later time (to the right of the time axis) is said to lag the

other wave.

m. *Ohm's Law In AC Circuits*. Many ac circuits contain

resistance only. The rules for these circuits are the same

rules that apply to de circuits. Resistors, lamps, and heating

elements are examples of resistive elements. When an .ac

circuit contains only resistance, Ohm's Law, Kirchhoff's Law,

and the various rules that apply to voltage, current, and power

in a dc circuit also apply to the ac circuit. The Ohm's Law

formula for an ac circuit can be stated as

Eeff E

Ieff = or I =

R R

Remember, unless otherwise stated, all ac voltage and current

values are given as effective values. The formula for Ohm's Law

can also be stated as

Eavg Emax

Iavg = or Imax = or

R R

Epeak-to-peak

Ipeak-to-peak =

R

The important thing to keep in mind is: DO NOT mix ac values.

When you solve for effective values, all values you use in the

formula must be effective values. Similarly, when you solve for

average values, all values you use must be average values.

This point should be clearer after you work the following

problem: A series circuit consists of two resistors (R1 = 5 Ohms

and R2 = 15 Ohms) and an alternating voltage source of 120

volts. What is Iavg?

Given:

R1 = 5 Ohms

R2 = 15 Ohms

Es = 120 volts

RT R1 + R2

RT 5 Ohms + 15 Ohms

RT = 20 Ohms

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