{v}}} and torque work in tandem, with rigidly connected shafts, the K v {\displaystyle K_{\text{v}}} of the system is still the same assuming a parallel electrical connection.
In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. [1] The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space, its direction being that of the motion of the positive charges at this point.
The ampere is an SI base unit and electric current is a base quantity in the International System of Quantities (ISQ). [4]: 15 Electric current is also known as amperage and is measured using a device called an ammeter. [2]: 788 Electric currents create magnetic fields, which are used in motors, generators, inductors, and transformers.
As of the 2019 revision of the SI, the ampere is defined by fixing the elementary charge e to be exactly 1.602 176 634 × 10 −19 C, [6] [9] which means an ampere is an electric current equivalent to 10 19 elementary charges moving every 1.602 176 634 seconds or 6.241 509 074 × 10 18 elementary charges moving in a second.
When it came to deriving the electromagnetic wave equation from displacement current in his 1865 paper 'A Dynamical Theory of the Electromagnetic Field', he got around the problem of the non-zero divergence associated with Gauss's law and dielectric displacement by eliminating the Gauss term and deriving the wave equation exclusively for the ...