Ohm’s Law - How Voltage, Current, and Resistance Relate | Ohm's Law | Electronics Textbook
Did you know that electrical current is affected by the voltage and resistance in a circuit? In this lesson, we'll use Ohm's law, which tells us how current, voltage, and resistance are related, as we work through several electric circuit examples. This equation, i = v/r, tells us. How electrical charge relates to voltage, current, and resistance. quick way to reference the relationship between voltage, current, resistance, and power. The three basic principles for this tutorial can be explained using electrons, or more. (amps), A. R is the resistance in ohms, Ω. The equation can be rearranged to find the resistance: R = V ÷ I. Question. 3 A flows through a V lamp. What is the.
So there's a couple of ways I can convince you that I1 equals I2, I3. One is I could just say if you experimentally tried it out using an ammeter, which measures current, you would see that they are identical. But the other way to think about it, and this time I'm going to actually talk about the electrons, so let's talk about things going in this direction, is-- so these electrons, through this wire, they can go as fast as they want to go, right?
The speed of light or close to the speed of light since they have very, very, very low mass. And we'll go into relativity one day. But once they get to this resistor, they start bumping into things, and they slow down. This resistor is a bit of a bottleneck, right? So as fast as they're traveling here, they have to slow down here. And if they slow down here, they have to slow down here, because if they kept going superfast here and then they slowed down here, then they would start building up here, and that just doesn't make sense, because we know that they're evenly spread out, et cetera.
And similarly, they might exit this resistor at a certain speed and then slow down even further as they bump into resistors here, but if they're going even slower at this point, then there would be a bottleneck here, so essentially, they would have to go at that rate throughout the whole thing.
And another way to think about it is the resistance is kind of a probabilistic thing. I know when you think on a macro level, you say, oh, it has this resistance. It just slows it down. But the longer there's a resistor, it increases the probability that some of the electrons are going to bump into something and create a little bit of heat, et cetera, et cetera.
So when you put resistors in series, what you're actually doing is increasing the probability that more electrons will bump into more things, right? Say there's an electron that travels-- say, somehow through freak luck, it doesn't bump into anything as it goes through here's because it's going really fast, but then it bumps into something here, right? It only increases the probability that something bumps into it.
So there's a bunch of ways you can think about it, and I encourage you to let me know if there's other ways that help you. But the current through this entire series circuit is constant.
Now if we say that, what else can we say? Well, if the current here-- let's say the current through here is I1. If the current through here is I1, what is going to be the voltage if I measured it from here to here? What is this voltage here? I measured it with a voltmeter. Well, V1 is going to be equal to I1 times R1. I don't know why I put an R. That's a 1, not an I.
Resistors in series (video) | Circuits | Khan Academy
I1 times R1, right? And similarly, if I measured the voltage from here to here, that voltage is going to be equal to I2 times R2. Let's say this is where I3 is. So the voltage, if I were to measure it from here to here-- But anyway, if we look at the voltage from here to here, it's going to be I3 times R3. So what we see is that the voltage across the entire circuit, which I can write as V-total, is going to be equal to the potential drops, the total potential drop across each of these devices.
So the way to think about it is that-- well, let's think about the electrons.
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The electrons here, they really want to get here. But after they've bumped around a little bit and they get here, they've experienced some potential drop. So the electrons here actually are a little bit less eager to get here.
And then once they've gone through here, maybe they're just tired of bumping around so much. And once they're here, they're a little bit less eager to get here.
So there's a voltage drop across each device, right? When we speak of a certain amount of voltage being present in a circuit, we are referring to the measurement of how much potential energy exists to move electrons from one particular point in that circuit to another particular point. Free electrons tend to move through conductors with some degree of friction, or opposition to motion.
This opposition to motion is more properly called resistance.
Introduction to circuits and Ohm's law (video) | Khan Academy
The amount of current in a circuit depends on the amount of voltage available to motivate the electrons, and also the amount of resistance in the circuit to oppose electron flow.
Just like voltage, resistance is a quantity relative between two points. Volt, Amp, and Ohm To be able to make meaningful statements about these quantities in circuits, we need to be able to describe their quantities in the same way that we might quantify mass, temperature, volume, length, or any other kind of physical quantity. Here are the standard units of measurement for electrical current, voltage, and resistance: Standardized letters like these are common in the disciplines of physics and engineering, and are internationally recognized.
Each unit of measurement is named after a famous experimenter in electricity: The amp after the Frenchman Andre M. The mathematical symbol for each quantity is meaningful as well.
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.
Resistors in series
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. At first, I'm gonna not make the path available to the electrons, I'm gonna have an open circuit here. I'm gonna make this path for the electrons. And so as long as our circuit is open like this, this is actually analogous to the closed pipe.
The electrons, there is no way for them to get to the positive terminal.
But if we were to close the circuit right over here, if we were to close it, then all of a sudden, the electrons could begin to flow through this circuit in an analogous way to the way that the water would flow down this pipe. Now when you see a schematic diagram like this, when you just see these lines, those usually denote something that has no resistance.
But that's very theoretical. In practice, even a very simple wire that's a good conductor would have some resistance. And the way that we denote resistance is with a jagged line.
And so let me draw resistance here. So that is how we denote it in a circuit diagram. Now let's say the resistance here is eight ohms. So my question to you is, given the voltage and given the resistance, what will be the current through this circuit?
What is the rate at which charge will flow past a point in this circuit?