Through the use of Kirchhoff's law, circuit

problems can be solved which

would be difficult, and often impossible, with

knowledge of Ohm's law alone.

When Kirchhoff's law is properly applied, an

equation can be set up for a

closed loop and the unknown circuit values can

be calculated.

e. *Polarity of Voltage. * To apply Kirchhoff's voltage law, the meaning

of voltage polarity must be understood. In the circuit shown in figure 27,

the current is shown flowing in a counterclockwise direction. Notice that

the end of resistor R1, into which the current flows, is marked negative

(-). The end of R1, at which the current leaves, is marked positive (+).

These polarity markings are used to show, that the end of R1, into which the

current flows is at a higher negative potential than the end of the resistor

at which the current leaves. Point A is more negative than point B.

Point C, which is at the same potential as point B, is labeled negative.

This is to indicate that point C is more negative than point D. To say a

point is positive (or negative) without stating what the polarity is based

upon has no meaning. In working with Kirchhoff's law, positive and negative

polarities are assigned in the direction of current flow.

FIGURE 29.

VOLTAGE POLARITIES.