Effective Value of a Sine Wave.

Electronic Principles
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alternation, the average value of the voltage values occurring

during the complete cycle is zero.

j. Effective Value of a Sine Wave. Emax Eavg, Imax and Iavg are

values used in ac measurements. Another value used is the

EFFECTIVE value of ac. This is the value of alternating voltage

or current that will have the same effect on a resistance as a

comparable value of direct voltage or current will have on the

same resistance.

In an earlier discussion, it was stated that when current flows

in a resistance, heat is produced. When direct current flows in

a resistance, the amount of electrical power converted into heat

equals I2R Watts. However, because an alternating current having

a maximum value of 1 ampere does not maintain a constant value,

the alternating current will not produce as much heat in the

resistance as will a direct current of 1 ampere.

Figure 66 compares the heating effect of 1 ampere of dc to the

heating effect, of 1 ampere of ac.

FIGURE 66. HEATING EFFECT OF AC AND DC.

Examine figure 66; views A and B, and notice that the heat

(70.7 C) produced by 1 ampere of alternating current (that is,

an ac with a maximum value of 1 ampere) is only 70.7 percent of

the heat (100 C) produced by 1 ampere of direct current.