Electrodynamics/Tutorials/4/1/1
Video Intro
Hi, this is Jonathan Gardner.
We're covering [section reference] of Griffiths Introduction to Electrodynamics.
I'm going to move fast, but you can always rewind.
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As always, questions in a video response or comments.
Let's get started.
4.1 Polarization / 4.1.1 Dielectrics
Now that we have a solid grasp of how the math works for electric fields, potentials, and such, let's look at how these things behave in matter.
Remember we're talking about electrostatics still. That means we're not looking at how things behave when charges are moving around. We're only interested in how things are when all the charges have come to rest at equilibrium with each other and the environment.
We've already discussed conductors. In electrostatics, for the most part, the ideal conductor gives us a correct interpretation of reality. Some electric charges are not bound to the atoms, but can move freely around. This means that the electric field within the conductor is zero, the potential is constant, and the charge accumulates at the surface.
Insulators, also called dielectrics, are the other kind of matter when it comes to electrostatics. The key difference is that there is no free charge to roam around the material---at least in small electric fields. Turn up the field high enough, and the material changes to a conductor, ionizing it.
I like to imagine that dielectrics are made up of millions of tiny particles. Each particle is made up of a positive charge and a negative charge, attached to each other with a very strong, very short spring. Sometimes, in the absence of an electric field, these particles behave like a dipole because the charges do not line up exactly with each other. Other times, the two charges sit directly on top of each other, cancelling each other out without any dipole moment left over.
There are two kinds of effects applying an electric field to such matter can have. One, we can stretch the particles, pulling the two opposite charges apart. Two, we can make the particles turn to align with the electric field.
We're going to examine both of these in detail in the next videos.
