k. *Sine Waves in Phase*. When a sine wave is applied to a

resistance, the resulting current is also a sine wave. This

follows Ohm's law which states that current is directly

proportional to the applied voltage. Now examine figure 68.

Notice that the sine wave of voltage and the resulting sine wave

of (current are superimposed on the same time axis. Notice also

that as the voltage increases in a positive direction, the

current increases along with it, and that when the voltage

reverses direction, the current also reverses direction. When

two sine waves, such as those represented in figure 68, are

precisely in step with one another, they are said to be IN

PHASE. To be in phase, the two sine waves must go through their

maximum and minimum points at the same time and in the same

direction.

FIGURE 68. VOLTAGE AND CURRENT WAVES IN PHASE.

In some circuits, several sine waves can be in phase with each

other. Thus, it is possible to have two or more voltage drops

in phase with each other and also be in phase with the circuit

current.