An ideal voltage sources are an electric device that generates a prescribed voltage at its terminals. The ability of an ideal voltage source to generate its output voltage is not affected by the current it must supply to the other circuit elements.
Note that the output voltage of an ideal source can be a function of time.
The notion of an ideal voltage source is best appreciated within the context of the source-load representation of electric circuits. below Figure depicts the connection of an energy source with a passive circuit (i.e., a circuit that can absorb and dissipate energy). Three different representations are shown to illustrate the conceptual, symbolic, and physical significance of this source-load idea.
An ideal voltage source provides a prescribed voltage across its terminals
irrespective of the current flowing through it. The amount of current supplied by the source is determined by the circuit connected to it.
The i-v characteristics of ideal current and voltage sources can also be useful in visually representing their behavior. An ideal voltage source generates a prescribed voltage independent of the current drawn from the load; thus, its i-v characteristic is a straight vertical line with a voltage axis intercept corresponding to the source voltage. Similarly, the i-v characteristic of an ideal current source is a horizontal line with a current axis intercept corresponding to the source current. below Figure depicts these behaviors
When electric current flows through a metal wire or through other circuit elements,it encounters a certain amount of resistance, the magnitude of which depends on the electrical properties of the material. Resistance to the flow of current may be undesired—for example, in the case of lead wires and connection cable
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FUNDAMENTALS OF ELECTRICAL ENGINEERING for Giorgio Rizzoni