Most practical applications of electricity involve the flow of electric current in a closed path under the influence of a driving voltage, analogous to the flow in a water circuit under the influence of a driving pressure. A complete path, typically through conductors such as wires and through circuit elements, is called an electric circuit.
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|Steady-state direct current circuits with batteries and resistors only|
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|b) Transients in RC circuits|
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An electric circuit is a conducting path, external to the battery, which allows charge to flow from one terminal to the other. A simple circuit might consist of a single strand of metal wire linking the positive and negative terminals. A more realistic circuit possesses multiple branch points, so that charge can take many different paths between the two terminals.
Suppose that a (positive) charge q is driven around the external circuit, from the positive to the negative terminal, by the electric field set up between the terminals. The work done on the charge by this field during its journey is qV, where V is the difference in electric potential between the positive and negative terminals. We usually refer to as the voltage of the battery: e.g., when we talk of a 6 volt battery, what we actually mean is that the potential difference between its two terminals is 6 V.