KIRCHHOFF’S LAWS Basic DC TheoryApplyingKirchhoff’sVoltageLawFor a simple series circuit, Kirchhoff’s voltage law corresponds to Ohm’s Law. To find thecurrent in a circuit (Figure 33) by using Kirchhoff’s voltage law, use equation (2-15).SE source = SIR (2-15)Figure 33 Using Kirchhoff’s Voltage Law to find Current with one Source80 = 20(I) + 10(I)80 = 30(I)I = 80/30 = 2.66 amperesIn the problem above, the direction of current flow was known before solving the problem.When there is more than one voltage source, the direction of current flow may or may not beknown. In such a case, a direction of current flow must be assumed in the beginning of theproblem. All the sources that would aid the current in the assumed direction of current flow arethen positive, and all that would oppose current flow are negative. If the assumed direction iscorrect, the answer will be positive. The answer would be negative if the direction assumed waswrong. In any case, the correct magnitude will be attained.ES-02 Page 44 Rev. 0
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