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Welcome back, this is Dr. 
Ferry. 

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This lesson will be on a lab demo, The 
Applications of Inductance. 

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So far in this module, we've talked about 
the theoretical aspects. 

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We've learned how to analyze circuits 
with capacitors, inductors. 

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And it's a nice way of ending out this 
module, is to look at some physical 

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applications of inductors and capacitors. 
We've already done a lab demo on 

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capacitors. 
So now this time, we'll be doing a lab 

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demo on the applications of inductors and 
inductance. 

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Now let's [INAUDIBLE] look at some 
applications of inductance. 

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An inductor is just basically a coil of 
wire. 

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Inductors are really common. 
And they're used in power generation, 

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inductive sensors, and in inductive 
actuators. 

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The basic mechanism to generate 
electricity is by moving a coil inside of 

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a magnetic field or by moving the 
magnetic field [INAUDIBLE] a coil. 

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A guitar pickup uses, the electric guitar 
pickup uses this sort of principle. 

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In that case, the electric guitar pickup 
has a permanent magnet, as shown here. 

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We've got a permanent magnet and a coil 
of wire wrapped around it. 

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And it generates a magnetic field because 
of that permanent magnet. 

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If I take I it in a conductor like a 
guitar, metal guitar string and I cross 

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through those lines, I'm going to 
generate current in this coil. 

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Now, let's take a look at a kind of a 
simple experiment to show a homemade 

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guitar pickup. 
This is a homemade guitar pickup. 

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It is just a bunch of wire coiled around, 
very fine gauge wire, coiled around a 

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permanent magnet. 
And it creates magnetic field about it. 

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And this is a metal guitar string. 
As I pluck it [SOUND] then it cuts those 

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magnetic lines and it creates a voltage. 
Now this line showing out here, this is 

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connected to oscilloscope. 
So the only electricity that's going on 

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here is the one that I'm generating. 
[SOUND]. 

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There's no external power supply here. 
If I look at the oscilloscope, as I pluck 

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this [SOUND] you can see the generated 
voltage. 

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[SOUND]. 
And that's how guitar pickups work. 

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They're just sensors made of this 
induction, inductive element. 

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Now this is a passive sensor, looking 
back at this experiment here. 

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This is a passive sensor. 
As I said, there's no external power 

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supply. 
Active sensors, which have their own 

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power supply, are often used in metal 
detectors and in inductive proximity 

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sensors. 
Going back to this drawing here, they act 

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as sensors, have a current flowing 
through this because of the power supply. 

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So they've got current flowing through 
this. 

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And that generates this electric field or 
magnetic field. 

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And, in fact, if you have a changing 
voltage or, changing current through 

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here, it's going to have a changing 
magnetic field. 

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When that comes in contact with a 
metallic object, it interacts with this 

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field, which then changes the current 
flow in the coil. 

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And there's a circuitry attached to that 
that detects that change in the current. 

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A very common inductive sensor that 
you'll see in applications is metal 

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detectors. 
Metal detectors of the kind of portable 

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type that you can find metal on beaches, 
but also metal detectors that are in 

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stores and events when you have to walk 
through the metal detector to get in. 

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It's just a magnetic field that you're 
walking through, and the metal disrupts 

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that magnetic field which then, again, 
disrupts the current generating that 

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magnetic field. 
A very common inductive sensor in 

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mechanical systems is a linear variable 
differential transformer, an LVDT. 

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That's that's a case where I've got a 
primary coil and in addition, I'm going 

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to have a secondary coil. 
And this is used to measure linear 

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displacement in mechanical applications. 
Now, inductive actuators, are ones that 

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drive mechanical devices. 
They rely on the principle of 

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electromagnet, which is again a coil with 
a current flowing through it. 

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If I just have just the basic coil with a 
current flowing through it, it generates 

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a magnetic field. 
The stronger the current, the stronger 

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the magnetic field. 
And that means I've created a magnet, an 

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electromagnet. 
[SOUND] This is an example of 

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electromagnet. 
I've got two leads here. 

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I hook up these leads to a power supply 
and inside here is a coil of, of wire. 

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And this, when they, current going 
through that coil gets large enough, the 

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magnetic field gets large enough, it 
becomes a magnet. 

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A solenoid is a electromagnet which has a 
core that goes into it. 

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And that core is pulled in when the 
electromagnet, magnetic field gets large 

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enough. 
So when the current gets large enough, 

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magnetic field gets strong enough, it 
pulls this in. 

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Now this right here is just a mechanical 
spring. 

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And it's used to provide a restoring 
force because when the current gets low 

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enough then the magnetic field drops, but 
I need a restoring force to push it back 

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out. 
So the magnetic, the magnetic field pulls 

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it in. 
The spring pushes it back out. 

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[SOUND] Let's see the operation of a 
magnetic, of a solenoid. 

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Solenoids are often times used as valves 
to open and close valves. 

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Now this is one that I've got hooked up 
to a power supply and I'm going to turn 

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this. 
Let me hold my finger on it to, because 

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it's going to move. 
I'm increasing the voltage this and, 

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thereby, increasing the current. 
[SOUND] And this one I got to about 14, 

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15 volts. 
It reached half an amp, which is quite a 

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bit. 
And the half an amp, it's large enough, a 

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strong enough magnetic field, that it 
pulled that shaft inward. 

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If I drop the current, the [INAUDIBLE] 
voltage and current through this, 

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[BLANK_AUDIO] at some point in time the, 
the spring force is large enough to pull 

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it back out. 
So that is a solenoid, oftentimes used 

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as, to open and close valves. 
[SOUND] Another example of an 

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electromagnet is in a loudspeaker. 
This is a cross-sectional area of a 

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loudspeaker. 
It's cut in half. 

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And this is a coil that's in there. 
So the coil is also cut in half. 

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You can see the inside of the coil. 
So the coil of wire is right there. 

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You can see it, a full one looking right 
there. 

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And there's a diaphragm or cone attached 
to the electromagnet. 

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And the electromagnet reverses polarity 
depending on how you, what the current is 

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like going through these coils, through 
the coil. 

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It reverses polarity, pushing against or 
pulling the diaphragm towards a 

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[INAUDIBLE] permanent magnet. 
So as you reverse the polarity of the 

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current going through that, that, coil, 
it's going to push or pull this speaker 

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inward and outward, this diaphragm. 
And, therefore, it creates the sound. 

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So that's a good application of of 
inductance. 

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So we've looked at inductance with 
respect to sensors, as well as actuators. 

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In summary, we discussed the energy 
exchange in inductors, from mechanical 

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energy to electrical, and from electrical 
to mechanical energy. 

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And that was done all through inductors. 
We also shared that moving a conductor in 

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a magnetic field induces current. 
And changing current in a coiled wire 

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causes a magnetic field. 
And we use these properties to be able to 

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build applications with inductance. 
We looked at passive sensing, such as, in 

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a guitar pickup. 
We looked at active sensing, such as 

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metal detector. 
And we also looked at actuation through 

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the, the usage of solenoids with 
speakers. 

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I like to remind people to go to the 
forum and ask questions as you need, 

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answer questions that other people, post. 
And you might want to start a new forum 

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topic that is applications of inductors 
and capacitors that you're familiar with. 

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Thank you and I'll see you online.