PHYS1114 Lecture 18 Alternating CurrentP. 1CH31ALTERNATINGCURRENTIntended Learning Outcomes – after this lecture you will learn:1.To use phasor diagrams to analyze ac circuits2.The response of resistor, inductor and capacitor in an ac circuit3.Power delivery and resonance in anL-R-CcircuitExcluding Session 31.6 Transformers, which you have learned in high school if you have takenHKDSE 1x PhysicsAn alternating current (ac) sourceprovides a sinusoidalvoltage?=?cos??Convention: lower case?is theinstantaneousvalue, whileupper case?is the maximum valueIn HK and most of the world,?= 50 Hz, i.e.,?= 2??=314 /s, whereas in North America,?= 60 HzPeriodof the signal is?= 1?⁄= 2?/?Phasor diagram– represent a sinusoidal signal (e.g.?=?cos??) as a rotating vector in a 2D plane. The projection onthe?axis gives the signalAdvantage:while adding multiple signalsof the same frequency, usevector addition and then project to?axis to get the finalanswer.Avoid drawing multiple sinusoidal graphs.
