Now that we’ve discussed both gasses and liquid fluids,
we’re ready to move on the electrical phenomenon
and this will include both electricity and magnetism
as well as how to apply electricity when it’s flowing through circuits.
Again as an overview, having covered fluids and gasses
and we did all the mechanics beforehand again,
which we will keep appealing to as we go.
We’re going to cover electricity and circuits and magnetism altogether
before moving on to some other different phenomenon
including waves and sound as well as some microscopic structure including atoms
as well as the thermodynamics of the smaller world.
We’ll start with electricity in circuits and magnetism.
The first thing we’ll do is cover some basic theory
on how we describe electricity, how we describe the forces between
different electrical objects and then we’ll get into some more complicated ideas
including fields and electric energy but first with the basic theory.
What we need to do is first describe electric charge
and what electric charge is and then we’ll talk about how electric charges attract each other
and what forces arise in those situations and that is Coulomb’s law,
and then finally we will talk briefly about the difference between
a conductor and an insulator but first, with electric charge.
There seems to be when we look around just huge amounts of energy
being moved around and we see it in a lightning storm
which is all coming from something but again, this energy is very, very powerful
and caused many people a very long time ago to ask, what is this?
What is causing not only what objects are doing this
but why are they moving and why is it so powerful?
Where’s all this energy, and heat, and light, and sound coming from?
It turns out, it’s coming from, if we looked very closely to matter,
we can see here a schematic of an atom.
In an atom we have a nucleus which is the central part of the atom
which we’ll be discussing in more detail later on,
but this nucleus has protons as well as neutrons.
Orbiting this nucleus we have what are called electrons
which are very tiny, tiny bits of matter
which have negative charge as opposed to the protons in the center of the atom
in the nucleus which have a positive charge.
We describe this charge in a very similar way which we described mass.
We’ll see some analogies between these two as we go forward.
We describe the charge with a symbol, q, instead of m for mass.
We measure in units of Coulombs and we use the letter C, a capital letter C,
as the abbreviation for the unit of coulombs.
This electric charge is basically trying to measure
how strongly an object experiences an electrical force
when it’s in the presence of other charged objects.
For the electron, what we have is q, the charge of the electron,
with a little letter e written below the q to indicate that we’re talking about an electron.
The charge of the electron is minus, it’s a negative charge, and this is just by convention.
There’s nothing about the physics of nature that requires us to call a positive or a negative charge that way.
It could have been the other way around
but for historical reasons the electron is called a negative charge
and the value of this negative charge is represented with a letter e
and the magnitude of that letter e is very small for one electron
and it is 1.6 times 10 to the minus 19th power coulombs.
Protons have a positive charge but it turns out the magnitude of this number is exactly the same.
It’s also 1.6 times 10 to the minus 19.
So electrons and protons have the same charge
even though they have very different sizes and therefore very different masses.
So, keep that in mind as we go forward that these charges are the same
having the same magnitude but one is negative and the other one is positive.
The last nucleon, the last object in the nucleus which is the neutron,
has no charge at all which is actually why we call it the neutron,
It is a neutral object and will not experience any of these electrical forces.
With these electron, proton, and neutron that we just described,
we can talk about the overall charge of an atom which is composed of more than one of these.
So, suppose we have a single proton in the center like this and it has orbiting it an electron,
this would be a hydrogen atom because it has one proton in the center
but because it has an electron orbiting it
and because we said that the electron and the proton are equal charges in magnitude
but opposite, one is positive and the other one is negative,
we say that the charge of this hydrogen atom is zero.
It’s a neutral hydrogen atom again because the charges are opposite.
If we added an electron for some reason,
if it adopted an electron because of its environment,
we would say that it is now negatively charged
because it has two negative charges while only having the one positive charge from the proton.
We have a name for charges like this which are anions.
We say a negatively charged ion is an anion.
One easy way to remember this might be to think of it as “A negative ion.”
It is an anion. On the other hand we could have the opposite thing happen maybe your atom,
this hydrogen atom, loses one electron.
In that case it no longer has any electrons while it still has this positive proton charge.
If that’s the case then the net charge of the atom as a whole
is now positive and we give it a different name which is a cation rather than an anion.
We only have the mnemonic for an anion so that one might be easier to remember
and just always remember the cation is the opposite. It’s positively charged.
There are few very important things to know about charge.
One is that charge is quantized.
What we mean by that is you cannot have a half of an electric charge or a 1.5 electric charges.
You have to come in discrete quantized units of charge.
Also, the charge must be an integer of this basic value that we saw which is e,
that very tiny number of the charge of the electron and the charge of the proton.
Finally, the total charge is conserved.
This charge can’t disappear anywhere
and nor can charge just come from somewhere in a given closed system.