Applied voltage changes

The colors shown in Table 6.1 are only approximate. Sometimes mixtures of colors are seen as gas pressure or applied voltages change or if impurities are present. 

The value of dS/dE was considered. If the applied voltage changes by E, the whole discharge space must reach the sparking potential once. Accordingly, the discharge also occurs once. Hence, dS/dE = S/E is obtained, where S is the total discharge area. 

This relation is of considerable practical importance because it justifies the fact that the response of the electrochemical system varies as the polarity of the applied voltage changes. Admitting that the two electrodes present different corrosion rates, Id and 7 2 > and applying the linear approximation of the formula (4 ), we obtain the expression... 

The exact conditions of gas pressure, current flow, and applied voltage under which the discharge occurs determine if it is of the corona, plasma, or arc type. The color of the emitted light may also change, depending not only on the type of gas used but also on whether it is a corona, plasma, or arc discharge. 

Amperometry refers to measurement of current under a constant applied voltage and under these conditions it is the concentration of the analyte which determines the magnitude of the current. Such measurements may be used to follow the change in concentration of a given ion during a titration, and thus to fix the end point this procedure is referred to as amperometric titration. 

Electric field sensitive dyes respond to changes in electrical membrane potential by a variety of different mechanisms with widely varying response times depending on their chemical structure and their interaction with the membrane. An understanding of the mechanisms of dye response and their response mechanisms is important for an appropriate choice of a probe for a particular application. The purpose of this chapter is, therefore, to provide an overview of the dyes presently available, how they respond to voltage changes, and give some examples of how they have been applied. Finally, because there is still scope for the development of new dyes with improved properties, some directions for future research will be discussed. 

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