Electrical/Electronic - Series Circuits
In a resistive DC circuit, both current and voltage are fixed, steady values. In an AC A simple diagram shows the relationship between all three values. Current . Shortcut to Series & Parallel Circuits, Kirchhoff's Laws, Current Division, Voltage Division Ohm's Law In DC circuits, the relationship between the current, voltage, . Georg Simon Ohm aka Georg Ohm is a German physicist found a proportional relationship between Voltage drop, Resistance and Current.
But intuitively, what is voltage? And what is resistance?
Ohm’s Law - How Voltage, Current, and Resistance Relate
And what are the units for them so that we can make sense of this? So to get an intuition for what these things are and how they relate, let's build a metaphor using the flow of water, which isn't a perfect metaphor, but it helps me at least understand the relationship between voltage, current, and resistance. So let's say I have this vertical pipe of water, it's closed at the bottom right now, and it's all full of water.
There's water above here as well. So the water in the pipe, so let's say the water right over here, it's gonna have some potential energy. And this potential energy, as we will see, it is analogous to voltage.
Voltage is electric potential, electric potential. Now it isn't straight up potential energy, it's actually potential energy per unit charge.
So let me write that. Potential energy per unit, unit charge. You could think of it as joules, which is potential energy, or units of energy per coulomb. That is our unit charge.What is voltage? -- What is current? -- What is resistance?
And the units for voltage in general is volts. Now, let's think about what would happen if we now open the bottom of this pipe. So we open this up.
Ohm’s Law - How Voltage, Current, and Resistance Relate | Ohm's Law | Electronics Textbook
Well, the water's immediately gonna drop straight down. That potential energy is gonna be converted to kinetic energy. And you could look at a certain part of the pipe right over here, right over here.
And you could say, well, how much water is flowing per unit time?
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And that amount of water that is flowing through the pipe at that point in a specific amount of time, that is analogous to current.
Current is the amount of charge, so we could say charge per unit time. Q for charge, and t for time. And intuitively you could say, how much, how much charge flowing, flowing past a point in a circuit, a point in circuit in a, let's say, unit of time, we could think of it as a second.
And so you could also think about it as coulombs per second, charge per unit time. And the idea of resistance is something could just keep that charge from flowing at an arbitrarily high rate. And if we want to go back to our water metaphor, what we could do is, we could introduce something that would impede the water, and that could be a narrowing of the pipe. And that narrowing of the pipe would be analogous to resistance.
So in this situation, once again, I have my vertical water pipe, I have opened it up, and you still would have that potential energy, which is analogous to voltage, and it would be converted to kinetic energy, and you would have a flow of water through that pipe, but now at every point in this pipe, the amount of water that's flowing past at a given moment of time is gonna be lower, because you have literally this bottleneck right over here.
So this narrowing is analogous to resistance. How much charge flow impeded, impeded. And the unit here is the ohm, is the ohm, which is denoted with the Greek letter omega. So now that we've defined these things and we have our metaphor, let's actually look at an electric circuit. So first, let me construct a battery.
So this is my battery. And the convention is my negative terminal is the shorter line here.
So I could say that's the negative terminal, that is the positive terminal. Associated with that battery, I could have some voltage.
And just to make this tangible, let's say the voltage is equal to 16 volts across this battery. And so one way to think about it is the potential energy per unit charge, let's say we have electrons here at the negative terminal, the potential energy per coulomb here is 16 volts.
These electrons, if they have a path, would go to the positive terminal. And so we can provide a path.
Let me draw it like this. The mathematical symbol for each quantity is meaningful as well. Most direct-current DC measurements, however, being stable over time, will be symbolized with capital letters.
Coulomb and Electric Charge One foundational unit of electrical measurement, often taught in the beginnings of electronics courses but used infrequently afterwards, is the unit of the coulomb, which is a measure of electric charge proportional to the number of electrons in an imbalanced state.
One coulomb of charge is equal to 6,,, electrons. Cast in these terms, current is the rate of electric charge motion through a conductor. As stated before, voltage is the measure of potential energy per unit charge available to motivate electrons from one point to another. Defined in these scientific terms, 1 volt is equal to 1 joule of electric potential energy per divided by 1 coulomb of charge.
Thus, a 9 volt battery releases 9 joules of energy for every coulomb of electrons moved through a circuit. These units and symbols for electrical quantities will become very important to know as we begin to explore the relationships between them in circuits. Ohm expressed his discovery in the form of a simple equation, describing how voltage, current, and resistance interrelate: In this algebraic expression, voltage E is equal to current I multiplied by resistance R.
Using algebra techniques, we can manipulate this equation into two variations, solving for I and for R, respectively: In the above circuit, there is only one source of voltage the battery, on the left and only one source of resistance to current the lamp, on the right.
In this first example, we will calculate the amount of current I in a circuit, given values of voltage E and resistance R: What is the amount of current I in this circuit? In this second example, we will calculate the amount of resistance R in a circuit, given values of voltage E and current I: