Hi. It's Mr. Andersen and this is AP Physics essentials video 27. It is on electric field
strength. And before we start talking about that I am going to show you a quick simulation.
I am going to add some charges to a box. And the first time I add those charges I am going
to add 1 coulomb charges. And we are just going to watch their behavior. So each of
these particles has a 1 coulomb charge. You can see that they are pushing on each other.
Now let's increase the charge to 2 coulombs. And you should be able to realize that there
are bigger fields being generated. A greater electric field strength. Now we have a 3 coulomb
charge. They are really pushing on each other. You might have figured out that these are
positive charges because the fields are moving away from the charge. And now if we get a
5 coulomb charge, they are really applying a force to each other. There is a huge electric
field strength. This one charge can not even find a place to sit. And so if we take an
object, we can measure the electric field strength, and we usually represent that using
arrows. And so this object has no charge. But if I add a charge to it, it is going to
have an electric field that is moving out from that positive charge. If I remove the
charge then I remove that electric field. What is going to happen if I add a negative
charge? Well we are going to have the same size of arrows but now they are pointing towards
the charge by convention. If I remove the charge, what happens? They go away. Now this
video is about electric field strength. And so if I add one charge, to get an idea of
how long these arrows are, but now let me add one more charge. And what happens is we
have increased that electric field strength. And if I add another charge what happens?
Again we are increasing the electric field strength. It is getting large. And sometimes
it is unwieldily to just increase the size of those. So instead what we will do is as
we add more charges we just add more arrows. This will be important when we are looking
at, for example, two charged plates. And so we could represent the electric field strength
as arrows. And as we add charge we are increasing the number of those arrows. And so there is
a direct relationship between the charge of those plates and the electric field strength.
Now it is not always perpendicular, but we are just going to assume that these charged
plates are infinitely long. And so in this video we are really just trying to look at
one thing. And that is the relationship between the amount of charge and the electric field
strength. And so now I am going to use a phet simulation to look at how the amount of charge
affects the electric field strength. And we are going to use these electric field strength
testers around the outside. And I am just going to place charges right there in the
middle. It is a phet simulation. I would encourage you to play around with it. I will put a link
down below. So watch what happens when I add a positive charge in the middle. We have generated
an electric field. And as I increase the amount of charge, watch what happens to the electric
field strength. It is increasing. There is a direct relationship between the two. And
as I pull those charges out you can see that that electric field strength is going to 0.
What happens if we put a negative charge in the middle? You can see that we now have an
electric field. But those field lines are pointing towards the charge. As I increase
the number of charges, I am increasing the electric field strength. As I get rid of them
then the electric field strength is going away. But the neat thing about this simulation
is you can make it quantitative. So I am going to add a charge in the middle and then we
are going to turn on the numbers. You can see that each of these are measuring around
7 volts per meter. Watch what happens as I add a charge in the middle. Now they are all
measuring around 14 volts per meter. And now let's add one more charge. And what are we
going to get? It is going to be around 21 volts per meter. So there is a direct relationship
between the amount of charge and the electric field strength. And that is the one thing
you should have picked up. As we add charges we are going to increase the electric field
strength of that electric field. And it is a direct relationship between the two. And
I hope that was helpful.