Elements of Electric Circuits

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Elements of Electric Circuits
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Simple electric circuits
load
source
By convention, positive current flows out of the
positive terminal
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Ideal Voltage sources provides defined voltage
(electromotive forceEMF) on its terminals.
Corresponding current is defined by the circuit
connected to it.
Symbols for ideal voltage sources
Symbols for ideal current sources
Ideal Current sources provides defined current to
any load connected to it. Corresponding voltage
is determined by the load
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Branch is a portion of circuit between two
terminals. Also, every circuit element with two
terminals may be a branch.
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Nod is a junction of two (trivial node) or more
branches
Loops
A Loop is any closed connection of branches.
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A Mesh is a simple loop, that does not contain
other loops. Meshes are easy to observe in more
complex networks.
mesh1
A loop may contain many meshes. Mesh contains
only one loop.
mesh3
mesh2
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Network analysis To solve a network means to
determine all unknown brunch currents and all
unknown node voltages. Networks are solved
utilizing Current and Voltage Kirchhoffs Laws.
Current Kirchhoffs LawConservation of charges
Electric charges cant be produced and cant be
lost (They can only be generated, for instance by
chemical process, by oxidation and reduction, by
splitting molecules into ions).
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The sum of currents at one nod must be zero. The
charges that enter the nod at one place, exit at
another.

Current Kirchhoffs Law
Ib
I1
I2
Vb
I3
Example If your car battery is to supply the fan
with 2A, locks with 1A and headlights with 6A,
calculate the current of the battery.
-IbI1I2I30
IbI1I2I39A
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Kirchhoffs Voltage law (Conservation of energy)
Net voltage around a closed loop must be zero.
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Mechanical analogy
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Sign Convention
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When to use Kirchhoff's laws