November 4, 2019 • 44 mins
What's the difference between voltage and current? What is resistance? What are the units of measurement associated with electricity?
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Episode Transcript
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Speaker 1 (00:04):
Welcome to Tech Stuff, a production of I Heart Radios
How Stuff Works. Hey there, and welcome to tech Stuff.
I'm your host, Jonathan Strickland. I'm an executive producer with
I Heart Radio and I love all things tech and
in a recent episode, I talked about how scientists, doctors,
(00:24):
and philosophers had experimented with using the direct application of
electricity in an effort to treat various medical conditions. In
this episode, we're going to take a further step back
to understand the basics behind electricity itself. A lot of
this is going to be a refresher course from science classes,
primarily in physics, but it's to cover stuff that often
(00:47):
confuses people, and I'm including myself in that category. I
often get confused to the point where I frequently have
to do a quick refresher. So I'm not a scientist,
I'm not an electrical engineer. I have to remind myself
on the basics whenever I talk about electricity. Complicating matters
is that many text books for younger students in particular,
(01:07):
frame electricity in ways that can be misleading. They oversimplify
ideas to the point where they're kind of, you know, wrong,
and I know I've been guilty of doing the same
thing on this show. After all, I am a product
of the educational system that relies on such textbooks, and
I didn't have a background and electrical engineering. I know
(01:28):
I have on many occasions described electricity as the flow
of electrons, and that's not really the case. Now. Electrons
are charged sub atomic particles. They carry an electric charge.
But electricity, a vague term at best, isn't about these
carrier particles. It's more about the electric charge itself. So
(01:49):
I have to actually unlearn what I had learned to
talk about this more accurately. So if you're like me,
then this episode is going to be great for you.
And if you already know electricity inside and out, you'll
probably find this episode a little too basic for your liking.
Or in a worst case scenario, you might hear me
get something totally wrong. I'm working hard to prevent that,
(02:13):
but I am human. So if I say something totally wrong,
feel free to call me out on it, but please
just be nice about it. I am well intentioned, and
if I make a mistake, I want to correct it.
Just don't drag me under the bus for it, all right,
So Let's assume some of you out there are like
me and you don't have a background in working with electricity.
(02:37):
Let's figure out why this is so confusing. I mean,
we do have different units of measurement all to describe
various components of electricity and the behavior of electrical phenomena.
You know, we have whats, we have what hours or
more frequently, actually, really we have kill a lot hours.
We have volts, we have amps, we have ohms. It
(03:00):
can get a little overwhelming, so I'm gonna do my
best to try and clear stuff up a bit now.
In that medical history episode, I talked about Greek philosophers
who observed the effects of static electricity, what we call
static electricity, where you build up an electric charge and
it can be discharged when you come into contact with
(03:22):
something else, and about how Benjamin Franklin proved that this
was the same stuff as was found in lightning. But
I mostly stayed away from the history of detecting and
measuring electrical phenomena and the terminology that we associate with it.
So that's really what this episode will end up being about.
And in that previous episode, I mentioned that Benjamin Franklin
(03:43):
thought of electricity as a sort of fluid. He was
not alone in this. It was a prevalent thought at
the time, and that's probably why he described the movement
of electricity as current. But the way Franklin described current
and the way we tiply talk about electricity has caused
confusion for some folks like me. So I'll explain. Imagine
(04:07):
you have two pools of water and they're connected by
a hose. Now imagine that the ground is perfectly level
between these two pools of water. You would expect the
water in the hose to be pretty much in a
state of equilibrium. It would be still. But imagine one
pool is at a slightly higher elevation than the other. Well,
then you would expect water to follow the force of
(04:29):
gravity and flow down through the hose into the other pool.
You would have a current, and you could think of
the pool at the higher elevation as being positive, at
least in terms of elevation. So in that context, you'd
say that a current of water is flowing from positive
to negative through the hose. Now I'm oversimplifying a bit,
(04:51):
but that's kind of what Franklin was thinking. When it
comes to the fluid. He observed with electricity. He described
current as moving from positive to negative, and this has
more to do with the electrostatic experiments he was doing
and whether or not the surface that he was rubbing with,
for for example, was the positive or whether it was
(05:15):
the negative. You also have to remember that Franklin made
his observations more than a century before we had discovered
that electrons are even a thing that exists. I have
often joked that Franklin really messed us all up with
his description of current going from positive to negative, but
turns out that's not really true. Now explain why that
(05:36):
is in just a moment. Now, Later on after Benjamin
Franklin's time, we would learn more about electricity and we
began to learn about electric charges and electric potential. We
began to understand that you can have different magnitudes of
electric charge and it could be negative, it could be positive,
and that you can create a connection between different things
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with different electric charges and observe of a flow of
electric charge or an electric current. This was all stuff
that we learned over time. And let's think back on
our two pools connected by a hose analogy. If we
had two pools that were on level ground and we
equated that with a conductive pathway in an electrical circuit.
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Let's just say it's a it's a copper wire connecting
two terminals. Then we would describe that wires having equal
amounts of potential on either side. There's not a positive
and a negative terminal, they're both neutral, and in other words,
there's no difference in electrical potential. There's no difference in
potential energy, there's no flow of electrical charge, and thus
no electrical current. In the analogy in which we think
(06:43):
of one pool being at a higher elevation than the other,
we would describe the corresponding electrical system as the end
of the wire representing the elevator pool, elevator pool having
a higher potential energy or just higher potential, and the
lower end having a lower potential energy or lower potential,
And we call this difference an electric potential between the
(07:03):
high and the low pools as the voltage. So the
greater the difference between those two points in the analogy,
the greater difference in an elevation would mean the greater
the voltage. So if you have one that is one
terminal that's extremely positively charged and one that's extremely negatively charged,
you have an extreme voltage. The difference between those two.
(07:27):
Sticking with the analogy of water, voltage is like water pressure.
It's kind of how hard the electricity is being pushed
through the conductive connection between the different terminals. So if
the electric potential is of great magnitude, you get more pressure.
It's like a water hose shooting out water at high force,
(07:50):
like a fire hose connected to a fire hydrant. If
the electric potential isn't that great, if if the difference
isn't that great, then the voltage is lower, and in
our analogy, the water pressure is lower, so water would
come out and kind of a lazy arc as opposed
to blasting out at full force. And it helps if
we remember that opposite charges attract each other and like
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charges repel each other. So if there's a big difference
in electrical potential between two connected points, the like charges
are going to want to rush over to the opposite
charges and get the heck away from the other like charges.
If you listen to my previous episode, then you heard
me talk about Alessandro Volta, the man who invented the
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voltaic pile, which was a precursor to the modern battery.
He did that back in eighteen hundred. It's from his
name that we get volts and voltage, and a volt
is a unit of measurement to describe the difference in
electric potential between two points. I'll get back to describing
exactly how we define volts in a second, because unfortunately
(09:00):
that definition depends upon us knowing what some of this
other stuff is. First. It doesn't do you much good
to give a definition if you realize that all the
other terms in that definition are undefined. Okay, So if
we assume voltage is pressure water amps, Now, amps are
a measure of current, or how much electrical charge is
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flowing through a specific point in a circuit per unit
of time. So let's go back to the water analogy
and change things up a bit. Imagine that we have
those sets of pools we've been talking about. We have
one pool at a higher elevation and one pool at
a lower elevation. Now let's say that we copy that.
So now we've got to we've got two pools at
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high elevation, two pools at low elevation. With one of
the high low sets, we connect the two pools with
an ordinary garden hose, and with the other set, we
connect the two with a concrete tube with a much
greater diameter than the garden hose, more water will be
able to flow through a given point, Let's say it's
(10:04):
the midpoint of the concrete tube per unit of time
than through the midpoint of the garden hose in that
same unit of time. The concrete tube has a greater capacity,
The tube can hold more volume, and thus we get
more water coming out per unit of time than we
would observe with the hose. Well, with electrical circuits, we
described the same idea with amps. Amps tell us how
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much electrical charge passes a given point in a circuit
per unit of time. So voltage is the pressure and
amps or current is the amount of charge. Multiply those
two together and you get what's now. Moving back to Franklin,
we'll get back to Watson a second. He thought of
electricity as a positive flow, that the direction of current
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was in the direction of an electrical field, and unfortunately
we would later learn that it's the negatively charged electrons,
not the positively charged protons, that really move around in
a typical electric circuit. So if we follow the conventional
explanation of current. The flow of current is in the
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opposite direction of the flow of electrons. In a circuit
with a battery, we would see movement described as the
electrons going from the negative terminal of the battery through
a circuit doing whatever work was part of that circuit,
like lighting a lamp or something before journeying to the
positive terminal of the battery. But we would describe the
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current in that circuit as traveling from the positive end
of the battery through the circuit until it got to
the negative end. But what's more important here is not
the carrier of the electric charge. It's the concept of
electrical charge itself, not the movement of electrons, which again
are just the carriers. Electricity ultimately is about the flow
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of electric charge, positive or negative. So in our day
to day use of electricity, we're talking about of the
type where electrons flow through circuits, so we typically are
looking at negatively charged particles moving in a conductive pathway,
pushing that negative charge in the opposite direction of what
we would typically call the current. But electricity isn't the
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movement of electrons, even though that's often how it is simplified.
It's really the movement of the charge itself we need
to be concerned with. And if you have a flow
of protons, you would still have a flow of charge,
and thus you would still have electricity. So a particle accelerator,
for example, the accelerates a beam of protons is creating
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a flow of electricity. Electrons are not even involved in that.
It's the movement of positively charged particles. You're getting a
movement of a positive charge that is technically electricity. So
again we need to kind of divorce ourselves from the
idea of electrons and think more about electrical charge. The
electrons happen to be the carriers of that, but that's
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as far as their importance is concerned from this perspective.
They get important again once we start talking about quantum effects,
but that's a discussion for a different time. So I
say all this in order to exonerate Benjamin Franklin a
little bit. I give him a hard time, but it's
largely because the way we harness electricity for most of
the stuff we do means that we have an apparent
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contradiction in the sense of the flow of electrons and
the flow of current. But to be fair, our lay
understanding of electricity is based on a lot of misconceptions.
In general, we focus a bit too much on those
carrier particles and not the larger concept of electric charge.
Another misconception has to do with the wires in a circuit.
I'll explain more after we take a short break. Okay,
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so let's get another misconception out of the way. Many
people take that analogy of water pipes or hoses or
tubes as being a literal one to one with electricity,
and thus the wires in a circuit they think of
as empty conduits through which electrons can travel like. They're
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imagining the wires as being these hollow tubes, and electrons
are just shooting down the tubes. They're coming out of
the battery or out of the wall if you have
something plugged in, shooting down the tube and getting to
the other end. But if we think about that for
even a moment, we realize that cannot possibly be true,
because the wires themselves are made up of atoms, and
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atoms have electrons. So it's more like a tube or
a hose or whatever that is already packed with water
before you connected to the two pools. And even that
is not a perfect analogy. So let's talk about conductivity.
Some types of atoms have electrons in their outer energy
levels that are more lucy goosey. If you have a
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single copper atom, then you've got a nucleus that contains
twenty nine protons and thirty five neutrons. Now we're talking
about a basic neutral copper atom, meaning the positive and
negative charges cancel each other out. So we have twenty
nine electrons paired up with that nucleus that has twenty
nine protons. Electrons orbit the nucleus, but not in the
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same way that planets orbit stars or moons orbit planets.
The electrons inhabit various orbitals, which in turn are in
what we would call subshells, which are in shells around
the nucleus. Now I'm not going to dive into all
of that, because I'm sure most of you have a
general handle on it. But the twenty nine electrons and
copper add up to a point where one electron is
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left orbiting the outermost shell. There's no room for that
last electron in any of the lower shells closer to
the nucleus, so this electron is pushed out to the
next lowest energy shell, and it's they're all by its lonesome.
That means that electron is easier to push around than
the ones that are locked in packed closer to the nucleus.
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So when you lump a bunch of copper atoms together,
like that was just one copper atom, right, If we
put a bunch of copper atoms together and we've got
something like a copper wire that's made up of trillions
of these atoms, you end up with a mass of
copper atoms that all have these single free electrons, and
you can almost think of those electrons as moving around
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the mass of copper atoms as opposed to being tied
down to a single copper nucleus. If you then connect
the wire into a circuit in which you have a
battery or some sort of generator or something, that battery
or generator acts as a pump that can push those
free electrons around. The negative terminal has a charge that
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pushes against those electrons because remember like charge repels like,
so each of those electrons has its own negative charge
and pushes further down the path of the circuit. And
since since the other end of the battery has a
positive terminal, the negative charges get attracted to the positive side.
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It's not that electrons are shooting out of a battery
down a pipe, doing some work, and then going into
the other end of the battery. Is that the charge
of the battery is pushing through this pathway and the
electrons carry that charge. Likewise, the electrons are not moving
at the speed of light. I know I've been guilty
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of saying that before too, but that's not correct. The
electrons move much more slowly than the speed of light.
You could even say the charge moves more slowly than that.
But within the circuit, the charge is moving throughout all
parts of the circuit at the same time. It's not
like one electron moves and then the next one and
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then the next one. It's like they're all moving together
in in lock step. And so you have this entire
circuit that all goes into motion at the same time.
And to us that means that we see practically instantaneous results.
So if you flip on a light switch to an
incandescent lamp, the light comes on immediately, it doesn't delay.
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That's why. It's because all of those electrons in the
circuit are moving at the same time, so the effect
is that it's moving at the speed of light. But
in reality, what's actually happening is the electrons as a
whole in this circuit are all moving together. So a
battery connected to a circuit is not really a source
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of electrons. It's a source of energy. It's providing the
energy or the pressure to move that charge through the circuit.
It's the source of voltage. An electrochemical reaction in the
battery acts as an internal circuit to create this voltage,
which manifests as a difference in electrical potential shold between
the positive and the negative terminals on the battery. Connecting
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that battery to a circuit is what gives the energy
necessary to move this charge through the circuit and to
do whatever work it is you need to do along
the way, such as lighting up that light bulb. Within
a battery, you've got an exothermic reaction that is working
against the electric field. So it's kind of like pushing
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a boulder uphill. The force of gravity in that case
would be working against you and you have to overcome it.
You have to exert effort to work against the force
of gravity to push the boulder up the hill. A
battery likewise is exerting effort in the form of this
exothermic reaction. The external circuit, that is, the larger circuit
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that you connect to the battery, is following the natural
energy field. It isn't working uphill. It's got a high
potential terminal and a low potential terminal, and the current
flows according to the direct and of high to low
as Franklin described, The actual electrons are going in the
opposite direction. As the charge moves through the circuit, it
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encounters energy transforming devices. These would be things like light bulbs,
heating elements, pretty much, you know, anything that you would
connect to a circuit. At those points, some of the
electrical potential energy of the charge gets transformed into some
other form of energy, light, heat, whatever. The loss of
electrical potential in a circuit after passing through one of
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these elements is often called a voltage drop. Now going
to the water analogy again, imagine that you have a
pool of water. You have a ramp set up above
that pool of water, like maybe it's like a water slide,
and the water slide is not turned on, uh, and
it's smacked aub in the middle of the pool. You're
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also in the middle of the pool, and you grab
a bucket and you fill it up with water from
the pool. You lift the bucket up over your head
to the top of the slide, and you tip the
bucket out so that the water hits the slide, goes
down the slide off the other end back into the pool. Well,
you've just taken water from an area of low potential
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energy in this case, kinetic energy, and you moved it
using work to an area of high potential energy. The
water then flows down the ramp till it gets the end.
And maybe you even put a water wheel at the
base of this slide, so when the water hits the
water wheel, it actually provides the work necessary to turn
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the wheel and you get the wheel turning. You have
this display of mechanical energy from the water. So that's
kind of what you would see with a battery in
a circuit. In this example, you are fulfilling the same
purpose of a battery. You are lifting some water using
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work from an area of low potential to an area
of high potential. The battery is doing this but with
electrical potential, not with you know, physical stuff. Okay, now
it's time to define an actual vault. I alluded to
this in the first segment of this podcast. We've got voltage,
which is this difference in electrical potential between two points.
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And we understand that creating a conductive path between an
area of high electrical potential and one of low electrical
potential allows for the flow of current. So how do
we define a vault. Well, there's actually a couple of ways.
One is to say that one volt is equivalent to
the energy consumption of one jewel per electric charge of
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one coolomb. But that just raises more questions, doesn't it.
The dictionary definition of a jewel is a unit of
work or energy equal to the work done by a
force of one Newton acting through a distance of one meter,
and a Newton is a unit of force. One Newton
is the force required to impart an acceleration of one
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meter per second per second to a mass of one
kim okay, So a jewel is the energy required to
produce a Newton's worth of force through a distance of
one meter. What's a coulomb. A coulomb is a unit
of electrical charge equal to the quantity of a current
of one ampier in one second. It's named after Charles
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Augustine de Coulomb, who in the late seventeen hundreds developed
a description of the force that interacts between electrical charges.
He had determined that like charges repel each other and
that opposite charges attract each other, and his work led
to further discoveries that the force of this repulsion or
attraction is proportional to the products of the electrical charges
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and inversely proportional to the square of the distance between
those two charges. And this is what we now call
Coulomb's law and another way to define volt That was
one way, but here's the other one. It's equivalent to
one amp of current times the resistance of one ohm.
And oh my goodness, looks like we're gonna have yet
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another thing to talk about here. And while you might
hear that resistance is useless, I'm here to tell you
it's pretty important in the case of circuitry. So I
talked about how copper is a good conductor because of
those free electrons, right well, the single electrons in the
outermost energy shell around a copper nucleus make copper a
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great conductor of electricity. We describe this quality of copper
as conductance, or the ease with which electrical current may
pass through that substance. The opposite quality is called electrical resistance,
the opposition of a material to the flow of current
through it, And typically we talk about that with materials
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that have fewer or no free electrons, making it more
difficult for electricity to pass through. Even copper has some
electrical resistance. It's not a perfect conductor, at least not
under conditions you and I would typically experience. Resistance is
kind of like the concept of friction, right. We know
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that an object in motion tends to stay in motion.
So if you were to roll a ball across a
perfectly level surface, and both the ball and that surface
were made of some magical material that ignored friction, there's
no friction in this system, then that ball would roll
forever unless it ran into something. But friction means that
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some of the energy of that rolling ball in a
normal setting where we're using you know, a real ball
and a real level surface, friction means that some of
that energy gets converted into heat, and that means that
there's less energy for that ball to continue to roll,
and eventually the ball will slow down and stop rolling.
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Electrical resistance is kind of similar to that typically we
see energy and electrical circuits convert into other forms like heat,
which dissipate into the environment at large. Now I mentioned
that one volt is equal to one amp of current
running through one ohm of resistance. Resistance then is the
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ratio of voltage across whatever material we're talking about, divided
by the current going through that material. So resistance is
voltage divided by current, and conductance is the current running
through an object divided by the voltage across it, So
it's the reciprocal of resistance. Now we measure resistance in
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oms and ohm is the amount of electrical resistance between
two points on a conductor when there's a constant potential
difference of one volt applied to those points, producing one
current or one amp here of current. I should say
electrical resistance depends on a lot of stuff. Depends upon
the atoms of the material itself, So the resistance of
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a copper wire will be different than the resistance of
say a gold wire that's of the same thickness or gauge.
It also depends upon the thickness or gauge of a wire,
so a thicker copper cable will have less resistance than
a thin copper wire. And it depends upon stuff like temperature.
If you were to super cool some conductors, like get
(27:26):
it near absolute zero, they would then have them perform
as super conductors, which is material that can conduct current
with no conversion into other types of energy like heat.
You get no loss. In other words, likewise, there are
some materials that have tightly packed electrons that resist this
flow of current. I mentioned those earlier. We would call
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these insulators. So materials that insulate don't allow for the
conduct conductivity of electricity or they severely restricted. Alright, so
quick rundown voltage is akin to pressure. It's the difference
in electrical potential between two points. Amperage is a measurement
of current and explains how much charge passes a given
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point in a circuit within a unit of time. Ohms
are a measure of resistance, or how much material resists
the flow of charge through it. Now to define a what,
so a what is the amount of electrical work performed
when one ampere of current flows across one volt of
electrical potential difference? So what is a unit of power?
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And this is where I find another stumbling block for myself,
because in language we often swap out words that have
similar meanings in other contexts, but very specific meanings in physics,
and it causes confusion for people like me. So words
like work, energy, power, and force they get thrown around
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a lot, and it's easy to forget what they all
mean within the context of physics, and they mean different things.
A force is something that causes an object to change
its velocity in some way. Velocity is a vector quantity
that means it has both a magnitude and a direction.
So in our example of rolling a ball on a
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flat surface, that ball would tend to stay in motion
at a constant speed and remain on a straight path
on its own unless some other force were to act
upon that ball and either speed it up or slow
it down, or make it change its direction, or some
combination of these things. That would be an external force
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acting upon this system. You can think of energy as
the capacity for doing work, and it comes in lots
of different forms. A moving object has kinetic energy. For example,
work is a type of energy, specifically the amount of
energy used to apply some force on some object over
(30:03):
some distance. Now, as I mentioned earlier, the jewel is
a unit of energy defined as being equal to the
work done by a force of one newton across one
meter in the direction of action of that force. We
would describe the energy needed to lift a kilogram and
move it a meter in a specific direction as work.
(30:24):
Power is a description of the amount of energy used
per unit of time. So if you expend twelve jewels
of energy to do some sort of work, Let's say
it's to to move a wheelbarrow a few feet. Uh,
let's say that's that's how much energy you spent total
moving that wheelbarrow. This is a totally hypothetical example. So
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you spent twelve jewels moving it. If you expended that
energy those twelve jewels over the course of three seconds,
your average output of power would be for watts. As
you take the twelve jewels that you took to actually
do this thing and the three seconds the amount of
time it took you to do it, and you divide
(31:06):
the twelve by the three, that's where you get the
four watts. When we come back, I'll talk a little
bit more about volts, amps, watts and how to read
your power bill. But first let's take another quick break.
(31:27):
I mentioned that one what is the same as one
jewel of energy expended in one second. So what does
it mean if your power bill is broken down by
kill a watt hours. Well, it's kind of simple, and
that a kill a watt hour is what it sounds like.
It's the equivalent to one kill a watt of power
(31:48):
sustained over the course of an hour of time. Since
and this is a unit of energy, right, Since since
one what is equivalent to a jewel per second? A
kill a lot hour is equal to three point six
mega jewels. Wait, how did I get that number? Well,
jewel per two. Right, there are sixty seconds in a
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minute and sixty minutes in an hour, so we multiply
sixty by sixty to get us three thousand, six hundred
that's how many seconds there are in an hour. Then
we multiply that by one thousand because we have one
thousand watts because it's at kill a lot, So one
thousand watts times three thousand, six hundred seconds we get
three point six million. And remember a what is equivalent
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to one jewel per second? That means a jewel is
equal to what's times seconds, So one thousand watts per
hour three pint six mega jewels are equal. We use
kill a wat hours to describe the amount of energy
used to do work. So let's say you've got an
appliance at home that requires a kill a lot in
order for it to do its work. So it's gonna
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have a kill a lot of work in order to
do whatever it's doing. Let's say it's an air conditioner.
You gotta kill a what air conditioner. If you run
that appliance for one hour, it consumes one kilowatt hour
worth of energy to do that work. If you have
a ten what device plugged in, it would take that
device one hundred hours for it to use one kilowatt
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hour of energy. Power companies usually sell electrical energy in
kilowatt hours, and it gets more confusing than that. Some
regions have varying prices on kilowatt hours. Sometimes that price
depends upon the time of day or the rate of consumption.
So we're just going to leave it at that. But
that's why we're talking about kilowatt hours as units, and
(33:38):
you're really thinking about this is the amount of energy
that is representative of doing a killer what worth of
work within an hour. I haven't talked about direct current
and alternating current yet, so I guess I should do that.
A bit direct current is what you would find in
a circuit connected to a battery. The direction of current
(33:58):
is always going to stay the same because the positive
and negative terminals on the battery are fixed. They can't swamp.
The positive terminal is always positive. The negative terminal is
always a drag guy. He's just always saying bad things
about everybody. Alternating current switches the terminals in a circuit,
and thus the direction of current switches back and forth,
(34:22):
and it does this in cycles per second. So in
Europe the standard is fifty times per second fifty cycles.
In the United States it's sixty cycles per second. The
reason we use alternating current is largely because of how
it's pretty easy to adjust voltages for the purposes of
power distribution. This is where things like resistance and voltage
(34:48):
and ambridge really become important. So let's say you've got
a power plant and that power plant produces one million
watts of power. But then you have to distribute that
power to the people who need it and the places
that need it. So how do you do that. Well,
you could send one million amps at an electrical potential
(35:09):
difference of one volt, because remember the watts are it's
really volts times amps. So if you have a million amps,
then your voltage has to be one or you could
send one amp very low current across an electrical potential
difference of a million volts. One amp would only need
(35:30):
a very thin wire. It doesn't need much wire at
all and would have very little energy loss due to heat.
A million amps would need an incredibly thick cable to
avoid losing too much energy to resistance or burning through
the wire entirely. And it would be very tricky to
come up with a method that works for both distributing
electricity across vast distances and also making use of that
(35:55):
electricity once it gets to the home. Like once you
get to the home, you don't probably want a super
high current in your home. It would burn out all
of your electrical appliances and probably kill you. Uh. You
also don't want super low current for like super super
low current, and you don't you know your voltage. You
(36:16):
don't need super high voltage for the home. So how
do you solve that problem? Well, direct current has issues
with that. Alternating current, however, allows for the use of transformers,
which lets you step up or step down the voltage.
Now I've talked about transformers in other episodes, so I'm
not going to go through all of that right now,
(36:38):
but they are how a power company can increase or
decrease the voltage. They can increase the voltage for the
purposes of transmission, where transmitting power at high voltage is
more efficient less power loss. You can push it further
distances and then step it down when it comes time
to distribute that power to read and so you step
(37:02):
it up for the purposes of transmission. It gets to
say a neighborhood, it goes to a different transformer that
steps the voltage back down a bit, and then that
transformers sends the power over to the households, where there's
another step down to get it down to the standard
in that house. So in the United States, that standard
(37:23):
is one volts, all right, So really it's to make
it more confusing, a pair of wires that combined offer
two hundred forty volts of power, but that's because of
alternating current. Most homes have an electrical service that provides
between a hundred to two hundred amps, though there are
exceptions both on the low end and the high end.
(37:44):
There's more I could go into with direct current versus
alternating current, including obviously the current wars between Westinghouse and Edison.
A lot of people say between Tesla and Edison, although
I think that's not entirely fair, uh, And I can
also talk about the equations used to describe direct current
versus alternating current. They are a bit different. But I'm
(38:05):
going to hold off on all of that for a
future episode because otherwise this episode would run way too
long for me to get into that. Something else I
did want to cover, however, was the difference between voltage
and amperage when it comes to safety risks. Now we've
established that these two factors are different. Voltage and ambridge
(38:26):
described different things. Voltage again, is that pressure and ambridge
is the amount of charge passing through a given point
in a given amount of time. But which is more dangerous?
Which one do you need to be more aware of? Well,
you've probably seen signs that say things like danger high
voltage when there's a fire at the disco or a
fire at the taco bell. Make sure you let me
(38:49):
know if you actually get that reference. It might just
be making a joke for my own sake at that point.
But is voltage the really dangerous factor here. Well, it's
a bit more complicated than that. Let's say you encounter
a current running at high voltage but very low ambridge,
so there's a lot of pressure in the line, but
(39:09):
not much electrical charge being moved through per second. That
would be less dangerous than a current a high current
with a relatively low voltage, So a high ambridge low
voltage would be more dangerous than a high voltage low ambridge,
And it doesn't take much amperage to do some damage
to us. When you get a zapp from an electrostatic charge,
(39:34):
chances are the brief current would have measured in the
one to ten milla amp range, So a mill hamp
is one of an amp. Less than that you probably
would even feel it, and one to ten you would
feel the little snap of an electric spark, but you
wouldn't have any muscular convulsion at that strength of ambridge.
(39:56):
Electro Static charges are are very high voltage but very
low ambridge. At about ten milli amps of current, you
would experience muscular contractions. If you grabbed hold of a
wire that had ten or more milla amps of current
running through that wire, you'd probably find yourself unable to
let go. As you got shocked, your muscles would clamp down.
(40:20):
At about twenty milla amps of current, you'd find it
difficult to breathe. If the current were around one hundred
miller amps, it would probably be fatal as it would
interfere with the operation of your heart. And it might
seem counterintuitive, but above two hundred milli amps you could
actually survive the experience. So between one and two hundred
(40:43):
is the real danger spot. Your heart would go into
uncoordinated contractions and you would experience was called ventricular fibrillation,
and that in fact can be fatal. Above two hundred
mill amps, your heart would actually seize up. It would
affect to really act as if it had been clamped down,
so it wouldn't go into ventricular fibrillation, it wouldn't have
(41:06):
those uncontrolled contractions. It would just stop. And if someone
were able to shut down the current going through you
fast enough, you could probably be revived. After that, you
could be given resuscitation and recover. You would probably have
some nasty burn injuries to deal with, and you would
probably also have some injuries and and damaged to your
(41:28):
internal organs. I have more to say about that in
an episode about the electric chair, where we did it
to people on purpose and continue to in some cases.
So that's the key there is that you really want
to be aware of the amperage and voltage is still important.
It's not like it's pleasant to get zapped by a
(41:50):
low amperage high voltage electric current, but it's not as
dangerous as the the amperage would be. And it's those
tiny little changes an amperage that will get you. So
be aware. Now I'll have to do more episodes to
talk about stuff like diodes, triodes, capacitors, and other components
(42:14):
in circuitry. I've covered them in previous episodes, but I
feel like taking this approach and really breaking it down.
Getting to the basics builds upon an understanding that we
can then rest more complicated subjects upon. Right, you can
start once you start understanding how these circuit pathways work
(42:35):
and what they do, and the behavior of electrical charge
and why that's important. Then you can build on that
and include things like quantum effects and why it gets
difficult when you start getting into concepts like logic gates
and quantum tunneling. You can you can touch on those subjects.
(42:57):
You can also understand what a logic gate is, and
you can understand how to build circuits to do actual,
you know, tasks like how you can create a circuit
to do calculations. But it all depends upon this basic
understanding of what is going on with these electrical charges.
And I find that if we start there we can
(43:21):
build a better understanding of everything else as we go along.
But that's gonna be for a later episode. Our next
one is going to be about using electricity to kill you.
I didn't. I did one on how people try to
use electricity to help you, and that continues to this
day to varying degrees of success in scientific rigor. And
then we're gonna talk about the other extreme in our
(43:44):
next episode, a pleasant topic to say the least, and
then after that we'll cover all sorts of stuff. I
haven't decided what goes on after that one, but if
you guys have suggestions for things I should cover in
future episodes of tech Stuff, you can reach out via
email The addresses tech Stuff at how stuff works dot com,
or you can reach out via social media. It's tech
(44:07):
Stuff hs W both on Facebook and on Twitter, and
go on over to our website. That's tech stuff podcast
dot com. You'll find a link to the archive of
all of our past episodes. You also find a link
to our online store, where every purchase you make goes
to help the show and we greatly appreciate it, and
I will talk to you again really soon. Text Stuff
(44:34):
is a production of I Heart Radio's How Stuff Works.
For more podcasts from I heart Radio, visit the I
heart Radio app, Apple Podcasts, or wherever you listen to
your favorite shows.
Welcome to Tech Stuff, a production of I Heart Radios
How Stuff Works. Hey there, and welcome to tech Stuff.
I'm your host, Jonathan Strickland. I'm an executive producer with
I Heart Radio and I love all things tech and
in a recent episode, I talked about how scientists, doctors,
(00:24):
and philosophers had experimented with using the direct application of
electricity in an effort to treat various medical conditions. In
this episode, we're going to take a further step back
to understand the basics behind electricity itself. A lot of
this is going to be a refresher course from science classes,
primarily in physics, but it's to cover stuff that often
(00:47):
confuses people, and I'm including myself in that category. I
often get confused to the point where I frequently have
to do a quick refresher. So I'm not a scientist,
I'm not an electrical engineer. I have to remind myself
on the basics whenever I talk about electricity. Complicating matters
is that many text books for younger students in particular,
(01:07):
frame electricity in ways that can be misleading. They oversimplify
ideas to the point where they're kind of, you know, wrong,
and I know I've been guilty of doing the same
thing on this show. After all, I am a product
of the educational system that relies on such textbooks, and
I didn't have a background and electrical engineering. I know
(01:28):
I have on many occasions described electricity as the flow
of electrons, and that's not really the case. Now. Electrons
are charged sub atomic particles. They carry an electric charge.
But electricity, a vague term at best, isn't about these
carrier particles. It's more about the electric charge itself. So
(01:49):
I have to actually unlearn what I had learned to
talk about this more accurately. So if you're like me,
then this episode is going to be great for you.
And if you already know electricity inside and out, you'll
probably find this episode a little too basic for your liking.
Or in a worst case scenario, you might hear me
get something totally wrong. I'm working hard to prevent that,
(02:13):
but I am human. So if I say something totally wrong,
feel free to call me out on it, but please
just be nice about it. I am well intentioned, and
if I make a mistake, I want to correct it.
Just don't drag me under the bus for it, all right,
So Let's assume some of you out there are like
me and you don't have a background in working with electricity.
(02:37):
Let's figure out why this is so confusing. I mean,
we do have different units of measurement all to describe
various components of electricity and the behavior of electrical phenomena.
You know, we have whats, we have what hours or
more frequently, actually, really we have kill a lot hours.
We have volts, we have amps, we have ohms. It
(03:00):
can get a little overwhelming, so I'm gonna do my
best to try and clear stuff up a bit now.
In that medical history episode, I talked about Greek philosophers
who observed the effects of static electricity, what we call
static electricity, where you build up an electric charge and
it can be discharged when you come into contact with
(03:22):
something else, and about how Benjamin Franklin proved that this
was the same stuff as was found in lightning. But
I mostly stayed away from the history of detecting and
measuring electrical phenomena and the terminology that we associate with it.
So that's really what this episode will end up being about.
And in that previous episode, I mentioned that Benjamin Franklin
(03:43):
thought of electricity as a sort of fluid. He was
not alone in this. It was a prevalent thought at
the time, and that's probably why he described the movement
of electricity as current. But the way Franklin described current
and the way we tiply talk about electricity has caused
confusion for some folks like me. So I'll explain. Imagine
(04:07):
you have two pools of water and they're connected by
a hose. Now imagine that the ground is perfectly level
between these two pools of water. You would expect the
water in the hose to be pretty much in a
state of equilibrium. It would be still. But imagine one
pool is at a slightly higher elevation than the other. Well,
then you would expect water to follow the force of
(04:29):
gravity and flow down through the hose into the other pool.
You would have a current, and you could think of
the pool at the higher elevation as being positive, at
least in terms of elevation. So in that context, you'd
say that a current of water is flowing from positive
to negative through the hose. Now I'm oversimplifying a bit,
(04:51):
but that's kind of what Franklin was thinking. When it
comes to the fluid. He observed with electricity. He described
current as moving from positive to negative, and this has
more to do with the electrostatic experiments he was doing
and whether or not the surface that he was rubbing with,
for for example, was the positive or whether it was
(05:15):
the negative. You also have to remember that Franklin made
his observations more than a century before we had discovered
that electrons are even a thing that exists. I have
often joked that Franklin really messed us all up with
his description of current going from positive to negative, but
turns out that's not really true. Now explain why that
(05:36):
is in just a moment. Now, Later on after Benjamin
Franklin's time, we would learn more about electricity and we
began to learn about electric charges and electric potential. We
began to understand that you can have different magnitudes of
electric charge and it could be negative, it could be positive,
and that you can create a connection between different things
(05:57):
with different electric charges and observe of a flow of
electric charge or an electric current. This was all stuff
that we learned over time. And let's think back on
our two pools connected by a hose analogy. If we
had two pools that were on level ground and we
equated that with a conductive pathway in an electrical circuit.
(06:20):
Let's just say it's a it's a copper wire connecting
two terminals. Then we would describe that wires having equal
amounts of potential on either side. There's not a positive
and a negative terminal, they're both neutral, and in other words,
there's no difference in electrical potential. There's no difference in
potential energy, there's no flow of electrical charge, and thus
no electrical current. In the analogy in which we think
(06:43):
of one pool being at a higher elevation than the other,
we would describe the corresponding electrical system as the end
of the wire representing the elevator pool, elevator pool having
a higher potential energy or just higher potential, and the
lower end having a lower potential energy or lower potential,
And we call this difference an electric potential between the
(07:03):
high and the low pools as the voltage. So the
greater the difference between those two points in the analogy,
the greater difference in an elevation would mean the greater
the voltage. So if you have one that is one
terminal that's extremely positively charged and one that's extremely negatively charged,
you have an extreme voltage. The difference between those two.
(07:27):
Sticking with the analogy of water, voltage is like water pressure.
It's kind of how hard the electricity is being pushed
through the conductive connection between the different terminals. So if
the electric potential is of great magnitude, you get more pressure.
It's like a water hose shooting out water at high force,
(07:50):
like a fire hose connected to a fire hydrant. If
the electric potential isn't that great, if if the difference
isn't that great, then the voltage is lower, and in
our analogy, the water pressure is lower, so water would
come out and kind of a lazy arc as opposed
to blasting out at full force. And it helps if
we remember that opposite charges attract each other and like
(08:14):
charges repel each other. So if there's a big difference
in electrical potential between two connected points, the like charges
are going to want to rush over to the opposite
charges and get the heck away from the other like charges.
If you listen to my previous episode, then you heard
me talk about Alessandro Volta, the man who invented the
(08:37):
voltaic pile, which was a precursor to the modern battery.
He did that back in eighteen hundred. It's from his
name that we get volts and voltage, and a volt
is a unit of measurement to describe the difference in
electric potential between two points. I'll get back to describing
exactly how we define volts in a second, because unfortunately
(09:00):
that definition depends upon us knowing what some of this
other stuff is. First. It doesn't do you much good
to give a definition if you realize that all the
other terms in that definition are undefined. Okay, So if
we assume voltage is pressure water amps, Now, amps are
a measure of current, or how much electrical charge is
(09:21):
flowing through a specific point in a circuit per unit
of time. So let's go back to the water analogy
and change things up a bit. Imagine that we have
those sets of pools we've been talking about. We have
one pool at a higher elevation and one pool at
a lower elevation. Now let's say that we copy that.
So now we've got to we've got two pools at
(09:42):
high elevation, two pools at low elevation. With one of
the high low sets, we connect the two pools with
an ordinary garden hose, and with the other set, we
connect the two with a concrete tube with a much
greater diameter than the garden hose, more water will be
able to flow through a given point, Let's say it's
(10:04):
the midpoint of the concrete tube per unit of time
than through the midpoint of the garden hose in that
same unit of time. The concrete tube has a greater capacity,
The tube can hold more volume, and thus we get
more water coming out per unit of time than we
would observe with the hose. Well, with electrical circuits, we
described the same idea with amps. Amps tell us how
(10:27):
much electrical charge passes a given point in a circuit
per unit of time. So voltage is the pressure and
amps or current is the amount of charge. Multiply those
two together and you get what's now. Moving back to Franklin,
we'll get back to Watson a second. He thought of
electricity as a positive flow, that the direction of current
(10:48):
was in the direction of an electrical field, and unfortunately
we would later learn that it's the negatively charged electrons,
not the positively charged protons, that really move around in
a typical electric circuit. So if we follow the conventional
explanation of current. The flow of current is in the
(11:08):
opposite direction of the flow of electrons. In a circuit
with a battery, we would see movement described as the
electrons going from the negative terminal of the battery through
a circuit doing whatever work was part of that circuit,
like lighting a lamp or something before journeying to the
positive terminal of the battery. But we would describe the
(11:30):
current in that circuit as traveling from the positive end
of the battery through the circuit until it got to
the negative end. But what's more important here is not
the carrier of the electric charge. It's the concept of
electrical charge itself, not the movement of electrons, which again
are just the carriers. Electricity ultimately is about the flow
(11:53):
of electric charge, positive or negative. So in our day
to day use of electricity, we're talking about of the
type where electrons flow through circuits, so we typically are
looking at negatively charged particles moving in a conductive pathway,
pushing that negative charge in the opposite direction of what
we would typically call the current. But electricity isn't the
(12:16):
movement of electrons, even though that's often how it is simplified.
It's really the movement of the charge itself we need
to be concerned with. And if you have a flow
of protons, you would still have a flow of charge,
and thus you would still have electricity. So a particle accelerator,
for example, the accelerates a beam of protons is creating
(12:38):
a flow of electricity. Electrons are not even involved in that.
It's the movement of positively charged particles. You're getting a
movement of a positive charge that is technically electricity. So
again we need to kind of divorce ourselves from the
idea of electrons and think more about electrical charge. The
electrons happen to be the carriers of that, but that's
(13:00):
as far as their importance is concerned from this perspective.
They get important again once we start talking about quantum effects,
but that's a discussion for a different time. So I
say all this in order to exonerate Benjamin Franklin a
little bit. I give him a hard time, but it's
largely because the way we harness electricity for most of
the stuff we do means that we have an apparent
(13:23):
contradiction in the sense of the flow of electrons and
the flow of current. But to be fair, our lay
understanding of electricity is based on a lot of misconceptions.
In general, we focus a bit too much on those
carrier particles and not the larger concept of electric charge.
Another misconception has to do with the wires in a circuit.
I'll explain more after we take a short break. Okay,
(13:52):
so let's get another misconception out of the way. Many
people take that analogy of water pipes or hoses or
tubes as being a literal one to one with electricity,
and thus the wires in a circuit they think of
as empty conduits through which electrons can travel like. They're
(14:14):
imagining the wires as being these hollow tubes, and electrons
are just shooting down the tubes. They're coming out of
the battery or out of the wall if you have
something plugged in, shooting down the tube and getting to
the other end. But if we think about that for
even a moment, we realize that cannot possibly be true,
because the wires themselves are made up of atoms, and
(14:35):
atoms have electrons. So it's more like a tube or
a hose or whatever that is already packed with water
before you connected to the two pools. And even that
is not a perfect analogy. So let's talk about conductivity.
Some types of atoms have electrons in their outer energy
levels that are more lucy goosey. If you have a
(14:58):
single copper atom, then you've got a nucleus that contains
twenty nine protons and thirty five neutrons. Now we're talking
about a basic neutral copper atom, meaning the positive and
negative charges cancel each other out. So we have twenty
nine electrons paired up with that nucleus that has twenty
nine protons. Electrons orbit the nucleus, but not in the
(15:22):
same way that planets orbit stars or moons orbit planets.
The electrons inhabit various orbitals, which in turn are in
what we would call subshells, which are in shells around
the nucleus. Now I'm not going to dive into all
of that, because I'm sure most of you have a
general handle on it. But the twenty nine electrons and
copper add up to a point where one electron is
(15:46):
left orbiting the outermost shell. There's no room for that
last electron in any of the lower shells closer to
the nucleus, so this electron is pushed out to the
next lowest energy shell, and it's they're all by its lonesome.
That means that electron is easier to push around than
the ones that are locked in packed closer to the nucleus.
(16:11):
So when you lump a bunch of copper atoms together,
like that was just one copper atom, right, If we
put a bunch of copper atoms together and we've got
something like a copper wire that's made up of trillions
of these atoms, you end up with a mass of
copper atoms that all have these single free electrons, and
you can almost think of those electrons as moving around
(16:34):
the mass of copper atoms as opposed to being tied
down to a single copper nucleus. If you then connect
the wire into a circuit in which you have a
battery or some sort of generator or something, that battery
or generator acts as a pump that can push those
free electrons around. The negative terminal has a charge that
(16:56):
pushes against those electrons because remember like charge repels like,
so each of those electrons has its own negative charge
and pushes further down the path of the circuit. And
since since the other end of the battery has a
positive terminal, the negative charges get attracted to the positive side.
(17:17):
It's not that electrons are shooting out of a battery
down a pipe, doing some work, and then going into
the other end of the battery. Is that the charge
of the battery is pushing through this pathway and the
electrons carry that charge. Likewise, the electrons are not moving
at the speed of light. I know I've been guilty
(17:38):
of saying that before too, but that's not correct. The
electrons move much more slowly than the speed of light.
You could even say the charge moves more slowly than that.
But within the circuit, the charge is moving throughout all
parts of the circuit at the same time. It's not
like one electron moves and then the next one and
(17:59):
then the next one. It's like they're all moving together
in in lock step. And so you have this entire
circuit that all goes into motion at the same time.
And to us that means that we see practically instantaneous results.
So if you flip on a light switch to an
incandescent lamp, the light comes on immediately, it doesn't delay.
(18:21):
That's why. It's because all of those electrons in the
circuit are moving at the same time, so the effect
is that it's moving at the speed of light. But
in reality, what's actually happening is the electrons as a
whole in this circuit are all moving together. So a
battery connected to a circuit is not really a source
(18:41):
of electrons. It's a source of energy. It's providing the
energy or the pressure to move that charge through the circuit.
It's the source of voltage. An electrochemical reaction in the
battery acts as an internal circuit to create this voltage,
which manifests as a difference in electrical potential shold between
the positive and the negative terminals on the battery. Connecting
(19:04):
that battery to a circuit is what gives the energy
necessary to move this charge through the circuit and to
do whatever work it is you need to do along
the way, such as lighting up that light bulb. Within
a battery, you've got an exothermic reaction that is working
against the electric field. So it's kind of like pushing
(19:24):
a boulder uphill. The force of gravity in that case
would be working against you and you have to overcome it.
You have to exert effort to work against the force
of gravity to push the boulder up the hill. A
battery likewise is exerting effort in the form of this
exothermic reaction. The external circuit, that is, the larger circuit
(19:46):
that you connect to the battery, is following the natural
energy field. It isn't working uphill. It's got a high
potential terminal and a low potential terminal, and the current
flows according to the direct and of high to low
as Franklin described, The actual electrons are going in the
opposite direction. As the charge moves through the circuit, it
(20:08):
encounters energy transforming devices. These would be things like light bulbs,
heating elements, pretty much, you know, anything that you would
connect to a circuit. At those points, some of the
electrical potential energy of the charge gets transformed into some
other form of energy, light, heat, whatever. The loss of
electrical potential in a circuit after passing through one of
(20:30):
these elements is often called a voltage drop. Now going
to the water analogy again, imagine that you have a
pool of water. You have a ramp set up above
that pool of water, like maybe it's like a water slide,
and the water slide is not turned on, uh, and
it's smacked aub in the middle of the pool. You're
(20:51):
also in the middle of the pool, and you grab
a bucket and you fill it up with water from
the pool. You lift the bucket up over your head
to the top of the slide, and you tip the
bucket out so that the water hits the slide, goes
down the slide off the other end back into the pool. Well,
you've just taken water from an area of low potential
(21:13):
energy in this case, kinetic energy, and you moved it
using work to an area of high potential energy. The
water then flows down the ramp till it gets the end.
And maybe you even put a water wheel at the
base of this slide, so when the water hits the
water wheel, it actually provides the work necessary to turn
(21:35):
the wheel and you get the wheel turning. You have
this display of mechanical energy from the water. So that's
kind of what you would see with a battery in
a circuit. In this example, you are fulfilling the same
purpose of a battery. You are lifting some water using
(21:57):
work from an area of low potential to an area
of high potential. The battery is doing this but with
electrical potential, not with you know, physical stuff. Okay, now
it's time to define an actual vault. I alluded to
this in the first segment of this podcast. We've got voltage,
which is this difference in electrical potential between two points.
(22:21):
And we understand that creating a conductive path between an
area of high electrical potential and one of low electrical
potential allows for the flow of current. So how do
we define a vault. Well, there's actually a couple of ways.
One is to say that one volt is equivalent to
the energy consumption of one jewel per electric charge of
(22:42):
one coolomb. But that just raises more questions, doesn't it.
The dictionary definition of a jewel is a unit of
work or energy equal to the work done by a
force of one Newton acting through a distance of one meter,
and a Newton is a unit of force. One Newton
is the force required to impart an acceleration of one
(23:03):
meter per second per second to a mass of one
kim okay, So a jewel is the energy required to
produce a Newton's worth of force through a distance of
one meter. What's a coulomb. A coulomb is a unit
of electrical charge equal to the quantity of a current
of one ampier in one second. It's named after Charles
(23:26):
Augustine de Coulomb, who in the late seventeen hundreds developed
a description of the force that interacts between electrical charges.
He had determined that like charges repel each other and
that opposite charges attract each other, and his work led
to further discoveries that the force of this repulsion or
attraction is proportional to the products of the electrical charges
(23:49):
and inversely proportional to the square of the distance between
those two charges. And this is what we now call
Coulomb's law and another way to define volt That was
one way, but here's the other one. It's equivalent to
one amp of current times the resistance of one ohm.
And oh my goodness, looks like we're gonna have yet
(24:11):
another thing to talk about here. And while you might
hear that resistance is useless, I'm here to tell you
it's pretty important in the case of circuitry. So I
talked about how copper is a good conductor because of
those free electrons, right well, the single electrons in the
outermost energy shell around a copper nucleus make copper a
(24:31):
great conductor of electricity. We describe this quality of copper
as conductance, or the ease with which electrical current may
pass through that substance. The opposite quality is called electrical resistance,
the opposition of a material to the flow of current
through it, And typically we talk about that with materials
(24:53):
that have fewer or no free electrons, making it more
difficult for electricity to pass through. Even copper has some
electrical resistance. It's not a perfect conductor, at least not
under conditions you and I would typically experience. Resistance is
kind of like the concept of friction, right. We know
(25:15):
that an object in motion tends to stay in motion.
So if you were to roll a ball across a
perfectly level surface, and both the ball and that surface
were made of some magical material that ignored friction, there's
no friction in this system, then that ball would roll
forever unless it ran into something. But friction means that
(25:38):
some of the energy of that rolling ball in a
normal setting where we're using you know, a real ball
and a real level surface, friction means that some of
that energy gets converted into heat, and that means that
there's less energy for that ball to continue to roll,
and eventually the ball will slow down and stop rolling.
(26:00):
Electrical resistance is kind of similar to that typically we
see energy and electrical circuits convert into other forms like heat,
which dissipate into the environment at large. Now I mentioned
that one volt is equal to one amp of current
running through one ohm of resistance. Resistance then is the
(26:21):
ratio of voltage across whatever material we're talking about, divided
by the current going through that material. So resistance is
voltage divided by current, and conductance is the current running
through an object divided by the voltage across it, So
it's the reciprocal of resistance. Now we measure resistance in
(26:41):
oms and ohm is the amount of electrical resistance between
two points on a conductor when there's a constant potential
difference of one volt applied to those points, producing one
current or one amp here of current. I should say
electrical resistance depends on a lot of stuff. Depends upon
the atoms of the material itself, So the resistance of
(27:04):
a copper wire will be different than the resistance of
say a gold wire that's of the same thickness or gauge.
It also depends upon the thickness or gauge of a wire,
so a thicker copper cable will have less resistance than
a thin copper wire. And it depends upon stuff like temperature.
If you were to super cool some conductors, like get
(27:26):
it near absolute zero, they would then have them perform
as super conductors, which is material that can conduct current
with no conversion into other types of energy like heat.
You get no loss. In other words, likewise, there are
some materials that have tightly packed electrons that resist this
flow of current. I mentioned those earlier. We would call
(27:48):
these insulators. So materials that insulate don't allow for the
conduct conductivity of electricity or they severely restricted. Alright, so
quick rundown voltage is akin to pressure. It's the difference
in electrical potential between two points. Amperage is a measurement
of current and explains how much charge passes a given
(28:11):
point in a circuit within a unit of time. Ohms
are a measure of resistance, or how much material resists
the flow of charge through it. Now to define a what,
so a what is the amount of electrical work performed
when one ampere of current flows across one volt of
electrical potential difference? So what is a unit of power?
(28:33):
And this is where I find another stumbling block for myself,
because in language we often swap out words that have
similar meanings in other contexts, but very specific meanings in physics,
and it causes confusion for people like me. So words
like work, energy, power, and force they get thrown around
(28:55):
a lot, and it's easy to forget what they all
mean within the context of physics, and they mean different things.
A force is something that causes an object to change
its velocity in some way. Velocity is a vector quantity
that means it has both a magnitude and a direction.
So in our example of rolling a ball on a
(29:17):
flat surface, that ball would tend to stay in motion
at a constant speed and remain on a straight path
on its own unless some other force were to act
upon that ball and either speed it up or slow
it down, or make it change its direction, or some
combination of these things. That would be an external force
(29:41):
acting upon this system. You can think of energy as
the capacity for doing work, and it comes in lots
of different forms. A moving object has kinetic energy. For example,
work is a type of energy, specifically the amount of
energy used to apply some force on some object over
(30:03):
some distance. Now, as I mentioned earlier, the jewel is
a unit of energy defined as being equal to the
work done by a force of one newton across one
meter in the direction of action of that force. We
would describe the energy needed to lift a kilogram and
move it a meter in a specific direction as work.
(30:24):
Power is a description of the amount of energy used
per unit of time. So if you expend twelve jewels
of energy to do some sort of work, Let's say
it's to to move a wheelbarrow a few feet. Uh,
let's say that's that's how much energy you spent total
moving that wheelbarrow. This is a totally hypothetical example. So
(30:45):
you spent twelve jewels moving it. If you expended that
energy those twelve jewels over the course of three seconds,
your average output of power would be for watts. As
you take the twelve jewels that you took to actually
do this thing and the three seconds the amount of
time it took you to do it, and you divide
(31:06):
the twelve by the three, that's where you get the
four watts. When we come back, I'll talk a little
bit more about volts, amps, watts and how to read
your power bill. But first let's take another quick break.
(31:27):
I mentioned that one what is the same as one
jewel of energy expended in one second. So what does
it mean if your power bill is broken down by
kill a watt hours. Well, it's kind of simple, and
that a kill a watt hour is what it sounds like.
It's the equivalent to one kill a watt of power
(31:48):
sustained over the course of an hour of time. Since
and this is a unit of energy, right, Since since
one what is equivalent to a jewel per second? A
kill a lot hour is equal to three point six
mega jewels. Wait, how did I get that number? Well,
jewel per two. Right, there are sixty seconds in a
(32:10):
minute and sixty minutes in an hour, so we multiply
sixty by sixty to get us three thousand, six hundred
that's how many seconds there are in an hour. Then
we multiply that by one thousand because we have one
thousand watts because it's at kill a lot, So one
thousand watts times three thousand, six hundred seconds we get
three point six million. And remember a what is equivalent
(32:33):
to one jewel per second? That means a jewel is
equal to what's times seconds, So one thousand watts per
hour three pint six mega jewels are equal. We use
kill a wat hours to describe the amount of energy
used to do work. So let's say you've got an
appliance at home that requires a kill a lot in
order for it to do its work. So it's gonna
(32:53):
have a kill a lot of work in order to
do whatever it's doing. Let's say it's an air conditioner.
You gotta kill a what air conditioner. If you run
that appliance for one hour, it consumes one kilowatt hour
worth of energy to do that work. If you have
a ten what device plugged in, it would take that
device one hundred hours for it to use one kilowatt
(33:16):
hour of energy. Power companies usually sell electrical energy in
kilowatt hours, and it gets more confusing than that. Some
regions have varying prices on kilowatt hours. Sometimes that price
depends upon the time of day or the rate of consumption.
So we're just going to leave it at that. But
that's why we're talking about kilowatt hours as units, and
(33:38):
you're really thinking about this is the amount of energy
that is representative of doing a killer what worth of
work within an hour. I haven't talked about direct current
and alternating current yet, so I guess I should do that.
A bit direct current is what you would find in
a circuit connected to a battery. The direction of current
(33:58):
is always going to stay the same because the positive
and negative terminals on the battery are fixed. They can't swamp.
The positive terminal is always positive. The negative terminal is
always a drag guy. He's just always saying bad things
about everybody. Alternating current switches the terminals in a circuit,
and thus the direction of current switches back and forth,
(34:22):
and it does this in cycles per second. So in
Europe the standard is fifty times per second fifty cycles.
In the United States it's sixty cycles per second. The
reason we use alternating current is largely because of how
it's pretty easy to adjust voltages for the purposes of
power distribution. This is where things like resistance and voltage
(34:48):
and ambridge really become important. So let's say you've got
a power plant and that power plant produces one million
watts of power. But then you have to distribute that
power to the people who need it and the places
that need it. So how do you do that. Well,
you could send one million amps at an electrical potential
(35:09):
difference of one volt, because remember the watts are it's
really volts times amps. So if you have a million amps,
then your voltage has to be one or you could
send one amp very low current across an electrical potential
difference of a million volts. One amp would only need
(35:30):
a very thin wire. It doesn't need much wire at
all and would have very little energy loss due to heat.
A million amps would need an incredibly thick cable to
avoid losing too much energy to resistance or burning through
the wire entirely. And it would be very tricky to
come up with a method that works for both distributing
electricity across vast distances and also making use of that
(35:55):
electricity once it gets to the home. Like once you
get to the home, you don't probably want a super
high current in your home. It would burn out all
of your electrical appliances and probably kill you. Uh. You
also don't want super low current for like super super
low current, and you don't you know your voltage. You
(36:16):
don't need super high voltage for the home. So how
do you solve that problem? Well, direct current has issues
with that. Alternating current, however, allows for the use of transformers,
which lets you step up or step down the voltage.
Now I've talked about transformers in other episodes, so I'm
not going to go through all of that right now,
(36:38):
but they are how a power company can increase or
decrease the voltage. They can increase the voltage for the
purposes of transmission, where transmitting power at high voltage is
more efficient less power loss. You can push it further
distances and then step it down when it comes time
to distribute that power to read and so you step
(37:02):
it up for the purposes of transmission. It gets to
say a neighborhood, it goes to a different transformer that
steps the voltage back down a bit, and then that
transformers sends the power over to the households, where there's
another step down to get it down to the standard
in that house. So in the United States, that standard
(37:23):
is one volts, all right, So really it's to make
it more confusing, a pair of wires that combined offer
two hundred forty volts of power, but that's because of
alternating current. Most homes have an electrical service that provides
between a hundred to two hundred amps, though there are
exceptions both on the low end and the high end.
(37:44):
There's more I could go into with direct current versus
alternating current, including obviously the current wars between Westinghouse and Edison.
A lot of people say between Tesla and Edison, although
I think that's not entirely fair, uh, And I can
also talk about the equations used to describe direct current
versus alternating current. They are a bit different. But I'm
(38:05):
going to hold off on all of that for a
future episode because otherwise this episode would run way too
long for me to get into that. Something else I
did want to cover, however, was the difference between voltage
and amperage when it comes to safety risks. Now we've
established that these two factors are different. Voltage and ambridge
(38:26):
described different things. Voltage again, is that pressure and ambridge
is the amount of charge passing through a given point
in a given amount of time. But which is more dangerous?
Which one do you need to be more aware of? Well,
you've probably seen signs that say things like danger high
voltage when there's a fire at the disco or a
fire at the taco bell. Make sure you let me
(38:49):
know if you actually get that reference. It might just
be making a joke for my own sake at that point.
But is voltage the really dangerous factor here. Well, it's
a bit more complicated than that. Let's say you encounter
a current running at high voltage but very low ambridge,
so there's a lot of pressure in the line, but
(39:09):
not much electrical charge being moved through per second. That
would be less dangerous than a current a high current
with a relatively low voltage, So a high ambridge low
voltage would be more dangerous than a high voltage low ambridge,
And it doesn't take much amperage to do some damage
to us. When you get a zapp from an electrostatic charge,
(39:34):
chances are the brief current would have measured in the
one to ten milla amp range, So a mill hamp
is one of an amp. Less than that you probably
would even feel it, and one to ten you would
feel the little snap of an electric spark, but you
wouldn't have any muscular convulsion at that strength of ambridge.
(39:56):
Electro Static charges are are very high voltage but very
low ambridge. At about ten milli amps of current, you
would experience muscular contractions. If you grabbed hold of a
wire that had ten or more milla amps of current
running through that wire, you'd probably find yourself unable to
let go. As you got shocked, your muscles would clamp down.
(40:20):
At about twenty milla amps of current, you'd find it
difficult to breathe. If the current were around one hundred
miller amps, it would probably be fatal as it would
interfere with the operation of your heart. And it might
seem counterintuitive, but above two hundred milli amps you could
actually survive the experience. So between one and two hundred
(40:43):
is the real danger spot. Your heart would go into
uncoordinated contractions and you would experience was called ventricular fibrillation,
and that in fact can be fatal. Above two hundred
mill amps, your heart would actually seize up. It would
affect to really act as if it had been clamped down,
so it wouldn't go into ventricular fibrillation, it wouldn't have
(41:06):
those uncontrolled contractions. It would just stop. And if someone
were able to shut down the current going through you
fast enough, you could probably be revived. After that, you
could be given resuscitation and recover. You would probably have
some nasty burn injuries to deal with, and you would
probably also have some injuries and and damaged to your
(41:28):
internal organs. I have more to say about that in
an episode about the electric chair, where we did it
to people on purpose and continue to in some cases.
So that's the key there is that you really want
to be aware of the amperage and voltage is still important.
It's not like it's pleasant to get zapped by a
(41:50):
low amperage high voltage electric current, but it's not as
dangerous as the the amperage would be. And it's those
tiny little changes an amperage that will get you. So
be aware. Now I'll have to do more episodes to
talk about stuff like diodes, triodes, capacitors, and other components
(42:14):
in circuitry. I've covered them in previous episodes, but I
feel like taking this approach and really breaking it down.
Getting to the basics builds upon an understanding that we
can then rest more complicated subjects upon. Right, you can
start once you start understanding how these circuit pathways work
(42:35):
and what they do, and the behavior of electrical charge
and why that's important. Then you can build on that
and include things like quantum effects and why it gets
difficult when you start getting into concepts like logic gates
and quantum tunneling. You can you can touch on those subjects.
(42:57):
You can also understand what a logic gate is, and
you can understand how to build circuits to do actual,
you know, tasks like how you can create a circuit
to do calculations. But it all depends upon this basic
understanding of what is going on with these electrical charges.
And I find that if we start there we can
(43:21):
build a better understanding of everything else as we go along.
But that's gonna be for a later episode. Our next
one is going to be about using electricity to kill you.
I didn't. I did one on how people try to
use electricity to help you, and that continues to this
day to varying degrees of success in scientific rigor. And
then we're gonna talk about the other extreme in our
(43:44):
next episode, a pleasant topic to say the least, and
then after that we'll cover all sorts of stuff. I
haven't decided what goes on after that one, but if
you guys have suggestions for things I should cover in
future episodes of tech Stuff, you can reach out via
email The addresses tech Stuff at how stuff works dot com,
or you can reach out via social media. It's tech
(44:07):
Stuff hs W both on Facebook and on Twitter, and
go on over to our website. That's tech stuff podcast
dot com. You'll find a link to the archive of
all of our past episodes. You also find a link
to our online store, where every purchase you make goes
to help the show and we greatly appreciate it, and
I will talk to you again really soon. Text Stuff
(44:34):
is a production of I Heart Radio's How Stuff Works.
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