Chapter 20
Circuits and Direct Currents
By Boundless
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An electrical circuit is an interconnection of electrical elements that has a closed loop giving a return path for the current.
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Electromotive force (EMF) is the voltage voltage generated by a battery or by the magnetic force according to Faraday's Law of Induction.
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The total resistance in the circuit with resistors connected in series is equal to the sum of the individual resistances.
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The total resistance in a parallel circuit is equal to the sum of the inverse of each individual resistances.
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A combination circuit can be broken up into similar parts that are either series or parallel.
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When voltage sources are connected in series, their emfs and internal resistances are additive; in parallel, they stay the same.
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The output, or terminal voltage of a voltage source such as a battery, depends on its electromotive force and its internal resistance.
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Kirchhoff's circuit laws are two equations that address the conservation of energy and charge in the context of electrical circuits.
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Kirchhoff's junction rule states that at any circuit junction, the sum of the currents flowing into and out of that junction are equal.
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Kirchhoff's loop rule states that the sum of the emf values in any closed loop is equal to the sum of the potential drops in that loop.
![Thumbnail](../../../../../figures.boundless-cdn.com/16800/square/figure-22-03-05.jpeg)
Kirchhoff's rules can be used to analyze any circuit and modified for those with EMFs, resistors, capacitors and more.
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An RC circuit has a resistor and a capacitor and when connected to a DC voltage source, and the capacitor is charged exponentially in time.
![Thumbnail](../../../../../figures.boundless-cdn.com/30798/raw/ter-28with-v-26i-labels-29.jpg)
Impedance is the measure of the opposition that a circuit presents to the passage of a current when a voltage is applied.
![Thumbnail](../../../../../figures.boundless-cdn.com/17352/raw/ter-28with-v-26i-labels-29.jpg)
In a series RC circuit connected to an AC voltage source, voltage and current maintain a phase difference.