00:01
So a system that mimics a mass on a spring with damping is the rlc siri circuit.
00:09
And here we're going to investigate what it means for this circuit to resonate.
00:15
First of all, we can draw on a phaser diagram.
00:20
And remember, what we are doing with the x -axis is we are looking at things that are in phase with the driving.
00:31
Ac driving, so whether that's a cosine or a sign, that x -axis will represent the cosine, for example.
00:39
And the y -axis will represent the sign.
00:44
So the two phases are 90 degrees apart.
00:49
And if we draw the generalized resistances on the phaser diagram, the resistor has reactants, if you well that lies along the axis that goes with the driving term, which means that the current in that resistor is always in phase with the drive through the resistor.
01:18
On the y -axis, we show the inductive reactants, sorry, xl, and that is equal to omega -l.
01:34
The capacitive reactants, the however, points downwards.
01:40
So 1 over omega -c is equal to the capacitive reactants.
01:46
And the currents in both of those either lead or lag the voltage source by 90 degrees.
01:56
So what we mean by resonance is a couple things.
02:01
The first step is to recognize that you can have the capacitive reactants equal the inductive reactants.
02:11
And that will fix the resonance frequency.
02:19
Okay, when those two things are equal to each other.
02:25
And then we can actually solve for what that frequency is.
02:29
One over omega -c is the capacitive reactants.
02:33
Omega -l is the inductive reactants.
02:37
And solving for omega, it turns out that the resonance frequency is one over the square root of l times c.
02:51
And it's also equal to 2 pi times the resonance frequency in hertz, omega being angular frequency.
03:05
So for this circuit, we can actually calculate what that resonance frequency is.
03:10
We have 13 millie henry, 13 times 10 to the minus 3, in si units and 0 .2 milli -faird...