Welcome back, this is Dr. 
Ferry. 
This lesson will be on a lab demo, The 
Applications of Inductance. 
So far in this module, we've talked about 
the theoretical aspects. 
We've learned how to analyze circuits 
with capacitors, inductors. 
And it's a nice way of ending out this 
module, is to look at some physical 
applications of inductors and capacitors. 
We've already done a lab demo on 
capacitors. 
So now this time, we'll be doing a lab 
demo on the applications of inductors and 
inductance. 
Now let's [INAUDIBLE] look at some 
applications of inductance. 
An inductor is just basically a coil of 
wire. 
Inductors are really common. 
And they're used in power generation, 
inductive sensors, and in inductive 
actuators. 
The basic mechanism to generate 
electricity is by moving a coil inside of 
a magnetic field or by moving the 
magnetic field [INAUDIBLE] a coil. 
A guitar pickup uses, the electric guitar 
pickup uses this sort of principle. 
In that case, the electric guitar pickup 
has a permanent magnet, as shown here. 
We've got a permanent magnet and a coil 
of wire wrapped around it. 
And it generates a magnetic field because 
of that permanent magnet. 
If I take I it in a conductor like a 
guitar, metal guitar string and I cross 
through those lines, I'm going to 
generate current in this coil. 
Now, let's take a look at a kind of a 
simple experiment to show a homemade 
guitar pickup. 
This is a homemade guitar pickup. 
It is just a bunch of wire coiled around, 
very fine gauge wire, coiled around a 
permanent magnet. 
And it creates magnetic field about it. 
And this is a metal guitar string. 
As I pluck it [SOUND] then it cuts those 
magnetic lines and it creates a voltage. 
Now this line showing out here, this is 
connected to oscilloscope. 
So the only electricity that's going on 
here is the one that I'm generating. 
[SOUND]. 
There's no external power supply here. 
If I look at the oscilloscope, as I pluck 
this [SOUND] you can see the generated 
voltage. 
[SOUND]. 
And that's how guitar pickups work. 
They're just sensors made of this 
induction, inductive element. 
Now this is a passive sensor, looking 
back at this experiment here. 
This is a passive sensor. 
As I said, there's no external power 
supply. 
Active sensors, which have their own 
power supply, are often used in metal 
detectors and in inductive proximity 
sensors. 
Going back to this drawing here, they act 
as sensors, have a current flowing 
through this because of the power supply. 
So they've got current flowing through 
this. 
And that generates this electric field or 
magnetic field. 
And, in fact, if you have a changing 
voltage or, changing current through 
here, it's going to have a changing 
magnetic field. 
When that comes in contact with a 
metallic object, it interacts with this 
field, which then changes the current 
flow in the coil. 
And there's a circuitry attached to that 
that detects that change in the current. 
A very common inductive sensor that 
you'll see in applications is metal 
detectors. 
Metal detectors of the kind of portable 
type that you can find metal on beaches, 
but also metal detectors that are in 
stores and events when you have to walk 
through the metal detector to get in. 
It's just a magnetic field that you're 
walking through, and the metal disrupts 
that magnetic field which then, again, 
disrupts the current generating that 
magnetic field. 
A very common inductive sensor in 
mechanical systems is a linear variable 
differential transformer, an LVDT. 
That's that's a case where I've got a 
primary coil and in addition, I'm going 
to have a secondary coil. 
And this is used to measure linear 
displacement in mechanical applications. 
Now, inductive actuators, are ones that 
drive mechanical devices. 
They rely on the principle of 
electromagnet, which is again a coil with 
a current flowing through it. 
If I just have just the basic coil with a 
current flowing through it, it generates 
a magnetic field. 
The stronger the current, the stronger 
the magnetic field. 
And that means I've created a magnet, an 
electromagnet. 
[SOUND] This is an example of 
electromagnet. 
I've got two leads here. 
I hook up these leads to a power supply 
and inside here is a coil of, of wire. 
And this, when they, current going 
through that coil gets large enough, the 
magnetic field gets large enough, it 
becomes a magnet. 
A solenoid is a electromagnet which has a 
core that goes into it. 
And that core is pulled in when the 
electromagnet, magnetic field gets large 
enough. 
So when the current gets large enough, 
magnetic field gets strong enough, it 
pulls this in. 
Now this right here is just a mechanical 
spring. 
And it's used to provide a restoring 
force because when the current gets low 
enough then the magnetic field drops, but 
I need a restoring force to push it back 
out. 
So the magnetic, the magnetic field pulls 
it in. 
The spring pushes it back out. 
[SOUND] Let's see the operation of a 
magnetic, of a solenoid. 
Solenoids are often times used as valves 
to open and close valves. 
Now this is one that I've got hooked up 
to a power supply and I'm going to turn 
this. 
Let me hold my finger on it to, because 
it's going to move. 
I'm increasing the voltage this and, 
thereby, increasing the current. 
[SOUND] And this one I got to about 14, 
15 volts. 
It reached half an amp, which is quite a 
bit. 
And the half an amp, it's large enough, a 
strong enough magnetic field, that it 
pulled that shaft inward. 
If I drop the current, the [INAUDIBLE] 
voltage and current through this, 
[BLANK_AUDIO] at some point in time the, 
the spring force is large enough to pull 
it back out. 
So that is a solenoid, oftentimes used 
as, to open and close valves. 
[SOUND] Another example of an 
electromagnet is in a loudspeaker. 
This is a cross-sectional area of a 
loudspeaker. 
It's cut in half. 
And this is a coil that's in there. 
So the coil is also cut in half. 
You can see the inside of the coil. 
So the coil of wire is right there. 
You can see it, a full one looking right 
there. 
And there's a diaphragm or cone attached 
to the electromagnet. 
And the electromagnet reverses polarity 
depending on how you, what the current is 
like going through these coils, through 
the coil. 
It reverses polarity, pushing against or 
pulling the diaphragm towards a 
[INAUDIBLE] permanent magnet. 
So as you reverse the polarity of the 
current going through that, that, coil, 
it's going to push or pull this speaker 
inward and outward, this diaphragm. 
And, therefore, it creates the sound. 
So that's a good application of of 
inductance. 
So we've looked at inductance with 
respect to sensors, as well as actuators. 
In summary, we discussed the energy 
exchange in inductors, from mechanical 
energy to electrical, and from electrical 
to mechanical energy. 
And that was done all through inductors. 
We also shared that moving a conductor in 
a magnetic field induces current. 
And changing current in a coiled wire 
causes a magnetic field. 
And we use these properties to be able to 
build applications with inductance. 
We looked at passive sensing, such as, in 
a guitar pickup. 
We looked at active sensing, such as 
metal detector. 
And we also looked at actuation through 
the, the usage of solenoids with 
speakers. 
I like to remind people to go to the 
forum and ask questions as you need, 
answer questions that other people, post. 
And you might want to start a new forum 
topic that is applications of inductors 
and capacitors that you're familiar with. 
Thank you and I'll see you online.