Electrical Engineering: Ch 7: Inductors (1 of 20) What is an Inductor?

welcome to electron line in this chapter chapter seven we're going to talk about inductors now inductors actually very simple devices although there are a lot of different uses for inductors and a lot of different properties about electricity and magnetism that involve inductors so what is an inductor well in very simple terms an inductor simply is a wire wrapped around the tube that's all it is a wire wrapped around the tube so what's so special then about an inductor well it turns out that it has a very special property an inductor opposes a changing current but other words if there's DC current steady state current inductor does absolutely nothing it just sits there and there's no effect on the circuit whatsoever the moment the current tries to change that's when an inductor well basically jumps into action and tries to pose that change if the current tries to increase the inductor tries to keep it from increasing if the current tries to decrease the inductor tries to keep it from decreasing and that's why inductors are so useful in electrical circuits because of that specific property now physically an inductor here's a drawing of an inductor simply as a tube that tube could be simply a hollow tube with air inside then it's an air core inductor as we call it or it could have a metal or can have some sort of inductor inside but typically they like to use metal to enhance the magnetic field through the tube and we'll talk about that later but simply a wire wrapped around the tube the tube has a cross-sectional area it has a length and also an inductor has the number of turns as we call it each loop of wire around the tube is called a turn it's simply a loop also what you need to know about inductors is the number of turns per length in other words if this is a five centimeter inductor and there's a hundred turns that means there's a hundred turns per five centimeters or twenty turns per centimeter or two thousand terms per meter however you want to express it also when we talk about inductors we talk about what we call per me ability as who will see later there's always a magnetic field around the wire that cares a current and therefore as we loop a wire around the inductor will be a magnetic field inside the tube or inside the core and the permeability is the amount of magnetic field or I should say the permeability is the ability of the magnetic field to exist inside the tube relative to what's there if it's simply air then we use this permeability which has the units of 4pi times 10 to the minus 7 Weber's per amp times meters or Tesla's times meters per amp depending upon what units you want to use the permeability becomes larger as you put for example metal in there because metal can basically allow more magnetic field exist inside the tube versus air and so we'll show you the difference about that later as well the key idea with an inductor this is the electrical symbol for inductors it looks like a little wire inside a light bulb the old incandescent light bulbs that is and you can see that if the current is constant either if the current is 0 or the current is not zero but constant doesn't change the voltage across an inductor will be equal to zero however if the current is increasing in this direction the current is flowing in this direction the current is increasing the voltage across the inductor will be some value and it'll be negative on this side and positive on this side but other words it will set up a potential difference across inductor that tries to apposed increase it tries to drive a current in the opposite direction if the current is decreasing then the voltage across the inductor will be like this positive in this side negative on this side because it will set up a current in the same direction as the decreasing current trying to keep it from decreasing so that's how we look at inductors there's only potential difference across an inductor if the current is actually changing here's the equation that defines how much the voltage is across an inductor it's equal to the inductance L the inductance of the inductor times the rate of changes of turn through the inductor now what do we mean by inductance well let's go over here for a moment take a look at this a resistor has resistance and we use the letter R to indicate resistance it opposes our current a DC current AC current doesn't matter it simply opposes a current according to Ohm's law a capacitor has capacitance it has the capacity to load up charges charges to store charges an inductor has inductance and we use a letter alfrid app and the units for inductance is Henry's now again one is inductance inductance is the ability to oppose the change in the current the large inductance the more it can oppose the change in the current the smaller inductance the less ability it has to oppose the change in the current and the inductance can be found by you and I didn't write the equation down so let me write the equation L is equal to the number turns in the inductor times the number turns per unit length in the inductor times the permeability of the inductor that would be the permeability of the chord inductor times the cross-sectional area so what we could do is you can write this in two different ways we could also write this as L is equal to N squared times mu times a divided by the length of the inductor and that is typically the way you see it in most textbooks but it could also be written as follows you can also say that the inductor is equal to the number loops times the number of loops per unit length times mu times a so you can also write it like this again where the small end simply means the number loops per unit length but this is typically the way you see it in most textbooks in other words you can actually calculate the value of the inductance of an inductor if you know how many loops there are let's say the 100 loops or a thousand loops you need to know the permeability it'll be this if it's air it'll be a larger number if it's a metal core the cross-sectional area so the physical size of inductor is important and the length of the inductor is important as well this will give you the the size of the inductance then you use that number in here multiply times the rate of change the current with respect to time and that will give you the voltage across the inductor remember inductors typically only have voltage across them not just typically but always always have voltage across them if there's a change in current and the voltage will be zero if there's no change in current now of course one more thing perhaps in essence that we'll talk about that later since the inductors made out of wire and since all wires have a small amount of resistance in essence all inductors have a small amount of resistance as well but we'll talk about that later I just didn't want to forget that so that you realize that there'll be a little bit of a voltage across inductor any inductor because they're made out of wire and wire still have a small amount of resistance but if we ignore that for now you can think of it like this now you know what in the ducktor is and we'll do a lot of videos on inductors to show you how we use them how we add them subtract them how to use them in circuits and so forth and that's what inductors

Channel: Michel van Biezen

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Keywords: ilectureonline, ilectureonline.com, Mike, Mike van Biezen, van Biezen, ilecture, ilecture online, Electrical Engineering, Output, Input, Current, Voltage, Voltage Sources, Chapter 7, Ch 7, Inductors, What is an Inductors?, Permeability, Oppose a change, Wires Wrapped Around a Tube, Resistors, Capacitor

Id: z-C-tu-80jA

Length: 7min 48sec (468 seconds)

Published: Mon Jun 27 2016