Unit 15 Alternating Current. Objectives: Discuss differences between direct and alternating current. Be able to compute instantaneous values of voltage and current for a sine wave. Be able to compute peak, RMS, and average values of voltage and current.
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Alternating current flows first in one direction and then in the other direction.
A graph view of a square wave.
A square wave alternating current produced by a switch and two batteries.
The sine wave is the most common of all the AC wave forms.
The sine wave is produced by rotating machines.
One sine wave is 360 electrical degrees.
The voltage at any point along the sine wave is equal to the maximum, or peak, value times the sine of the angle of rotation.
As the loop approaches 90° of rotation, the fluxlines are cut at a faster rate.
E(INST) = E(MAX) x SINE θ
E(INST) = the voltage at any point on the wave form
E(MAX) = the maximum, or peak, voltage
SINE θ = the sine of angle theta, the angle of rotation
Instantaneous values of voltage along a sine wave.
Peak, Peak-to-Peak,and RMS valuesalong a sine wave.
RMS = Peak x 0.707
Peak = RMS x 1.414
In a pure resistive circuit, the voltage and current are in phase.