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the preferred realization of the international volt was in terms of the electromotive force of a Weston cell at 20 °C (1.0184 V int), as this type of cell has a lower temperature coefficient than the Clark cell; several other derived units for use in electrical and magnetic measurements were formally defined: [Note 1] International coulomb
When electric charge dQ ele is passed between the electrodes of an electrochemical cell generating an emf, an electrical work term appears in the expression for the change in Gibbs energy: = + +, where S is the entropy, V is the system volume, p is its pressure and T is its absolute temperature.
The electromotive force generated by motion is often referred to as motional emf. When the change in flux linkage arises from a change in the magnetic field around the stationary conductor, the emf is dynamically induced. The electromotive force generated by a time-varying magnetic field is often referred to as transformer emf.
The Seebeck coefficients generally vary as function of temperature and depend strongly on the composition of the conductor. For ordinary materials at room temperature, the Seebeck coefficient may range in value from −100 μV/K to +1,000 μV/K (see Seebeck coefficient article for more information).
Cell diagram. Pt(s) | H 2 (1 atm) | H + (1 M) || Cu 2+ (1 M) | Cu(s) E° cell = E° red (cathode) – E° red (anode) At standard temperature, pressure and concentration conditions, the cell's emf (measured by a multimeter) is 0.34 V. By definition, the electrode potential for the SHE is zero. Thus, the Cu is the cathode and the SHE is the ...
where is back EMF, is the constant, is the flux, and is the angular velocity. By Lenz's law, a running motor generates a back-EMF proportional to the speed. Once the motor's rotational velocity is such that the back-EMF is equal to the battery voltage (also called DC line voltage), the motor reaches its limit speed.
The data below tabulates standard electrode potentials (E°), in volts relative to the standard hydrogen electrode (SHE), at: . Temperature 298.15 K (25.00 °C; 77.00 °F); ...
A positive temperature coefficient (PTC) refers to materials that experience an increase in electrical resistance when their temperature is raised. Materials which have useful engineering applications usually show a relatively rapid increase with temperature, i.e. a higher coefficient.