Chapter
Kirchhoff’s Laws
Topics Covered in Chapter 9
9-1: Kirchhoff’s Current Law (KCL)
9-2: Kirchhoff’s Voltage Law (KVL)
9-4: Node-Voltage Analysis
9-5: Method of Mesh Currents
9
9-1: Kirchhoff’s Current Law (KCL)
 The sum of currents
entering any point in a
circuit is equal to the sum of
currents leaving that point.
 Otherwise, charge would
accumulate at the point,
reducing or obstructing the
conducting path.
 Kirchhoff’s Current Law may
also be stated as
IIN = IOUT
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Fig. 9-1: Current IC out from point P
equals 5A + 3A into P.
9-2: Kirchhoff’s Voltage Law (KVL)
 Loop Equations
 A loop is a closed path.
 This approach uses the algebraic equations for the
voltage around the loops of a circuit to determine the
branch currents.
 Use the IR drops and KVL to write the loop
equations.
 A loop equation specifies the voltages around the
loop.
9-2: Kirchhoff’s Voltage Law (KVL)
 Loop Equations
 ΣV = VT means the sum of the IR voltage drops must
equal the applied voltage. This is another way of stating
Kirchhoff’s Voltage Law.