# Physics Review: E&M Capacitors and Capacitance #1 What Is A Capacitor

## Метаданные

- **Канал:** Michel van Biezen
- **YouTube:** https://www.youtube.com/watch?v=AsfkTTOdNMY
- **Источник:** https://ekstraktznaniy.ru/video/41988

## Транскрипт

### Segment 1 (00:00 - 05:00) []

Welcome to our elector online continuing our review of physics especially in the enm range of physics we're now going to talk about capacitors and capacity or capacitance um what is a capacitor well capacitor is a device that's essentially two metal plates close that are parallel to one another and that are placed very close together so that the distance between them is very small so that's and each of the plates has a certain cross-sectional area now typically if you want to turn that into a useful device what they do is they put some insulating material in between a dialectric material and then they roll it up into a little well a little cylindrical device that they can then can encapsulate and then it's a lot easier to use that in electronics but essentially it is if you then unroll them you have end up with two metal sometimes the foil metal plates that are very close together and also sometimes what we call a dialectric in between we'll talk about dialectric a little bit more later so the symbol we use for capacitors is one of these two depending upon the application and here we're simply going to get a feel for what a capacitor is and we have some definitions here a capacitor is a device that has the capacity to hold charge so that's the purpose of a capacitor you can put charge onto the capacitor you can hold it for a while and then give that charge back you could store energy you can do all kinds of things with capacitors a lot of good useful purposes for having a capacitor but essentially for the basic principle is that it can hold charge now the capacitance is the amount of charge a capacitor can hold some capacitors have a lot of capacitance small amount of capacitance and it depends upon how much voltage you apply to the capacitor so the equation that tells you what capacitance is it is equal to the charge divided by the voltage now the charge is the amount of charge you could put onto the plates they call that the charge collected on the plate and divided by the voltage applied so the More Voltage you have to apply in order to get charge on there the smaller the capacitance of the capacitor but if it just a small amount of voltage puts a lot of charge in the capacitor then the capacitor has a lot of room a lot of capacitors to put charge on there the unit we use is called the faret we use the letter f for that and the faret is defined as a Kum per volt that makes sense because charges in kums and volt is in voltage or volts is in voltage now notice that if you can put one colum of charge in a capacitor when you apply one volt the capacitance has the Capac the capacitor has the capacitance of one fet that's what that means but typically a coolum is a lot of charge and so normally on a capacitor you can only store a small fraction of a Kum when you apply a reason about a voltage on there so usually you don't see a lot of one farad capacitors although with modern technology they they've not been able to miniaturize the ability to store an enormous amount of charge on very small capacitors so they've actually come quite a way along with it the equation that we use to express what the Capac is based on its physical characteristics the physical Char characteristics would be the size of the plates the cross-sectional area the distance between the plates and on the Epsilon sub not is the permitivity of free space so now we're going to talk about capacitors that only have air between the plates later on we'll see how that equation changes when you actually put a dialectric in between the plates so what happens is you apply a voltage so this is what we call a voltage Supply or a power supply it pushes charges onto this one plate on one side which causes the positive charges on the other plate to be pushed away because of the repulsive forces causing this plate then to become negatively charged so for every positive charge you put on here a positive charge will come out here go to the negative side of the power supply and that one by one this becomes negatively charged as this becomes positively charged because you put extra positive charges there negative charge because you remove the positive charges and that's how you charge a capacitor it's the voltage or the power supply or the electromotive Force whatever you want to call it that pushes charges onto one plate that pushes away the same charge on the other plate and so now you have a disparity of charges that causes now a storage of charge that's how you store charge in capacitor uh notice that the Epsilon subn has this value right here and also notice that the units work out because Epsilon sub has units of Kum squ per Newton met squar area is me squar distance is meters and when you simplify that you end up with kums per volt which

### Segment 2 (05:00 - 05:00) [5:00]

of course again is the units for capacitance which we then call farad so that's basically understanding of what a capacitor is now let's go ahead and start showing you some examples of how to utilize that capacitor