		Now, I'm sorry I got cut off on the last video.
		So let's talk a bit about the statics and the dynamics.
There are three static sources. There are static charges, there are
static permanent magnets like bar magnets, and there are static
currents. That means that the current is DC. The static charges
produce electric fields, the static permanent magnets produce
magnetic fields, and the static currents produce magnetic fields, but
if any of these are moving or changing with time, so for instance, if
the bar magnet is spinning and we spin it around like this, that makes
a magnetic field that is changing with time so H is time dependent or
if we take a current that is not DC such as an AC current, that is
going to make a magnetic field that is time dependent, and the really
cool thing about time dependent magnetic fields is that they produce
electric fields, and the electric fields that they produce are time
dependent, and the really cool thing that happens when you have time
dependent electric fields is that they produce time dependent
magnetic fields. So a time varying electric field produces a time
varying magnetic field which produces another time varying electric
field and so on.
		Here is an example of when that becomes very, very
interesting. Let's take your cell phone and let's use the old kind of
cell phone where the antenna sticks up like this. The current that we
send up the electric field that we send up the antenna produces a
magnetic field that's going around it in a circle like this. So there's
our magnetic field that's produced by the current. This current is a
sinusoidal and so it's time varying so that time varying magnetic field
produces a time varying electric field. The time varying electric field
it produces is parallel to the antenna so it creates a time varying
electric field which then of course produces a time varying magnetic
field which goes around in a circle which produces a time varying
electric field which produces a time varying magnetic field and a time
varying electric field and so on.
		This concept of dynamic fields, time varying electric and
time varying magnetic, is why antennas and other communication
devices work; it's why the fields no longer stay on the piece of metal,
that little piece of metal that wows your antenna. This is why
electromagnetics is so different than electro statics. It's when the
electric and magnetic fields become coupled, we call them coupled
when they produce each other, and it creates all of the unique
effects we're going to see in electromagnetics.
