 ## Physics

Learn the toughest concepts covered in Physics with step-by-step video tutorials and practice problems by world-class tutors

27. Resistors & DC Circuits

# Resistors and Ohm's Law

1
concept

## Resistance and Ohm's Law 3m
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Hey, guys. So in this video, we're going to cover two really important concepts, the resistance of a conductor. And that's really powerful equation that you need to know called OEMs law in order to solve problems. Let's go ahead and check it out. So before when we talked about the charges that flow through a conductor, we've sort of pretended that these electrons or charges could pass through this conductor sort of unobstructed. They were freely able to go from one side to the other. The reality is that they're not that simple, because inside of a conductor there are atoms. And as these electrons are traveling through this conductor, they're bouncing off of the atoms inside of that conductor. And all of those collisions that take place sort of create this internal friction that resists the amount of charges that could go from one side to the other. In other words, this internal friction resists the current. So if you have a conductor and you place some voltage or some potential difference across it, and you have these atoms that air trying to cross from one side to the other, the relationship between the current and the voltage is given by this equation where eyes equal to V. But you have to divide it by this term called Are now this our term is called the resistance and this resistance here is basically the ability for a conductor to resist the amount of charges that are trying to make it across in a certain amount of time. Three units for this resistance are in homes and given by this this letter, uh, this Greek letter capital Omega And what this resistance represents is that the larger the resistance of a conductor, the smaller amounts of current can pass through with smaller amount of charges can pass through in a specific amount of time. So we have this relationship between I, V and R, but more common than you'll see it written in this way. And this is called OEMs law. This is really important. You definitely need to commit this to memory. This is V equals I times are this is kind of like the f equals m A of physics too. So definitely commit V equals ir to memory because you're gonna be using it a lot in the future. Alright, guys, it's basically it. That's the equation that you need to know. Let's go ahead and work out some practice problems right here. Okay, so we've got a conductor and we have a voltage of 10 volts across it. We're told that six micro columns of charge flows through it every 1.5 seconds. Were supposed to figure out what the resistance of this conductor is. So as a variable when other. In other words, we're trying to figure out what our is. And we've only got one equation to you so far. So we're gonna use OEMs. Law V equals I times are, if we rearrange for this, we know that the voltage divided by the current is equal to the resistance. So we have with the voltage is that's just the 10 volts. So how do we figure what the current is because not told without explicitly is So we have to do is we have to say that the currents is going to be the charge divided by the amount of time. Remember, we can use this relationship that I is equal to Delta Q, divided by Delta T from a previous video. So if we have an amount of charge, that's flowing through six times. 10 to the minus six, divided by an amount of time, which is 1.5 seconds on. This is just gonna be four times 10 to the minus six. And that's gonna be amps. Remember that current is gonna be amps. Okay, so now we have to plug this basically back into this equation, and we have that. The resistance is equal to 10 volts, divided by the amps, which is four times 10 to the minus six. And we have a resistance that's going to be 2.5 times 10 to the sixth. And that's gonna be in homes. That's sort of like the simple for that. All right, so that's how you figure out the resistance of a conductor. Alright, guys, Thanks for watching. Let me know if you guys have any questions.
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concept

## Resistivity & Resistors in Circuits 5m
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Problem

A resistor has a current through it of 5 A. If the EMF across the resistor is 10 V, what is the resistance of this resistor?

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example

## Current Through Unknown Resistor 2m
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