alternating current or voltage completed each second is referred

to as the FREQUENCY. Frequency is always measured and expressed

in Hertz.

Alternatingcurrent frequency is an important term to understand

since most ac electrical equipment requires a specific frequency

for proper operation.

(3) *Period*. An individual cycle of any sine wave represents a

definite amount of time. Notice that figure 61 shows 2 cycles

of a sine wave which has a frequency of 2 Hertz (Hz). Since 2

cycles occur each second, 1 cycle must require onehalf second

of time. The time required to complete one cycle of a waveform

is called the PERIOD of the wave. In the example in figure 61,

the period is onehalf second. The relationship between time

(t) and frequency (f) is indicated by the formulas

1 1

t = and f =

f t

where t = period of time in seconds and

f = frequency in Hertz

FIGURE 61. PERIOD OF SINE WAVE.

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