AC Circuits 12.2

This Week & Next We begin the study of AC Circuits We begin the next unit Friday Same thing Quiz, Of course

2 Problems ???

It’s the current! Note-1: The voltages across each element    i i i Note-1: The voltages across each element are not the same!

The Resistor – A LINEAR Circuit Element Ohm’s Law always applies V=iR In this case:

Phase Diagram

Phase these two voltages have the same amplitude but they do not have these values at the same time! instantaneous voltage leads lags V0 time

Different amplitudes Different Phase Green lags the grey by 90 degrees

Keep In Mind If a circuit has a sinusoidal voltage applied to it the you should expect that all voltages across the various elements will also vary sinusoidally but will have different amplitudes and phase relationships between them

For the Inductor Note that at t=0, DV/Dt is a maximum so back emf is a minimum. From this graph you can see that the current lags the voltage by 90 degrees. A possible relationship between V and I could be V=IXL XL has the units of OHMS and is called the inductive reactance.

Phase Diagram for Inductor More on Inductor Phase Diagram for Inductor The current lags the voltage by 90 degrees.

And so it goes for the Capacitor

Capacitor Circuit Diagram Factoids Note that at t=0, DV/Dt is a maximum so current is also a maximum. From this graph you can see that the current leads the voltage by 90 degrees. A possible relationship between V and I could be V=IXC XC has the units of OHMS and is called the capacitive reactance.

Read in the Textbook

The Approach – Again, Read the Book XL R XC

The Voltages

The Real Deal