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The Idea of Elecric Potential

     In figure. 1 below is shown a simple voltaic cell. it consists of a copper plate (known as anode) and a zinc plate (i.e. cathode) immersed in dilute sulphuric acid (H2SO4) contained insuitable vessel.
Figure 1
the chemical action taking place within the cell causes the electrons to be remove from Cu plate and to be deposited on the zinc plate at the same time. Thsis transfer of electrons is accomplished through the agency of the diluted H2SO4 which is known as electrolyte. The result is that zinc plate becomes negative due to the deposition of electrons on it and the Cu plate becomes positive due to the departure of electrons  from it. The large number of electrons collected on the zinc rod is being attracted by anode, but is prevented from returning to it by the force set up by the chemical action within the cell. But if the two electrodes are joined by wire externally, then electrons rush to the anode, thereby equalizing the charges of the two electrodes. however due to the continuity of chemical action, a continous difference in the number of electrons on the two electrodes is maintened which keeps up a continous flow of current through the external circuit. the action of an electric cell is similar to that of water pump which, while working, maintains acontinous flow of water i.e. water current through the pipe (figure 2).
Figure 2
     It should be particularry noted that the direction of electronic current from zinc to copper in the external circuit. however, the direction of conttional current (which is given by the direction of flow of positive charge) is frim Cu to Zinc. In the present case, there is no flow of positive charge as such from one electrode to another. but we can look upon the arrival of electrons on copper plate (with subsquent decrease in its positive charge) as equivalent to an actual departure of positive charge from it.

(Read also: Modern ElectronTheory)

     When zinc negatively charged it is said to be at negative potential with respect to the electrolyte, whereas anode is said to be at positive potential relative to the electrolyte. Between themselves, Cu plate is assumed to be at a higher potential than the zinc rod. The different in potence in potential is continously maintained by the chemical action going on the cell which supplies energy to establish this potential diffrence. 

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