Now we'll be starting Module 3. Going back to our concept map, we have
finished the background module, the module on resistive circuits and now
we're starting the module on reactive circuits.
I'd like to stop and give you some background or some way of comparing
resistive circuits to reactive circuits to teach you or motivate you why we
want to study reactive circuits, and how it differs from resistive circuits.
To do that, I'm going to show a experimental result.
This is a display from an oscilloscope. Oscilloscope is a measuring device that
shows voltages. Along the horizontal axis is time.
So each division is a division in time. This particular one is milli-, in
milliseconds, 1 millisecond [UNKNOWN] per division.
The vertical axis is voltage. The green line shows the voltage source
to resistive network. And in this case, it's going up and down.
So here, it's at 1 volt, and then it goes down to minus 1 volt for 2.5
milliseconds. Then it goes up to plus 1 volt and then
back down to minus 1 volt. This is what's called the square wave.
The blue line is the voltage across one of the resistors in that circuit.
Notice how the voltage across the resistor is exactly in line and looks
exactly the same as the voltage source except for the fact that it's scaled.
And that's what it happens in a static circuit.
The voltage output exactly matches the form, the shape of the voltage input.
Now, a reactive circuit is different. In a reactor circuit, I've got, in this
particular case, a capacitor in there. The voltage source looks the same but the
response across any of the elements in that circuit looks different.
It doesn't exactly match the shape. It's got some.
Behavior to it. So this is equivalent, let's say in a
physical system, having an object, a physical object.
And it's got object, it's got inertia to it.
And we want to push that object up to a certain speed.
Well it takes you a while to get up to speed.
And that's equivalent to what's happening here.
It takes it a while to get up to the, the correct voltage.
It doesn't happen instantaneously. And that's the difference between a
resistive and a reactive circuit. And that basic behavior allows us to do a
lot of very interesting designs in our circuit, so it has a lot of interesting
behaviors. So, it's important for us to understand
those behaviors. And to understand those behaviors, we're
going to have to look at differential equations.
And we'll give you some very basic background in differential equations
during this module. Bringing back up the concept map.
We've done the background in resistive circuits, and we're pulling some of those
concepts forward into the reactive circuit module.
In particular, the definitions of current and voltage, voltage sources, and current
sources, and resistance were pulling forward from the background module.
From the resistive circuit module, We're going to be utilizing those methods to
obtain circuit equations. That includes Kirchhoff's Current Law,
Kirchhoff's Voltage Law, mesh, node, and Thevenin equivalence.
Everyone of those methods that we've already used are pertinent to the
reactive circuits. The particular concepts we're going
through in reactive circuits are capacitors and inductors, differential
equations and I'm not assuming that you know differential equations by now.
I'm only going to be using enough material to introduce to how to solve RC
circuits and RL circuits.