Objectives
Differentiate parallel and series circuits
Calculate the voltage, intensity and resistance of circuits
Use Ohm’s law to find a relationship between tension, intensity and resistance
Introduction
In this lesson, we will be talking about some very important calculations involving electrical circuits that will, without a doubt, help you when learning about electrical circuits.
To start, I would like to just say that this lesson requires some previous knowledge on the nature of electric circuits and the meaning of voltage, intensity and resistance.
Parallel and series circuits
Electrical circuits come in two types: parallel and series circuits. Knowing the difference between the two is extremely important for this lesson and so I am taking the time to teach you, or possibly remind you, about them. In short, all the components of a series circuit (for example, light bulbs) are found on a singular wire whereas parallel circuits have multiples paths for different components. For some examples, see this lesson’s video.
The characteristics between the different kinds of circuits present us with a very interesting property. Let’s say we have a series circuit that has three light bulbs. If I were to remove any of the three lightbulbs, the circuit would then be open and all the light bulbs would turn off. If these light bulbs were in a parallel circuit, however, the removal of any of the light bulbs would have no effect on the others because each of them has their own path connecting them to the power source.
Total voltage, intensity and resistance
Every circuit has its own total voltage, intensity and resistance. By “total”, I mean the value that you get when you put together either the voltage, intensity or resistance of all the parts of a circuit. To calculate these “total” values, we use very important formulas, but be wary! These formulas are different for series and parallel circuits. Let’s look at these formulas for series circuits first:
For voltage, we have:
VT=V1+V2 ... +Vn
In simpler terms, the total voltage of a series circuit is the sum of the voltage at all of the circuit components.
For intensity, we have:
IT=I1=I2 ... =In
In simpler terms, the total intensity of a series circuit is the same as the intensity at all points of the circuit.
For resistance, we have:
RT=R1+R2 ... +Rn
In simpler terms, the total resistance of a series circuit is the sum of the resistance of all of the circuit components.
Again, for parallel circuits, these formulas are different:
For voltage, we have:
VT=V1=V2 ... =Vn
In other terms, the total voltage of a parallel circuit is the same as the voltage at all points of the circuit.
For intensity, we have:
IT=I1+I2 ... +In
In other terms, the total intensity of a parallel circuit is the sum of the intensities of each of the circuit paths.
For resistance, we have:
RT=(R1^-1+R2^-1 ... + Rn^-1)^-1
This formula looks complicated when you first look at it, but it does make sense. Let’s take some time to explain it. When I add a new path to a parallel circuit, even though it has resistance, I’ve still given the charge a new path to go along which actually makes it faster. A good analogy for this is a highway where the road is the circuit and the cars are the charge. Say I add a new lane to my highway that is quite thin. That means that not too many cars will be able to easily use that lane but that overall, the traffic of the highway will go down because there is a new lane. This formula takes this phenomenon into effect by inverting the resistance values (putting them to the power of -1).
In all:
Ohm's law
Born in 1789, Georg Ohm, a Bavarian scientist, set an amazing law that really comes into handy for problems involving electrical circuits. His law, Ohm’s law, states that voltage in volts equals intensity in amperes times resistance in ohms. By moving the terms of this law around, we also see that:
These formulas are used very often in evaluations to solve problems involving both parallel and series circuits. See this lesson’s video for some examples.
Conclusion
I hope you have enjoyed learning about these awesome formulas. I would like to take the time, again, to remind you that what we have talked about today will definitely come in handy if you study electrical circuits more in depth. Thank you for taking the time to read this electrifying lesson!
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