Basic DC Theory
DC CIRCUIT ANALYSIS
Third, apply Kirchhoff’s voltage law to loops one and two by picking a point in each loop and
writing a loop equation of the voltage drops around the loop; then set the equation equal to zero.
Figure 40 Applying Voltage Law to Loop 1
Figure 40 shows Loop one.
From Point A to Point B, there is an increase in voltage of 8 volts. From Point C to Point D,
there is an increase in voltage of 200 (I2 - I1). From Point D to Point E, there is a decrease in
voltage of 10 volts. From Point E to Point A, there is a voltage decrease of 50I1 volts. The
result in equation form is illustrated in equation (2-16).
8 + 200 (I2 - I1) - 50 I1 - 10 = 0
(2-17)
Using the same procedure for Loop 2 of Figure 39, the resulting equation is shown in equation
(2-18).
10 - 200 (I2 - I1) + 40 - 100 I2 = 0
(2-18)
Fourth, solve equations (2-17) and (2-18) simultaneously. First, rearrange and combine like terms
in the equation for Loop 1.
-50 I1 + 200 I2 - 200 I1 = 10 - 8
-250 I1 + 200 I2 = 2
Divide both sides by two.
-125 I1 + 100 I2 = 1
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