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Solar cell output voltage for two light-induced currents I L expressed as a ratio to the reverse saturation current I 0 [52] and using a fixed ideality factor m of 2. [53] Their emf is the voltage at their y-axis intercept. Solving the illuminated diode's above simplified current–voltage relationship for output voltage yields:
E red is the half-cell reduction potential at the temperature of interest, E o red is the standard half-cell reduction potential, E cell is the cell potential (electromotive force) at the temperature of interest, E o cell is the standard cell potential, R is the universal ideal gas constant: R = 8.314 462 618 153 24 J K −1 mol −1, T is the ...
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).
The original design was a saturated cadmium cell producing a 1.018 638 V reference and had the advantage of having a lower temperature coefficient than the previously used Clark cell. [1] One of the great advantages of the Weston normal cell is its small change of electromotive force with change of temperature.
The effective temperature coefficient varies with temperature and purity level of the material. The 20 °C value is only an approximation when used at other temperatures. For example, the coefficient becomes lower at higher temperatures for copper, and the value 0.00427 is commonly specified at 0 °C. [53]
In highly conductive metals the Fermi temperatures are typically around 10 4 – 10 5 K, and so it is understandable why their absolute Seebeck coefficients are only of order 1 – 10 μV/K at room temperature. Note that whereas the free electron model predicts a negative Seebeck coefficient, real metals actually have complicated band ...
However, the corresponding Gibbs free energy changes (∆G°) must satisfy ∆G° = – z FE°, where z electrons are transferred, and the Faraday constant F is the conversion factor describing Coulombs transferred per mole electrons. Those Gibbs free energy changes can be added.
A temperature coefficient describes the relative change of a physical property that is associated with a given change in temperature. For a property R that changes when the temperature changes by dT , the temperature coefficient α is defined by the following equation: