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# Introduction to Induction

Patrick Ford
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Hey guys. So for the next couple videos we're gonna be talking about a phenomenon called electromagnetic induction. And we're just gonna start off things by talking about where what it is and where it comes from. Let's check it out. So when we saw from the last couple of videos that when you have a coil or a loop of wire and you attach some voltage source across it, it has a current and we can determine the direction of that current. Using our right hand rule. Well that voltage source doesn't always have to be a battery. This voltage can actually just be created just by changing some things. And the word we're gonna be using for that is called induced. So the idea is that there are actually a couple of common ways to induce a voltage which induces a current in a coil of wire. Now, when scientists found this stuff, you know, hundreds of years ago, they actually found three common scenarios that would always induce occurrence. Let's check those out. Now, the first one is probably the most common one that you'll see. You might see it in a lab or something like that is when you have a bar magnet and you're basically moving this thing into and out of that coil, the idea is that you take a bar magnet and you're gonna move it in and out of the coil of wire. Now what scientists found is that when you move the bar magnet it would actually create a currents here inside of the coil that you could read on an instrument. So in other words you're creating some kind of induced current. So I'm gonna use I. I. N. D. For that. So basically you're creating some kind of induced voltage across this wire. Now the most important thing is that the bar magnet has to be moving. So when the bar magnet was moving there was an induced currents when it was stationary and V equals zero, there was no induced current. Let's take a look at the second example. Now the second example involves varying occurrence in an electro magnet. So when you have an electromagnet which is basically just a coil or a solenoid of like something like this and you attach it to some voltage source which can vary some of the words, this is v. What happens is that creates a current that's in the solenoid. So, alright, I solenoid and the idea is that as you vary this current, we know a current in a loop of wire creates a magnetic field. So basically just create something like this. And what happens is this current right here as you varied it as you want up and down would create an induced current like this. So I I. N. D. Now what what they found is that when the current was varying there was an induced current in the coil of wire. But when this current here in the solar was kept constant, there was nothing, there was nothing they could read in the coil. Now this last situation here involves the same exact electro magnet except now we attach a switch to it. So the idea is that as we basically turn the solenoid on and off. So, right, we're affecting the voltage right here. Now this i solenoid right here, that goes in this direction as we very, very rapidly turn this thing on and off, it would create an induced current in some direction. Over here in the coil of wire. Now, what they found is that when you turn this thing off very, very quickly there was some induced currents. So in other words, there was some I. I. N. D. But when you just kept it on or kept it off, whatever it was, there would be no induced currents now. So that's basically the three scenarios that that scientists most likely saw. So there's actually some in common about all three of these situations. Now, if you take a look in all three of these situations, what's really changing is actually the magnetic field. So, let's take a look at this first example where you had a bar magnet, we know a bar magnet has electric field lines that basically form loops like this and they form big, big loops like this. Right? So you have this magnetic field and these magnetic field forms loops. And what happens is as you are moving this bar magnet into and out of the coil, the magnetic field that's going through the coil is changing. Right? So we have some kind of be field that's changing in the second case here, we know that an elector of magnet basically behaves like a bar magnet. Because if you take your fingers and you coil and you curl your fingers in the direction of that uh in the direction of those loops, you have a magnetic field that points straight. Some other words, you have a magnetic field that points off in this direction. So you get the same exact current loops right here. And as you are ramping up the current inside of this electro magnet, it's basically making this be field stronger. We know that the relationship between i is that it's proportional to the b field of a solenoid. So the stronger the current, the stronger the magnetic field and the same principle happens over here as you're turning the electro magnet on and off, you're basically creating and destroying that magnetic field. So as you very, very rapidly change this thing as you very rapidly turn the switch on and off you're creating and then destroying this magnetic field just by turning that switch. Right, so we have this Byfield here. So in all three of these situations, the same thing happens, the magnetic field changes. And so because this is an interaction between magnet magnetism and electricity, this phenomenon is known as electromagnetic induction that we're gonna be talking about for the next couple videos. Now, the most important thing that you really, really need to know from this video is that the magnitude of the induced current through the coil actually depends on how fast all of these changes happen. So in the case where you had this bar magnet that was moving into and out of the coil, the idea was that the faster you move this coil in and out, the larger the induced currents. So if you went very very, very slow, the induced current would be very, very low. You went very very fast. The induced current would be very high. And when you have a current changing in the soul in order the electro magnet, the faster the current would change whether it was basically going up or down or you were turning the switch on and off, the larger the induced current was. Alright, that's what you need to know. There's no problems with this is mostly just conceptual. You really need to know this. So let me know if you guys have any questions, we'll move on to the next one.

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