Hey guys.
This here is a parallel plates capacitor and I will use this for some experiments today.
And these here are 12 experiments that I’ve made during my university time for the assignment
that is called electro magnetism.
I will put all the titles for each experiment on the screen so you can take a look.
I want to replicate some, or maybe all of these experiments on my channel and teach
you something new.
Some of these are very fun and very informative but unfortunelly, for some of them I need
really expensive gear that I don’t have.
Maybe I will be able to convince my university to let me record some videos inside their
laboratories.
Anyway, today we start with the first class and it will be about capacitors.
I want to show you how they work, some related equations with the capacitors, what types
we have and how could the area, the dielectric and the distance between the plate could affect
the capacitor characteristics.
Also, we will see how to measure the stored charge inside a capacitor using some cool
formulas.
So, let’s get started.
What’s up my friends, welcome back.
I’ve bought this kit from AliExpress and it should be good enough for some fun and
informative experiments.
These are two conductive metal plates, a fiberglass dielectric and two supports made out of plastic
so they are not conductive.
Like that we can make sure the charge will stay on the metal plates.
So, how dose a capacitor works?
Well, the most basic representation of a capacitor are two conductive plates like these ones,
placed together side by side, but never touching and usually we have some sort of dielectric
material in between, and we will see what a dielectric is in a moment.
On the other side we know that electrons have a negative charge.
Negative with negative will repel each other and positive with negative will attract, all
thanks to electric fields.
The idea of a capacitor is to store these electrons on its metal plates.
But you see, you can’t really add more electrons on a metal because they will get pushed out
by the other electrons.
Unless you apply some positive charge on the other side so they would get attracted.
This attraction could overcome the pushing force created of the electrons repelling each
other and in this way we would have a bigger charge stored on to the metal plates of the
capacitor.
To create negative and positive charge, we apply a voltage differential to the plates
but the plates are never touching each other.
With this voltage difference we can now push electrons on to the right plate and suck them
out from the left plate creating a positive charge.
Since the metal plates are not touching, the electrons can’t go to the other side to
fill the positive holes.
But there is an electric force between the positive and negative charge and this force
will keep them together.
So even if I disconnect the voltage supply, since the charge has no place where it could
go, the capacitor will keep its charge.
That’s basically how we can store energy inside of a capacitor.
As you can see here, I have a huge capacitor in series with an LED but the LED is off.
Now I supply 5 V and charge the capacitor up.
Even if I remove the supply, the LED is still on for a few seconds till all the chare stored
inside it is gone.
Basically, a capacitor is like a battery, but it charges and discharges a lot faster.
ANIAMTION.
But what if I connect the battery backwards.
For this ideal capacitor, the left and the right metal plates are the same so it would
work without problems.
But depending on the materials that we use to manufacture the capacitors, this might
be a problem and this could happen to your capacitor.
You see there are a few types of materials we could use to make capacitors such as ceramic,
tantalum, electrolytic, polymer, mica, film or silicon and they each have their own characteristics.
For example, for electrolytic and tantalum capacitors, these materials make them to be
polarized and we use symbols such as these ones to mark them as polarized or non polarized.
We can see the electrolytic or tantalum capacitor having a line indicating the negative pin.
If you place them backwards, they might not work or even explode.
Ok so that was the basic part about capacitors.
Till now between the metal plates we had air.
We call the material between the plates a dielectric, and in electromagnetism, this
is an electrical insulator that can be polarized by an electric field.
Air is a dielectric, plastic is another one, rubber could be a dielectric, glass could
also be or even wood could be a dielectric for capcacitors.
But depending on the used material for the dielectric, the capacitor properties would
change.
The unit to measure capacitors is capacitance and is measured in Farads in honor to Michael
Faraday.
This capacitance is ideally equal to the Area of the plates divided by the distance between
the plates and multiplied by an electrostatic constant.
This constant is equal to epsilon 0 multiplied by epsilon r where epsilon 0 is the permittivity
of the void and epsilon r is the permittivity of the used material.
So obviously, the capacitance of a capacitor is affected by the used material for the dielectric.
Here is a table with different materials and each respective permittivity.
As you can see, the air has a permittivity of 1.
But the glass for example has a permittivity between 5 and 10 so obviously, using the formula
before, if the distance and the Area stays the same but we change the dielectric from
air to glass, the capacitance should be higher.
Let’s test that.
Here I measure the capacitance of these two plates with air in between, and is around
180 picofarads.
Now I get this fiber glass palate.
This also has a plastic handle so is non-conductive.
I insert this plate between the plates and as you can see, the capacitance is not higher,
around 320 picofarads.
I now do the same with this glass plate I have from one of my 3D printers.
Once again, without changing the area or the distance, the capacitance is a bit higher.
Having a solid material between the conductive plates would make sure the conductors would
never touch and also reduce arcing between the plates.
The better is the insulator, the voltage should be higher in order to arc.
From the same formula, we can also see that the capacitance could change according to
the distance.
The smaller is the distance between the plates, the higher would the capacitance get.
Again, I measure the capacitance of these two metal plates.
I now decrease the distance in between.
As you can see, the capacitance is now higher.
And it would get lower if I increase the distance.
To get very high values, manufacturers are using very thin materials wrapped together
so the conductive material would always be insulated.
Like this we have a huge area and very small distance in between resulting into high capacitance
values.
And that’s the third experiment we should make.
The Area is also important since it is also part of the formula before.
The bigger is the shared area, the higher would the capacitance get.
In this example, as I slide one plate to the side, the common area is getting smaller so
the capacitance is getting lower as you can see.
Actually, we can see this with variable capacitors such as this one here.
By rotating the knob, more or less area is shared so the value is getting higher or lower.
And as I’ve told you before, to get the highest area and minimum volume, manufacturers
pack the capacitors like this where the conductor and the dielectric are wrapped together in
a cylinder.
Another formula is this one where the electric field is equal to the applied voltage divided
by the distance.
The electric field must be constant so what happens if I increase the distance with the
same voltage.
Well, another experiment we can do with these plates is to calculate the stored charge inside
the capacitor.
What we have to do is to charge the plates to let’s say 12V when the distance is 1mm
and then disconnect the power supply.
Then we increase the distance while measuring the voltage and distance, and according to
this formula before, since the field should be constant, the voltage must increase.
And that’s right, look, as the distance is getting higher the voltage is getting higher
as well.
We can make measurements and make a table like this one where we have the voltage and
the distance in mm.
Then we pass these values to inverted values, so 1 divided by the voltage and 1 divided
by the distance.
We graph these values like this.
Then we make the lineal regression of this line in excel.
That will give an equation such as this one.
This equation is actually representing this.
Now we get this number here and we call it A, for example.
Then from these two other formulas and the equation before, we can get that the Q, which
is the stored charge, is equal to epsilon 0 multiplied by the area of the capacitor
divided by that A number.
Since my capacitor is round, the area in my case is pi R squared where R is the radius
of my metal plate and we can easily measure that.
Place that area into our equation and we get the stored charge.
See the full step by step calculations on Electronoobs.com.
Instead of just 1 measurement, we can make 3 or 4 and make 4 different graphs.
Then we can make the mean between the values and get a more accurate result.
I have another example for you.
Let’s say you have this circuit with a capacitor in series with a resistor and we charge it
using a power supply.
Since it has a resistor, it will take some time to charge up and it will create a curve
like this.
I do that on my oscilloscope.
The time it takes to charge up to 63% is more or less equal to the resistance multiplied
by the capacitance.
So if we charge up the capacitor at 12V, 63% would be around 7.6V. I measure on the oscilloscope
the time it took to charge up to that voltage, and in my case I get 49ms.
If we divide that time by the used resistor, which in my case is 10.000 ohms, we get the
value of the capacitor of 4.9uF which is pretty close to the real value.
That’s how my capacitor meter made with arduino works.
You have that video below in the description if you want to see more.
All these examples were for DC voltage.
With AC the capacitor behaves differently.
The impedance of the capacitor under AC signals is like this where F is the frequency of the
AC signal.
So, since the F is under, the higher is the frequency the lower would the impedance of
the capacitor get.
That’s why we can make a low pass filter like this.
As the frequency is getting higher, the impedance of the capacitor is getting lower and lower
conducting more and more current towards ground.
So only lower frequencies could pass, the high frequencies are filtered.
The same would happen with high pass filter but the capacitor is now placed above like
this.
Some more information about capacitors is that also depending on the used materials
and technology, they have maximum voltage and usually is marked on their label.
If you apply more than that, again, this will happen.
Ideally, the capacitor could charge almost instantly but never exactly instantly because
that would mean there would be an infinite value of current in that exact moment.
There is always a small delay between zero and fully charged.
So you should know that the current passing through a capacitor is equal to its capacitance
multiplied by the voltage change divided by the time interval.
You have all these formulas and more on Electronoobs.com and the links are in the description.
I hope that you now know more about capacitors.
If so, consider giving me a like or comment below.
Stay tuned for more electromagnetism experiments and lessons on a future episode.
Thanks again and see you later guys.