Hey guys. In this video, we're going to be talking about a process known as dielectric breakdown. Let's get to it. We know that dielectrics are insulators and the insulators' charges can't move, right? Well, ideally, charges can't move. In reality, if you motivate them enough, if you provide, for instance, a large enough voltage, they will move across an insulator. It's very difficult, and it doesn't occur commonly, but it can occur. One such instance of this is a process known as dielectric breakdown. Just like the dielectric constant kappa is a fundamental quality of a dielectric, we have a second fundamental quality called the dielectric strength. And what the dielectric strength is, it's the maximum electric field supported within a dielectric before breakdown occurs. So if you go past that maximum electric field, past that dielectric strength, breakdown occurs. In dielectric breakdown, what we get is we get electrons jumping from atom to atom. Electrons can't exist freely within an insulator like they can in a conductor, so all they can do is move from one atom to another, when they reach the other atom, they sort of knock off the electron, that goes to another atom, that knocks off an electron, goes to another atom, etc., and eventually electrons cross the insulator like so. They sort of just jump from atom to atom until they cross the insulator. A very common example of dielectric breakdown is lightning. In a thunderstorm, we have some sort of thundercloud that through a process that we don't really know about, charges separate within this thundercloud. We're going to get an accumulation of positive charges near the top of the thundercloud and negative charges near the bottom of the thundercloud. On the ground, this is going to pull positive charges near the surface of the ground. And this separation of charges right here is going to act as a capacitor, where the air filling the space between is going to be our dielectric. And eventually, if the charge separation becomes large enough, the electric field becomes strong enough to pass the dielectric strength, breakdown occurs, and we get lightning.
Okay, let's do a quick example of this. A parallel plate capacitor is filled with air and connected to a power source of 100 volts. What is the closest you can put the plates together if dielectric breakdown of air occurs at an electric field of E=36 volts per meter? So E=36 volts per meter is the dielectric strength of air. Remember, for air, we're always going to treat the dielectric constant as 1. So the electric field, right, max is E=36 volts per meter. This is the dielectric strength. Well, within a parallel plate capacitor, the electric field is always going to be the voltage over the distance. So if we want to know the closest distance, all we have to do is divide the voltage by Emax. And the larger the electric field is, the smaller the distance. That's why we have the closest distance, the smallest distance for the largest electric field. This is going to be 100 volts over 36 which is going to be about 0.33×10⁻4 meters. That is our answer. Alright, this wraps up our discussion on dielectric breakdown. Thanks for watching.
