Welcome back. 
So far we have finished Modules 1, 2, and 
3, and we're starting Module 4 on 
Frequency Analysis. 
Previously, I've tried to show you the 
difference between Resistive and Reactive 
Circuits, so you, to motivate you why we 
would want to study both of those 
circuits. 
Last time, I showed this plot. 
I showed the response of the resisted 
circuit to a square wave. 
Now, this shows a physical circuit. 
This is a screenshot from an oscilloscope 
and this is a resistive network. 
The voltage source is a sign wave and the 
response across any of the resistors is 
also a sign wave. 
Now, both of these measure voltage versus 
time. 
Notice that the zero crossings, right 
here, the zero crossings all line up and 
that's typical with resistant circuits. 
If I bring up a reactive circuit, so the 
voltage source is in green and the 
response across any of the elements in 
that circuit is in blue. 
Notice how there is a lag in this. 
The response does not exactly line up 
with the input and that's typical of a 
reactive circuit. 
And it also makes it a lot more 
interesting and useful when we want to do 
practical applications like filtering. 
So the basic concept I want you to 
understand in here is that if I put in a 
sign wave to a circuit, whether a linear, 
whether a resistant circuit or reactive 
circuit, I'm going to get a sign wave 
out. 
With the reactive circuits, there's going 
to be a time delay, or lag in the 
circuit. 
In both cases, the output might change 
the amplitude, so there might be a git 
different in the amplitude from the input 
to the output of this circuit. 
And then again in the reactive circuit, 
there's also a time delay. 
Going back to our concept map on 
frequency analysis. 
We will be pulling forward, the ideas and 
analysis that we've already performed for 
RC and RLC circuits from the reactive 
circuit module from the resistive circuit 
module. 
We're going back to those methods to 
obtain circuit equations, so those same 
tools, those strategies. 
The KCL, the KVL, the mesh, node, and 
Thevenin equivalents, we will again use 
in frequency analysis. 
The particular topics that will cover are 
going to include an introduction to 
frequency domain, impedances, which are 
simply complex resistances, AC circuit 
analysis Transfer functions, frequency 
response with the application to 
filtering.