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Kirchhoff’s Laws
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Kirchhoff’s Current Law
Kirchhoff’s Voltage Law
Series Circuits
Parallel Circuits
Polarity
Kirchhoff’s Current Law
Key Point:
The number of charges per
second (current) flowing to
a point in a conductor must
equal the number of charges
flowing from that point.
(See Figure 10-35.)
Kirchhoff’s Voltage Law
Key Point: Around any
closed path, the sum of
potential rises must equal the
sum of potential drops.
ΣE = ΣV.
E=V1+V2
Series Circuits
Key Point:
In a series circuit:
(1) the current is the same IT = I1 = I2 = IN
throughout the circuit;
(2) the sum of the voltage
E = V1+V2+…+VN
drops must equal the
emf
Parallel Circuits
Key Point:
In a parallel circuit:
(1) the voltage drop is the
V1 = V2 = VN
same across each
branch;
(2) the total current into
and out of the branches IT = I1+I2+…+IN
equals the sum of the
individual branch
currents.
Polarity
Key Point:
In an electrical circuit
the polarity of the
voltage drops across
the individual
resistances depends on
the direction of current
through them.
(See Figure 10-36.)