Physical concepts current electricity

Understanding electrochemical instrumentation requires a basic knowledge of electricity and basic electronics. Coverage of these fundamentals is impossible in a text of this size. The student is advised to review the concepts of electricity learned in general physics, and to understand the definitions of current, voltage, resistance, and similar basic terms. The texts by Kissinger and Heineman, Malmstadt et al., or Diefenderfer and Holton, listed in the bibliography, are excellent sources of information on electronics used in instrumentation. The electrochemical cell is one circuit element with specific electrical properties in the complete instrumentation circuit. 

The method of approach will be akin to that used in the analysis of electrical networks where current to and from nodes and along individual circuit branches can be calculated. In fact, a principal purpose of this chapter will be to introduce the concepts of electrical network circuit analysis to the study of diffusion mechanisms. The physical picture to which this discussion will relate throughout the chapter is that for self-diffusion in a crystallogra-phically perfect, homogeneous material. Thus, no attention will be given to grain boundary or surface diffusion. 

The concept of quantization enabled physicists to solve problems that nineteenth-century physics could not. One of these involved the thermal properties of solids when they are heated to incandescence. The other involved the induction of electrical current in metals when they are exposed to only specific frequencies of electromagnetic radiation. 

The present chapter is devoted mainly to one of these new theories, in particular to its possible applications to photon physics and optics. This theory is based on the hypothesis of a nonzero divergence of the electric field in vacuo, in combination with the condition of Lorentz invariance. The nonzero electric field divergence, with an associated space-charge current density, introduces an extra degree of freedom that leads to new possible states of the electromagnetic field. This concept originated from some ideas by the author in the late 1960s, the first of which was published in a series of separate papers [10,12], and later in more complete forms and in reviews [13-20]. 

Apart from the large number of areas of knowledge associated with modem electrochemistry, there are many areas to which it contributes or in which it plays an essential role. Thus, much surface chemistry under real conditions involves moisture hence the electrified interfaces for which electrochemical concepts are relevant are as wide in application as practical surface chemistry itself. This, together with the fact that the subject embraces interactions between electric currents and materials (i.e between two large areas of physics and chemistry), implies a widespread character for the phenomena subject to electrochemical considerations (Fig. 1.8). 

However, particulate meanings, especially the concept of transfer of electrons, appear not to be easy for students to understand. Transfer of etectrons looks like transport of electrons, a familiar concept for many students due to prior physics lessons. The way by which half reaction equations are written suggests that transfer of electrons is the same as the transport of electrons from one place (reductant) to another place (oxidant). For that reason, students may expect that in the classic school experiment, when the iron nail is put in a solution of copper sulphate, an electrical current will be indicated. However, teachers do not pay attention to efforts to check if an electrical current will take place. For students, this omission may exacerbate the difficulties in accepting the concept of an electron shift. 

Numerous models have been proposed for hopping transport (see e.g. [Ml], [M2]). Conceptionally the simplest and physically most well-founded is the model of Bassler [47], which we will outline in the next section. In the sections thereafter, we will present typical experimental results for the temperature and electric-field dependencies of the mobility and for the temperature, field and thickness dependence of the dark current I(V) as a function of the applied voltage in disordered organic semiconductors. 

Hart, C. (2002). Framing curriculum discursively Theoretical perspectives on the experience of VCE Physics. International Journal of Science Education, 24 (10), 1055-1077. Koumaras P., Kariotoglou, P. Psillos, D. (1997) Causal structures and counter-inmitive experiments in electricity. International Journal of Science Education, 19 (6), 617-630. Mulhall, P., McKittrick. B. Gunstone, R. (2001). A perspective on the resolution of confusions in the teaching of electricity. Research in Science Education, 31 (4), 575-587. Pordhan, H., Bano, Y. (2001) Science teachers alternate conceptions about direct-currents. 

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