# Series Parallel Circuits

#### Circuits

Video Lectures created by Tim Fiegenbaum at North Seattle Community College.

Lecture Transcript:
We're in Section 4.4 Series-Parallel Circuits.
These are the third type of circuit that we're looking at in chapter four. Series-parallel connections are another way of connecting electronic components. A series-parallel circuit is a combination of series and parallel components. The series and parallel components must be identified for accurate analysis of the circuit.
To distinguish series vs. parallel components reduced each section to a single resistor series or parallel. If it cannot be reduced, it is a complex circuit.
Here, we have series-parallel circuit. You notice we have our R1 and R2 are in series; and R3 and R4 are in parallel. What we are going to do is… this is our goal here, to simplify to a power supply and one resistor. Our goal is to simplify this circuit to a single power supply and a single resistor.
We know what our power supply and here we got 10 volts here, put a little ground right here. What we want to know is the combined resistance that we have over here. What we will do is we will add up these two together and we will see what 250 and 750. These two, we could combine in one single component of 1000.
We want to combine these into a single component as well so let's get our calculator and that will aid us in calculating the parallel value. We have 800 ohms, let's say we put in 800 and we do the one over function plus 500 and then again we will do the one over function and then equals and there 3.25 and then we will do the one over function. So the total resistance would be 307 ohms. We could ex out that and that put in one value here of 307 ohms. Our total resistance, where we could say 1307ohms that would be simplified values for that particular circuit. What we did is that we simplified this into a power supply and one resistance.
Here is another one. Let's go ahead and simplify it. We'll note that we have these two components are in series but these three are in parallel. Again, let's get our calculator and calculate the parallel resistance. Let's start with 400 ohms, we'll do the one over function; add that to 500 and the one over function, we'll add that finally to 2000 and the one over function. This will equal … five exponent minus three. We do the one over function here and the total resistance is by 200 ohms in the parallel portion of the circuit.
If we could eliminate this put of the circuit, we could replace it with a 200-ohm component. If we were to redraw this circuit, we have our 50 volts. We want to reduce this to a single component. We now have three components that in series. We have 200, 400 and 500 ohms. We have reduced this series-parallel circuit to a single power supply and one component.
This is also in this section. We don't have any component values here but we do want to talk about this and I have subtitled this ‘What is this?' We could look at this circuit and let's talk about it. Notice we have R1 and R2, these are in parallel. We could combine these R1 and R2. Those represent a series circuit and down here, R9 and R10. We could combine those two in R9,R10. We could do a parallel value here. When we get over here, things became a little more complicated and it isn't so clear as to what is in parallel or what is not.
We need to take a look at this. R3 and R7, they seem to be in series but then R6 is connected here in here in a funny way. R6 is not in series or it isn't parallel either. I think we could go over here. These two components are connected to the same … but we could put this two R4,R5 into a parallel relationship.
Let's jump to the next slide. I think we got another picture of this that has combined those two lower components, the two upper end, and then R4, R5. Since these two effectively once we do the parallel conversion here. They could summarize to something like this and they could do a series-parallel circuit and combine those components. That would make perfect sense.
Over here, we could combine R4 and R5 but still R6 is not in series and is not in parallel. We refer this as a complex circuit. It is neither series nor it is a parallel. We won't look at this in this particular course. If you take advanced course, we could go in and analyse a circuit such as this. Typically, this particular circuit is referred to as Wheatstone bridge but we will not be doing calculations for this. You do need to be able to identify what is a complex circuit, we deal with series, we will deal with parallel, we will deal a series-parallel. We will not deal or we will not do calculations for the complex circuits.
This is another short lesson. We looked at the series-parallel circuits and we played by simplifying them. When you go into you text, there's quite a good few examples addressing this. You will need to work through these because there are quite a few problems to be solved in this section so it went quite quickly as a presentation but I want you to get familiar with these kinds of calculations. There's one thing to see someone else do and not to do it yourself. Make sure that you are fluent in doing the kind of thing we did in a circuit, calculating series into series-parallel circuits and simplifying them into a single power supply and single resistor.