Capacitors
Just a little math, :-\
6.241 × 10^18 electrons
That is a lot of electrons. We call that a Coulomb of electrons.
Pronounced Cool Ohm, like an ohm who smoked a joint. 8)
If you pass one of these cool ohms thru a wire in one second, you have an Ampere.
But the first capacitor probably held a lot less charge than a cool ohm, because it was simply a glass of water with a coat hanger stuck into it, with some crazy guy named Ewald Georg von Kleist, who back in 1745, thought it would be cool to mix water and electricity. (what an idiot ) ;D,
von Kleist charged up the water, via the coat hanger and electrical generator.
His right hand was wrapped around the jar, his left hand had the generator ground, and he probably had a friend plug in the generator which was connected to the coat hanger, which was submersed in the jar.
So the glass jar was the insulator, his right hand was one plate of the capacitor, and the water was the other plate.So you disconnect the generator , and reach over with your left hand and touch the coat hanger, and Zap!
Cardiac arrest. No, jus kidin, but he felt a mild shock.
Little did von Kleist know that some Dutch guy had a similar but improved version of the von Kleist jar going on at the same time.
Pieter van Musschenbroek of Leiden (Leyden) had foil wrapped around the jar instead of his hand.
A lot smarter idea in my opinion.
So foil on the inside of the jar, foil on the outside, the glass jar as insulator, and Viola!, insta capacitor.
Now if you keep increasing the voltage while you are charging up the jar, more cool ohms of electrons, or charge, will flow onto the plates.
So for the same size plates, the more voltage you apply, the more cool ohms you will store.
So we have voltage, and we have electrons, therefore, we have kind of battery.
Now the smaller the plates for the same amount of charge means the higher the voltage between those plates.
This is because you have electrons stacked up on each other which creates a stronger space charge.
There is a relationship then, between the Capacitor and the charge and voltage.
We can define this relationship with a little more math, :-[ as
Capacitance = q/V
where q is charge in cool ohms, and V is the voltage between the plates.
The SI unit of capacitance is the farad; 1 farad is 1 coulomb per volt.
We mostly use a much smaller value than the Farad, called the micro farad, unless you are pimpin out your ride with a sub woffer. ;D
Notice that 1 cool ohm divided by 1 volt equals 1000 cool ohms divided by 1000 volts,
and both equal 1 Farad.
so Capacitance is just a ratio. Not an energy measurement.
It is a ratio between how much charge on the plates is going to equal how much voltage between those plates.
Or, you could read it the other way and say that Capacitance is how much voltage will be needed on the plates to store a certain amount of charge.
The higher the Capacitance, the less voltage will be needed on the plates to needed to store the same amount of charge.
This voltage=charge aspect of the capacitor brings rise to a saying that describes the capacitor, we say that
A capacitor has the ability to resist a change in voltage.
In other words, if you jack up the voltage on a cap, it will absorb the electrons and thus keep the voltage down on the line until it can not store any more.
The time it takes for a cap to absorb charge and raise the voltage to a value of about 70.7 percent of the total voltage applied is called 1 time constant.
The time it then takes to rise up another 70.7 percent chunk of the remaining voltage differential is called 2 time constants.
If you add a resistor in series with the cap, it will slow down the charging rate.
The RC time constant then becomes simply, R times C, R in ohms, C in Farads.
Example: 1 ohm times 1 Farad = 1 Second
Now this ratio can be changed for a capacitor having a fixed plate area.
You can move the plates closer and the capacitance ratio goes up.
So for the same voltage, you will store more charge for the same plate area.
This relationship reads like this>
C=A/d
where A is plate area and d is the distance between the plates.
There is one last trick to these capacitors, the area between the plates.
It turns out that if you stick something other than air between the plates, the capacitance goes up.
This something is called the Dielectric.
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced toward the field and negative charges shift in the opposite direction. This creates an internal electric field which reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axis aligns to the field.
In other words, a capacitor will work better if the stuff in between the plates have some mojo going on as far as increasing the electric field between the plates. You can equate this dielectric with the different core materials you find in a transformer, different materials for different applications.
A dielectric has something called a dielectric constant, which is the factor by which it increases capacitance when used between the plates. Transformer lams have a similar number attached to them, permeability.
You have heard of electrolytic capacitors, right?
An electrolytic capacitor works well in that a slight voltage will store a bunch of electrons, making it useful in a power supply since it can absorb more charge per volt than a small radio frequency capacitor.
"Lytics" as they are sometimes called, use a conductive liquid in between the plates, thus requiring special construction to prevent a short circuit.
This liquid, or electrolyte, greatly increases the Capacitance of the cap.
Here is how they are built>
Aluminum electrolytic capacitors are constructed from two conducting aluminum foils, one of which is coated with an insulating oxide layer, and a paper spacer soaked in electrolyte. The foil insulated by the oxide layer is the anode while the liquid electrolyte and the second foil acts as the cathode. This stack is then rolled up, fitted with pin connectors and placed in a cylindrical aluminum casing. The two most popular geometries are axial leads coming from the center of each circular face of the cylinder, or two radial leads or lugs on one of the circular faces.
So electrolytic caps work great, but unlike all of the other types of caps, you have to observe correct polarity.
Reverse polarity will cause the cap to explode in some cases, so be careful!
