ELECTRONIC PRINCIPLES - OD1647 - LESSON 1/TASK 1
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
101
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