LRC Circuits - 5/6/09

Today in class we had lots of fun with oscilloscopes and LRC circuits. If you haven't looked at Mason's AC circuits notes, I highly suggest you do or you might internally combust due to massive confusion. Mason's notes really helped me understand the vector problems in the HW.

We took a good look at phase angles and how to caluclate them and what they mean. Basically when looking at both current and voltage in an oscilloscope, current and voltage will both oscillate sinusoidally but not at the same time. The difference in which the current leads or lags the voltage is called the phase angle.

Phase angle (phi) = tan(-1)(XL-XC)/R = 2pi*delta t/T(dr)

Where T(dr) = the period of oscillcation of the driving emf.

Since it has been almost 10 years since I had to figure out the period of a function, I spent the entire class asking myself WTF? So it also might be really useful to know how to find the period;

Period(T) = 1/f
w=2*pi*f

We briefly went over the Root Mean Square Current and Voltage. Mason proved that the average current and voltage on always equal to zero, but the average power of the AC circuit is not equal to zero....ya we've all been zapped by AC circuit.

In general, your equations of Voltage and Current will look something like this for a LRC AC circuit in series;

If circuit is voltage diriven;

V(f)= Vmax*sin(wt)
I(f)= Imax*sin(wt-phi)
phi = phase angle

If circuit is current driven.

I(f)= Imax*sin(wt)
V(f)= Vmax*sin(wt-phi)

The circuit will still obey Kirchoff's rules.

Good luck on all of the H-dub!!