This video is about the idea of electric charge.
Charge is a property of matter that causes matter to experience the electrostatic force
from other charged objects.
The more charge the object has, the more force it will experience as the result of another
charge.
The variable we use for charge is "q" and the unit is "C" and it stands for "Coulomb"
who was a scientist associated with electricity.
So charges can be positive or negative.
Like charges repel each other and opposite charges attract each other.
So you'll remember by Newton's Third Law: if one charge puts a force on another, the
other will put the same force back on that first charge in the opposite direction.
So you can see by that picture on the bottom left that opposite charges attract by putting
equal and opposite forces on each other and like charges repel by putting equal and opposite
forces on each other.
Charge is also conserved: it cannot be created or destroyed, only moved from one object to
another.
There are only really two types of charged objects in the universe: the proton and the
electron.
All charge that we experience only exists because of the number of protons and electrons
in an object.
So there's no other source of charge in the universe.
It's just protons and electrons.
And protons and electrons have the same magnitude of charge but opposite sign.
So the charge of a proton is 1.602 x 10^-19 C, and the charge of an electron is the exact
same thing but an electron has a negative charge.
So we call this basic number the "elementary charge" because you can't get any smaller
than that.
You can't really get a charge that's smaller than that because all charges come from protons
and electrons, and there's nothing with a charge smaller than protons and electrons.
So all charges really just come in different amounts of the elementary charge.
So this means that the charge of an object must be a multiple of the elementary charge.
So you can have one proton or two protons of charge, but you can't have one and a half
protons of charge, that's not possible.
So because it comes in these very specific amounts or numbers, we say that charge is
"quantized" which is a physics way of saying that it comes in specific quantities and it
can't take values between those quantities.
Charge in an object comes from an imbalance between the protons and electrons in the atoms
that make the object up.
Just looking at this atom for example, you can see it has 4 protons and 4 electrons,
the electrons are in the outer shell.
So if I add up the charges here there are 4 positive and 4 negative elementary charges,
so the total charge on this object is zero.
If I take away one of the electrons you can see that it now has a positive charge that's
equal to the charge of 1 proton, because the 3 electrons are cancelling out the 3 protons
but there's 1 additional proton of charge, so the charge on this atom is now 1.602 x
10^-19.
And I can keep doing that, I can take away more, and you can see that as I take them
away the charge increases but it's increasing by the elementary charge.
It can't take a value between two elementary charges.
And so the most positive charge this atom can have is 4 times the elementary charge.
I can also add electrons and then it becomes negative.
This leads to a very important observation: electrons in an atom can move, and often leave
or join the atom.
So they're in the outer shell and they can leave the atom pretty easily and move to other
atoms.
Protons in comparison are "stuck" in the nucleus.
And therefore when the charge of an object changes, it's almost always because the electron
moved from one place to another, and almost never because the protons moved.
So therefore even when an object becomes positively charged, it is much more likely that this
was caused by losing negative charges, and not by gaining positive charges.
This is gonna be a really important concept.
Basically all changes in charge come from the movement of electrons, so even if something
becomes positive charged, what that actually means is that it lost negative charge.
It didn't gain additional positive charges from adding more protons.
One last note: you'll have to have a basic understanding of the difference between a
conductor and an insulator.
A conductor is any material that allows electrons to easily move through it, and an insulator
is any material that does not allow electrons to easily move through it.
Insulators can still be charged but the charges stick in place in the insulator and do not
move.
So common examples of conductors are things like most metals and water, and examples of
insulators are things like rubber, air, us (we ourselves are pretty good insulators),
wood, things like that, so on and so on.
So that's what you need to know about electric charge.