Enlighten The Phenomenon Of Electromotive Force ?
In order to maintain an electric current, some agency is required to expend energy in moving the charge around a circuit. With the exception of a few metals near absolute zero, the superconductors, all conductors present some opposition to the flow of charge so that work must be done to maintain a current. An agency capable of causing such a flow by converting other forms of energy to electrical work is called a seat of electromotive force or a source of current. It should be clearly understood that a source of current does not manufacture charge but merely moves the charge through a circuit. In most circuits this agency is concentrated in one or a few parts of this agency is concentrated in one or a few pats of the circuit. The source must create an electric field in all parts of the circuit to cause the charges to move against the various opposing effects they may encounter. The electromotive force, or emf, of a source is the energy per unit charge transformed in a reversible process. (The term “electromotive force” is an old term now rooted in the language of physics; its choice was unfortunate, as this quaintly is not a force. Hence its abbreviation emf will be used hereafter.) In the mks system, emf will be used hereafter).An emf causes difference of potential to exist between points in the circuit. Thus there is an intimate relation between emf and potential difference. An emf associated only with reversible conversions of energy, whereas potential difference exists not only in source of emf but also in resistors, which convert energy to heat irreversibly. The distinction is sometimes useful and will becomes clearer as we proceed.In the simple circuit charge flow through the circuit, the cell converts chemical energy to electrical energy, giving rise to an emf. The lamp is a resistive conductor called a resistor; it converts electric energy to heat, and work done on the charge by the electric field, as the charge moves through the resistor, is evidenced by the presence of a potential difference between the ends of the resistor. A small amount of the total electric energy converted from chemical energy in the cell also produces heat inside the cell. Electric circuits are conventionally reprinted by circuit diagrams employing standard symbols.
