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COME ON, WHAT IS ELECTRICITY, REALLY?
OK OK, enough with the definitions!
Here is the simple answer. There are TWO main things that flow along wires:
Because there are TWO things flowing, we cannot call them by the name "electricity." For this reason, we cannot ask "what is electricity?" Instead we have to ask more specific questions like these:
The answer to question #2 is ELECTRICAL ENERGY. It's also called
"electromagnetic energy". This energy is also like a "stuff" and it can
flow from place to place. It always flows very fast; almost at the speed
of light. It can be gained and lost from circuits, such as when a light
bulb changes the flow of electrical energy into a flow of light and
heat.
Here is a list of differences of these two kinds of "stuff":
Electric charge flows along wires. So does electromagnetic energy. If you ask "what is electricity", the answer is WHICH ONE? |
BACK TO FAQ
HOW DO WE MAKE ELECTRICITY?
How do we make electricity? This question is impossible to answer, since
the word "electricity" has no clear meaning.
OK, how about this. I'll answer the question, but I'll use the scientific
definition for the word "electricity." You probably won't like this,
since
most textbooks define electricity very differently than scientists
do. My answer is going to sound weird. Scientists say that electricity
is the quantity of electric charge.
School textbooks disagree; textbooks instead define electricity as the
quantity of electrical energy. But charge and energy are two completely
different things! For a list of the many differences between electric
charge and electric energy, see above.)
OK, forward to the answer!
"Electricity" means charge. Electricity is a fundamental property of
matter, so in order to create electricity, we have to create matter. The
positive and negative charges of electricity
are permanently attached to the electrons and protons in atoms. To make
electricity we'd have to create protons or create electrons! There is no
easy way to make electric charge out of thin air. It's not impossible
though. If you have a gigantic
particle accelerator at a physics laboratory then you can create new
charged particles. The same thing happens naturally in radioactive
materials and when cosmic rays from space strike atoms down here on earth.
But other than that, it's not possible to make any electricity.
If a textbook says that electric generators make electricity, that textbook is using the word "electricity" in an unscientific way.
But when the electric company says that they're selling electricity,
what's going on? Simple: they're using the unscientific definition of the
word "electricity." They really don't sell any electricity. Instead they
sell a pumping service. Instead they're just pumping electricity back and
forth inside the wires. That's what
"alternating current"
means. The electricity just sits in the wires and wiggles
60 times per second. The electric company sells a pumping service, and
you can use their service to run motors and heaters and light bulbs. They
sell
energy, but they don't sell you any electrons. The electrons don't even
really flow at all, they just vibrate.
Is this all too confusing? Maybe you'd like the answer to a different question: "HOW CAN WE MAKE ELECTRIC CURRENT?" See below. BACK TO FAQ
HOW DO WE MAKE CURRENTS OF ELECTRICITY?
All conductors contain some movable charges, some movable "electricity."
We never have to make electricity, since electricity is already there. We
just have to move it somehow.
So how can we move it? Just how can we pump the "electricity" and create
some electrical currents? Brief answer: CREATE VOLTAGE. Voltage is like
electrical pressure. To make a conductor's charges start moving, just
apply some voltage pressure across that conductor. There are three common ways to create voltages which can push electric charges along:
4. ANTENNA: Shine some radio waves on a short metal wire.(under construction)
BACK TO FAQ
WHAT IS "ALTERNATING CURRENT?" AND "DIRECT CURRENT?"
In an AC system, the wires are filled with vibrating charges. In a DC
system, the charges flow forward like a rubber belt. (And when everything
is turned off, the wires are STILL full of charges, but they aren't
flowing.)
Here is an analogy for understanding AC and DC. Get a bicycle wheel.
Fill it with mechanical energy by spinning it fast. Now put your finger
against the spinning tire. The tire slows down, and your finger gets hot!
The rubber tire acts like the charge inside the wires of an electric
circuit. It moves in a single direction, and that's what "Direct current"
means.
OK, now take the same bicycle wheel and have a friend start turning it
back and forth, back and forth. Have them do this very fast, so the
"turning" is more like a wiggling. Now put your thumb on the tire so the
tire rubs upon your skin. Your thumb gets hot! You have just
demonstrated "alternating current."
Your thumb represents an electric heater, while your friend was acting
like an "AC generator." The rubber bicycle tire represents the charges
flowing inside the wires of an electric circuit. We can pump them in a
single direction, and this creates "DC". Or we can use a different kind
of "pump", and force them to all move back and forth. This is "AC".
One last thing. It is very important that you realize that batteries and
generators do not create the flowing charges. ALL WIRES ARE FULL OF
CHARGES, all the time. All metals are full of movable charges. Batteries
and generators are "electricity pumps", but they don't create the stuff
that they pump. A circle of wires is like a wheel, and if you push its
charges along, then all the charges would move forward, just like the
rubber of a drive belt. We can only create an electric current if the
charges are already there. Fortunately, wires are full of movable
charges. They are like pipes which are always pre-filled with water.
BACK TO FAQ
ARE ELECTRIC CURRENTS ONLY ON THE SURFACE OF A WIRE?
In DC circuits and in 60Hz AC circuits, the current exists all through the
entire wire. The charge doesn't flow only on the surface. (If it did,
then we could replace all our expensive copper wires with cheap plastic...
just give the plastic a very thin copper coating.)
But the question brings up some important ideas. For example, when we
place an electrostatic charge on a wire, the charge spreads out and
occupies only the surface of the metal. It does not go inside. But this
makes no sense! After all, an electric current is a charge flow. If
charge exists only on the surface, how can electric current be deep inside
the metal? Yet currents really are deep inside, while electrostatic charge
appears on the surface.
Here's the solution... only *EXCESS CHARGE* exists on the surface of the
conductor, while electrons and protons themselves can be anywhere in the
metal. Remember that metal wires are already made of charge; they contain
a sea of movable electrons. This is always true, even when the metal is
uncharged. In other words, metals are always full of "uncharged charge"
because every movable negative electron is near a positive proton. The
negatives and positives cancel out. Yet still the "electron sea" can flow
along through the metal as if it were a kind of a liquid. The liquid is
made of charge, but it's cancelled-out charge; it's "uncharged" charge.
This flow is not on the surface.
But suppose we give the wires some EXCESS positive charge by removing some
electrons. This "excess charge" will migrate almost instantly to the
surface of the metal. It's all very confusing, no? The confusion occurs
because the word "charge" has two separate meanings. It means "a glob of
charged particles." Copper is full of movable electrons, so it is full of
"charge." But Charge also means net-charge, or negatives subtracted from
positives. Inside copper, the number of electrons and protons are equal,
so copper contains no "charge" at all. Yet copper is full of charge all
the time. It's all screwy! See my stuff about the word 'charge.'
These misconceptions make people argue over whether electric currents are
deep inside wires or only on the surface. Answer: they're deep inside,
yet wires can have a "surface charge," and this causes confusion.
To make matters EVEN MORE confusing, there is another phenomenon here
called...
THE SKIN EFFECT
The skin effect causes electric currents to avoid the middle of wires and
only appear on the surface. (GAH!!!!!!) But fortunately the Skin Effect
only applies to AC. Also, it's mostly significant for frequencies
far
higher than the 60Hz of household AC circuits. It's usually OK to ignore
the Skin
Effect unless you're involved with audio cables, antennas and
transmitters, electromagnetism theory, pulses and lightning strikes, etc.
The skin effect occurs because metals act as electromagnetic shields, and
because electrical energy always travels as electromagnetic (EM) fields
across circuits. When a generator sends electrical energy to your home,
the energy travels as EM fields near the wires, and the flowing energy is
solidly coupled to the electrons and protons in the metal wires. (Most
people assume that electrical energy travels INSIDE the wires. Not
so.)
When pulses of electrical energy travel along a wire, they produce an
excess charge on the surface of a wire, and they cause an electric current
inside the wire. But because the metal acts like an EM shield, at first
the path for electric current only exists on the surface. As the
millionths of seconds pass by, more and more electric current appears deep
inside the wire. Finally after a fraction of a second the current is
everywhere inside the wire. But what if we're dealing with Alternating
Current? Then the process has to re-start for every pulse of current.
If the frequency of the AC is low, then the current path has plenty of
time to migrate everywhere inside the wire. But if the wire is very thick
(many cm across,) or if the frequency is very high, then the current-path
never migrates very far from the surface before it has to reverse and
starts over.
Because of the Skin Effect, we can save money in high-frequency circuits
by replacing the expensive solid cables with cheaper hollow pipes. This
mostly applies to high-power radio transmitters. And with UHF and
microwave circuits, the "skin of current" is so thin that we can give the
copper conductors a plating of silver, and the entire current will exist
only in the high-conductivity silver... as if we were using all-silver
conductors. (In many circuits it would be best to use silver wires rather
than copper, but that stuff is too damn expensive.)
The Skin Effect also makes people argue over whether the currents are
inside the wires, or only on the surface. Answer: for DC and 60HZ AC
circuits, the skin effect can almost always be ignored. But the higher
the frequency, and the thicker the conductor, the worse the Skin Effect
becomes.
BACK TO FAQ
ELECTRONS FLOW SLOWLY, SO HOW CAN LIGHTS TURN ON INSTANTLY?
This question has an easy answer: the lights turn on instantly
because wires are ALREADY packed full of
movable electrons. So if the battery or generator tries to pull some
electrons out of one end of a wire, it has to suck all the electrons
forward.
Or, imagine a drive belt with two pulleys: when you turn one pulley, the
whole belt moves instantly, and the distant pulley turns too. Yet the
belt itself didn't move very fast. The electrons inside the wires are
like the circular drive belt. Here are other similar questions:
There's a big problem here. The word "electricity" is the problem.
Science books in elementary school correctly teach us
that electrons are particles of electricity, and that electric current is
a flow of electricity. In other words, they teach that electricity is
like that chain we
yanked upon. But then the books contradict themselves... they also tell
us
that electricity is... a form of
energy that travels almost instantly along the wires! WHAT?! In other
words, electricity the electrons themselves, and ALSO electricity is like
the wave that moved
along the chain of electrons? Well, which is it? If "electricity" is the
wave, it can't be the electrons in the chain.
The books are wrong. They're screwed up. Their authors don't understand
the difference between a wave and its medium. They don't understand
electricity at all. They teach that electricity is like
air flowing inside a
tube, but they ALSO teach us that electricity is like sound waves in a
tube. SOUND IS NOT AIR. No wonder we don't understand electricity. Yet
these authors are being paid to be the experts that our teachers rely
upon. In other words, our teachers don't understand electricity at all,
and it's because they trust books which are wrong.
I suspect that nobody wants to fix the books, since ALL these books have
the same mistake. To fix the error, first the book publishers would have
to be honest and take responsibility for such a huge problem. All the
teachers would have to admit that they're wrong. This hasn't happened
yet. Professional scientists have been complaining about this same
problem since the
1960s, and still it hasn't happened yet. But the internet lets us
expose the problem for all to see. See: The plague of errors in K-6 grade textbooksHere's a way to understand how electric circuits work. Get a long chain and hook its ends together to form a loop. Wrap this chain around two distant pulleys so the chain is like a conveyor belt. Now if you turn one pulley, what happens? The other pulley turns almost at the same time.
The chain is like the electrons inside a wire. The chain flows slowly in
a circle. That's how electrons flow too. However, energy flows very
fast. When you turn one pulley, the links of the chain yank on their
neighbors, and waves of energy flow down both halves of the chain. The
distant pulley turns almost instantly. And, (Ta Dah!) the first pulley is
like a DC generator, while the distant pulley is like a DC motor. The
circle of chain is like an electric circuit. The links of the chain are
like the electrons inside a wire.
BACK TO FAQ
WHICH IS MORE DANGEROUS, AC or DC?
NOTICE: I'M NOT AN EXPERT IN ELECTRICAL SAFETY. IF YOU NEED LEGAL
ADVICE, CONTACT A *GENUINE* EXPERT
Yes, DC batteries are fairly safe, but the wires within AC wall outlets are not. However, this has little to do with AC versus DC. Electric wall outlets would be dangerous even if they were DC. This danger is caused by two main things:
In the case of wall outlets versus batteries, it's the voltage of
the power supply that makes the difference.
Electric currents cause harm when the charges in your body are forced to
flow. Yet both
batteries and wall outlets can pump a large electric current. But it's
not their current-making ability that causes electrocution. Flashlight
batteries can put out several amperes, yet batteries are safe because
human skin is a relatively bad conductor. It
takes a fair amount of electric "pressure" (or voltage) in order to force
the charges within your body to start flowing. Touch both terminals of a
D-cell, and the electric current in your skin will be so tiny that you
can't feel anything. On the other hand, metal wires aren't like skin,
and it
only takes a tiny voltage to pump electric charge through a flashlight
bulb. Because the voltage of a D-cell is very low, it can only create
large currents in wires and in light bulbs, but not in people. OK, if 1.5 volts from batteries is safe, then what level of voltage is "dangerous?" The answer: it varies from person to person, but serious danger only appears when the voltage is higher than about 40 volts.The voltage of a typical battery is far below the 40 volts needed to electrocute you. AC wall outlets are 120V, which is far higher than the 40-volt threshold. 120 volts can force a large electric current through your skin, and therefore wall outlets are dangerous. The "AC" is not the problem, since an AC 12-volt power supply (such as the type used with laptop computers) is not dangerous, even though it is AC. The 12v computer supply DOES have the ability to produce large currents in wires, but its voltage is too low, and it can't produce a large current in a human body because the skin is too resistive.
Humans are electrically protected by their skin. Here's a disgusting
thought: remove your skin, and even a battery becomes a danger! If you
have a big cut in your chest, don't go sticking a 9-volt
battery into it. If you have huge cuts on your hands, then don't grab the
terminals of a car battery. It could stop your heart! (I guess it's
fortunate that most people don't stick electric wires into large open
chest wounds. Yeesh!) It's especially dangerous when the path for
current is
through your heart. If you have a big open wound on both your hands,
don't grab the terminals of a power supply, because the path for charges
would lead into one wound, through your arm, THROUGH YOUR CHEST, then out
through the other wound and back to the battery.
Flowing charge inside your body is dangerous, but it takes a voltage to
create a
charge-flow. A flashlight battery is probably not dangerous because the
1.5 volts can't create a large current in your heart. On the
other hand, high voltage by itself is not dangerous. For example,
if
you slide across a car seat and then climb out of the car, 20,000 volts
can
appear between your body and the car! Touch the car, and you feel a
painful spark, but you certainly aren't in danger of dying. High voltage
was present, but there weren't any continuous electric currents. You can
scuff your shoes on the rug and zap doorknobs all day with little harmful
effect, even though the voltage occasionally approaches 10,000 volts.
Everyday "static" sparks are not very dangerous, since the high voltage
instantly vanishes when the spark occurs, and it cannot produce a
large, continuing flow of charge through your body.
To be dangerous, an electrical energy
source needs to be above 40 volts so it can get through your skin.
Also the energy source needs to be able to
supply a large current for a long time (for at least a few
seconds.) OK, what about AC versus DC? What if the battery and the wall outlet both were 120 volts? Would one be safer than the other? Both can supply a large current, and both have dangerously high voltage. If we compare an AC high-voltage power supply with a DC supply of identical characteristics, here's one answer I've heard: All else being equal, AC is SOMEWHAT more dangerous than DC because AC has a slightly greater effect upon your heart.If an AC or a DC 120-volt power supply should shock you, and if the path for current should go across your chest, then the AC has a greater chance of triggering fibrillation and stopping your heart. Make no mistake, the 120V DC supply is nearly as painful and as dangerous. But if everything else is equal, a 60Hz AC high voltage cable is slightly more dangerous than a DC high voltage cable as far as your heart is concerned.
Another interesting tidbit: VERY HIGH VOLTAGE power supplies can actually
be less dangerous than the
medium-high voltage used in wall outlets. By "very high", I mean voltages
well over 500 volts. High voltage can be less dangerous because high
voltage can act as a natural heart-defibrillator. It re-starts your heart
at the same time as it stops your heart. High voltage also tends to
create
very high currents, which force your muscles to contract, which can throw
your body AWAY from the live conductors. If given the choice, I might
prefer to touch
a 1,000 volt wire than a 120 volt wire. With the 120 volts, my hands
would latch onto the wire and I wouldn't be able to let go. With the
1,000 volt wire there would be a big flash and a loud bang, and I could be
thrown across the room. (The energy didn't throw me, instead the current
made the muscles of my legs and arms do the work.)
On the other hand, very high voltage has its down side. It can rapidly
heat flesh and cause internal burns, whereas medium-high voltage would
take much longer to cause this sort of damage. In the above paragraph, I
might receive severe burns from touching that 1,000-volt wire, and maybe
loose a finger or hand, but I'd still be alive. (But if I grabbed tightly
to 1000 volts and couldn't let go, I'd quickly be roasted into charcoal.
No fun at all!)
BACK TO FAQ
WHICH IS MORE DANGEROUS, HIGH VOLTAGE OR HIGH CURRENT?
NOTICE: I'M NOT AN EXPERT IN ELECTRICAL SAFETY. IF YOU NEED LEGAL
ADVICE, CONTACT A *GENUINE* EXPERT
I remember arguing about this with other kids in elementary school. My
books and teachers were no help in answering it. Maybe this mystery is
one of things that attracted me to electronics in the first
place.
So, if I
answer your question and destroy the mystery, will you lose your
fascination with this field of science? (grin!)
People are harmed by electric current mostly because the current can stop
your
heart. High current can also cook your body or cause lethal chemical
changes in your muscles. But human skin is a poor
conductor. It takes a fairly high
voltage in order to push a fast flow of charges through a human body.
Voltage is like a "push". Voltage causes current. Voltage alone cannot
hurt you. However without high voltage,
electrocution could not occur. The voltage is the "pressure" that causes
charges in your body to flow along, and it takes more than about 40 volts
in order to push a big enough current through your body to severely shock
you.
High current is never dangerous as long as it remains contained inside a
wire. In order to cause problems, the path of the charge-flow must go
through your body and not just through a wire. A one-ampere current can
kill you, but suppose that 1-ampere current is inside a 3-volt flashlight
circuit? You can grab the bare flashlight wires without danger, and the
large current will stay within the metal. Three volts is too weak to push
a dangerous level of current through your skin. If the voltage of the
flashlight batteries were 120 volts, things would be different, and there
might be a dangerous current in your body if you grabbed the bare wires.
(Still, you'd have to grab them in such a way that your body became part
of the circuit.)
So, if a power supply is rated in volts and amps, which one is the
danger? BOTH. In order to be dangerous, the power supply voltage must
be higher than 40 volts, and the current rating must be higher than about
ten milliamps (1/100 ampere.) At a much lower current than this, even a
high voltage power supply cannot electrocute you. And if the power
supply voltage is well below 40V, it's not dangerous even if the current
rating is very high.
BACK TO FAQ
HOW CAN THE ELECTRONS FLOW SLOWLY, WHILE ELECTRICAL ENERGY FLOWS FAST?
Wires are always full of electrons (all metals are.) The electrons act
like a substance. Electrical energy is waves THAT travel through the
substance.
This topic is confusing because some books tell you that the electrons ARE
the electrical energy. Those books are simply wrong.
Here are some similar questions which might help to clarify things:
Electrical energy can move quickly along a column of electrons inside a
wire, even though the electrons themselves move slowly. ALL METALS ARE
ALWAYS FULL OF ELECTRONS. Wires are like pipes, but
these "pipes" are always filled with "water" all the time.
If something pushes the electrons forward into one end of a wire, all of
the electrons in the entire wire will try to move forwards, and energy
appears at the other end almost instantly. It's just like pushing on the
end of a stick: the whole stick moves forward, even if the stick is very
very long.
If you form the wire into a circle, then the electron-stuff in the
wire can act like a drive belt. If you force the electrons in the circle
of wire to move, ALL the electrons must flow in a circle (just like a
moving drive belt.) This is true even if the drive belt circle is miles
across.
So let's get back to our original question. The question is the same as this one: "HOW CAN A DRIVE BELT MOVE SLOWLY ACROSS THE PULLEYS, YET IT STILL DELIVERS MECHANICAL ENERGY ALMOST INSTANTLY FROM PULLEY TO PULLEY?" BACK TO FAQ
Why do electric outlets have three holes?
BACK TO FAQ
A BATTERY LIGHTS A BULB. WHAT'S GOING ON THERE?
BACK TO FAQ
WHY IS VOLTAGE NOT ELECTRICAL "PRESSURE?"
Voltage is "Potential", and potential is not pressure, even though a
potential-difference can "push" upon the electrical charges.
Here's one way to imagine it. Suppose we roll a boulder up a hill. This
stores potential energy, and we get the energy back if the boulder rolls
back down. Electrostatic fields are like gravity, and VOLTAGE IS LIKE THE
HEIGHT OF THE HILL. The higher we go, the more "gravitational potential"
we put into the boulder. But height is not pressure, and the hill is
still there even when the boulder is gone.
In a similar way, we need both voltage and charges before there can be any
"electrical pressure." The voltage only causes a "push" when the charges
are present. Voltage can appear in space, but if there are no charges,
then no pushing-force or "pressure" exists. This is very different than,
say, water pressure. Water can push on the surface of a submarine, but
the pressure doesn't go away when there's no submarine present. With
voltage, the "pressure" DOES go away, so voltage is not exactly like a
physical pressure.
Also see: What is "voltage?"
BACK TO FAQ
How are Watts different than Amps?
Amps and Watts are not the same, because
charge is not energy. Huh? It's because Amps are a measure of the
flow rate of charge, while Watts are a measure of the flow rate of energy.
Watts are a measure of energy flow, and a "watt" is just a
shorthand name for "Joules of energy per second." Keep in mind that Watts
are not like a stuff, watts do not flow, watts are a measurement of the
flow of something else: electrical energy. Joules of electrical energy
can flow along, and their rate of flow is called "Watts." If you have
twenty Joules of energy flowing in a circuit per second, then that's a
flow of twenty Joules/second, also called twenty Watts. (Maybe it would
be less confusing if we stopped using the word "watts" entirely, and just
said "joules per second" all the time.)
Amperes are a measure of charge flow, and an "amp" is just a
shorthand name for "Coulombs of charge flowing per second." Keep in mind
that Amps are not like a stuff, amps do not flow, amps are a measurement
of the flow of something else. Coulombs of charge can flow along inside
of wires, and their rate of flow is called "Amps." If you have twenty
Coulombs of charge flowing in a circuit per second, then that's a flow of
twenty Coulombs/second, also called twenty Amps. Another way to think about it: In power lines and in AC cords, "amps" are a wiggling flow, while "watts" are a one-way flow. The charge within an AC wire is 'alternating', or wiggling back and forth while sitting in place. The back-and-forth wiggling is measured in terms of amperes. On the other hand, electrical energy in an AC cord does not wiggle, and it does not sit in place. Instead it flows from the source to the load at almost the speed of light. This fast energy flow is measured in terms of Watts. Also see:
BACK TO FAQ What is Electric Charge? The simple, very brief answer: CHARGE is the stuff that flows during an electric current. CHARGE is not energy, instead it is a component of all everyday matter. All atoms are made of positive charges, negative charges, and a few other things. |
BACK TO FAQ
What's the difference between AC and DC?
This answer is about the letters "AC" and "DC". If you want to know
about
Alternating Current, see above
"AC" originally meant "Alternating Current", while D.C. meant "direct
current". Over the years the meanings have changed. AC has come
to mean "vibrating electrical signals." For example:
If you hear people talking about "AC voltage", you need to realize that they are not saying "alternating current voltage". Instead they are saying "vibrating voltage". BACK TO FAQ
How can we convert AC into DC, and vice versa?
To convert AC to DC, we can use an "electrical ratchet" which only allows
the charges to move in one direction. These "ratchets" are called Diodes
or Rectifiers. They act like a one-way valve for flowing charges in
wires. To change the vibrations of AC into one-way DC, just add a diode
to the circuit. Or, if
you need a device which takes in AC and spits out DC, then hook four
diodes together (this is called a "full wave bridge rectifier.) Converting DC to AC is more difficult. Some sort of "electrical wiggler" is required. The circuit is not simple, and must contain transistors or other types of electronic switching. This type of device is called a "DC to AC inverter." BACK TO FAQ
What happens during a "static" shock?
It's painful to get
"zapped" by the car door. What exactly is going on?
Most of the interesting phenomenon during a static shock cannot be seen
by humans: they're either invisible, or they're microscopic. First, the
imbalance of surface charges on a human body are totally invisible. No
matter how long you scuff your shoes on a rug, you cannot build up enough
charge to change your skin color! After all, your body is already made
of charge (made of protons and electrons,) and even the strongest surface
charge is just a teacup in the ocean when compared to the charge which is
already there.
Besides the invisible charges on your skin, the volume of space
around your body becomes filled by an invisible electric field. This is
where the electrical energy is stored. This field is very much like the
invisible field surrounding a magnet, but in this case it's an electric
field rather than a magnetic field. The field sprays outwards from your
entire body surface, then the flux-lines arc downwards to meet the floor.
They also bend around to meet the surface of any nearby metal objects
such as a car. The field concentrates itself on the pointy parts of your
body: fingers, elbows, ears, nose, the top of your head, etc. If the
floor is slightly conductive, or if you've been scuffing on the carpet,
then much of the field collects under your feet. The "field lines"
connect with the charges on your skin surface, and the other end of these
"lines" connect with opposite charges in the floor and surrounding
conductors. If there weren't any imbalanced charges in those other
surfaces, your charged body will create them by "induction," by pushing
away alike surface-charges while attracting opposite charges.
As you reach for a metal object such as a car door, the e-field becomes
concentrated at the ends of your fingers, and an intense patch of
opposite surface charge begins to gather on the car near your hand. The
total energy becomes slightly less as your hand approaches.
When your fingers are close enough to the door handle, a spark jumps. Or
in other words, the intense electric field in the space between your
fingers and the metal handle will tear the air molecules apart. First
the field stretches the molecules by attracting their alike charges while
repelling the unlike ones. Then finally an electron pulls loose from one
molecule. This electron takes off at extremely high speed, driven by the
e-field. It quickly strikes another air molecule, which liberates more
electrons, which then repeat the process. It resembles a landslide,
where one pebble strikes another, freeing it to strike others. This
"electron avalanche" glows violet, since some electrons are recaptured by
air molecules, and they emit violet light typical of ionized
nitrogen/oxygen mixtures. Some of the light is ultraviolet, and this
light knocks electrons off neighboring air molecules. Also, the region
of space that's filled with electrons and positive ions is a conductor, a
plasma, and so it distorts the flux lines of the electric field. Plasmas
typically take the shape of a long filament, a "lightning leader," since
the tip of the plasma filament is somewhat sharp, and it causes the
e-field to concentrate there (which promotes faster creation of plasma.)
The electron avalanche and the plasma filament can start out on the car
door, then reach outwards toward your fingers. Or it can start out on
your fingers and leap towards the door. Or it can be triggered by dust
motes in the space between the two, and then leap in both directions.
Charge polarity doesn't make too much difference, and the visible
"leaping" of sparks is NOT a motion of charges, it's not a visible
current. Instead it's an outbreak of glowing plasma, and this outbreak
can go in either direction.
Finally the plasma filament touches your finger and the car door. It's a
conductor with a typical resistance of a few tens of ohms. This
conductor EXPLODES. It has shorted out the capacitor plates formed by
your body
and the metal car. The e-field in the space between you and the car then
collapses inwards towards the spark. Electrical energy that was in the
space near your hand is flowing inwards towards the spark. (Energy
doesn't flow across the spark, instead the energy behaves like a cylinder
shape that surrounds the spark and shrinks inwards.)
A huge electric
current appears in
the spark, and temperatures in the air (and in the dead skin surrounding
your salty conductive flesh) rise to immense values. The air emits sound
and bright light, while your dead skin is cooked or even vaporized by the
electrical energy pouring into the spark. The pain you experience is not
necessarily electrical, it's similar to having your finger poked by a
white-hot needle. If you grasp a metal coin or some keys, and let the
spark jump to the metal, you'll feel almost nothing. The metal prevents
the burn while doing little to stop the current.
Painful finger-sparks can measure a few amperes, but they only last for a
hundredth of a microsecond. The worst ones can range up to many tens of
amperes, with peak energy flow up in the megawatts. But these sparks last
for incredibly brief times. Your nervous system
only responds on time scales of a tenth or a hundredth of a second.
Your nervous system "blurs" the energy and charge flows, and it "thinks"
that the wattage and current of the spark is roughly a million
times weaker than it actually is. Hurts though.
For more info about the typical "human finger sparks" used by manufacturers for
stress-testing new appliances, search for HBM or "Human Body Model":
Google: ESD, HBM, CDM, MM
ENGINEERING VERSION BELOW, some crude rule-of-thumb figures: A typical tiny spark, too small to see:
BACK TO FAQ
What is Static Electricity?
Static electricity is NOT electricity which is static or unmoving.
See Static Electricity
Misconceptions
Instead, "static electricity" is more properly known either as "High
Voltage" or "charge-imbalance." We could also call it "separated
electricity." Interesting things only happen whenever a large
amount
of positive charge is separated from a large amount of negative charge,
and it doesn't matter if the charges are moving.
It's the separation or imbalance which is important. The
stillness or static-ness of the charge has nothing to do with it.
To learn something about separated charge, see:
explaining electricity with colored plastic sheets.
Suppose you rub a balloon upon your arm. Hold it near your arm, and your
arm hair stands up. You probably don't realize that it requires around
100,000 volts to make your arm hair rise like that. Rubbing balloons upon
arms can easily create 100,000 volts or even more.
Also see: "Static"
actually means "high voltage"
"Static electricity" is NOT the opposite of electric current.
Suppose you have some "static electricity" on a wire, and suppose you use
a power supply to make
it flow along. What happens? You'll find that the wire still attracts
lint. It still can cause your hair stand on end. It still creates sparks
and crackling noises and purple corona discharges. In fact, all of the
usual "static" effects will
continue, even when the electricity starts flowing. But how can "static"
electricity flow along? It's not static anymore!! True, but remember,
"static" electricity is separated opposite charges. It's not electricity
which is static. As long as the positives are separated from the
negatives, all the usual electrostatic effects will continue.
Here's another way of saying it: flowing charges are
NOT the opposite of separated charges, so "static electricity" is not the
opposite of electric current. Or say it like this: voltage is not the
opposite of current, and we can have "static" and current in the
same circuit because the true name of "static" is Voltage.
Have you ever seen a Wimshurst machine or a VandeGraaff generator? Or a
Topler-Holtz device, or any of the other electrical
machines invented throughout the 1800s? Many people call these by the
name "static electric generators." This isn't correct. These machines
are meant to produce high voltage at low current. They are
mechanically-driven voltage
generators. If you study "static electricity", you are really studying
voltage itself.
Elementary school textbooks teach us that there are two different kinds of
electricity: "current" electricity and "static" electricity. This is
wrong. The textbooks are TRYING to teach a very important concept, but
the authors don't understand electricity enough to explain it. The real
concept is this: electricity has two main characteristics: the electric
current and the electric voltage.
Whenever you mess with "static electricity," you are actually playing with
pure voltage. "Static electricity" gives us some hands-on experience with
basic voltage concepts. But K-6 grade textbooks say nothing about this!
Instead they tell us that "static electricity" is unmoving charges. They
convince us that "static" is just obsolete Ben-franklinish stuff; ideas
which are only important for explaining dryer-cling and photocopiers. As
a result, we all learn something about electric current, but when it comes
to electric voltage we haven't the foggiest notion. So go take a look at "What is Voltage?" BACK TO FAQ
What voltage is considered "High Voltage?"
When someone says "high voltage," what do they mean? Is 120V high
voltage, or is it low? There's no SINGLE answer, since the answer depends
on the situation.
As far as human safety is concerned, "High voltage" is any voltage which
can injure or kill. Some safety organizations consider 60V to be
dangerous, and everything above 60V is called "high voltage." Others put
the threshold at 40V. If you soak your skin with salt water and then
solidly connect yourself to a DC circuit by grabbing some metal bars, you
can probably injure yourself with forty volts.
There is another meaning for "high voltage:" any voltage which can cause
sparks to jump through air. The tinyest sparks begin to be seen at
voltages between 500V and 700V, so anything above these values can be
considered as "high voltage."
There is another safety issue: at very high voltage levels you don't have
to touch the wires to be electrocuted, instead a flaming electric arc can
cross the air if you bring your hand too close. Significant sparks become
a problem
above voltages of several thousand volts. Electrical workers may consider
120V to be low voltage (and even 220V or 440V is often called low
voltage,) while the many thousands of volts in outdoor power lines is far
more lethal. It requires workers to use all sorts of safety procedures
when dealing with live circuits. In this case, "high voltage" is
something over 1000V or 2000V or so. Finally, there is so-called "static" electricity. To create tiny but visible sparks we need at least 1000V. To attract lint and to create painful "doorknob sparks" we need more than several thousand volts. To create hissing crackling noises and purple corona discharges from sharp points we need even higher voltages. In other words, "static electricity" involves High Voltage at tens of thousands of volts. Don't forget: a small tabletop VandeGraaff machine can easily generate 50,000 volts. Rubbing a balloon on your arm-hair can do the same. The larger classroom-style VDG machines can approach one million volts: high voltage by almost any definition. BACK TO FAQ
Do light bulbs consume huge energy when first turned on?
There is a myth going around which says we should leave our lights on all
the time. The myth says that, if we turn on our lights, this will consume
a huge amount of energy. But it's a myth.
You can prove this yourself. Go outside and find the electric utility
meter. See the little wheel which slowly turns? OK, now go indoors and
turn off everything in your house (including the furnace and water
heater.) Verify that the little wheel has stopped turning.
Next, turn on a single 100-watt light bulb in your house, then use a
wristwatch to time how long it takes the wheel to rotate once. This gives
you a rough idea of how much energy that light bulb is using every minute.
Now turn off the lamp.
Finally, have someone stand next to the lamp while you stay outside and
watch the electric meter. When you yell "start," have them turn on the
lamp, and at the same time start timing the little wheel. See how long it
takes the wheel to make one complete revolution when the bulb has
been suddenly turned on. (You timed the wheel earlier when the
bulb was already running normally, not when it was suddenly turned
on.)
You'll find that it doesn't matter much whether you turn on a bulb and run
it for a minute or so... or whether you simply leave the bulb on for the
same minute or so. The wheel in the energy meter gives about the same
mesurement in both instances, proving that light bulbs DON'T consume vast
amounts of energy when first turned on.
ON THE OTHER HAND, incandescent light bulbs tend to burn out when first turned on. The sudden heat will stretched their filament, and if the filament is about to break, turning it on can break it. So, if you leave the lights on all the time, you'll pay for wasted energy... but if you turn them on and off all the time, you'll shorten their lives. Which is more expensive? (If you want to get around this problem, then install "light dimmers" in place of your wall switches. This avoids the sudden stress of turn-on, and lets your incandescent bulbs last longer.) BACK TO FAQ
Why is Static Electricity invisible?
Whenever we create "static electricity" (more accurately called
"charge-imbalance"), the
imbalance of charge is very small. Compared to the amount of electric
charge already inside everyday
matter, the imbalance is too small to make a difference. Everyday objects contain many coulombs of cancelled-out charge in every cubic centimeter of their substance. You could create a visible change if you could add or remove a coulomb's worth of charge. However, a typical imbalance of charge is incredibly tiny. For example, rubbing a balloon upon your head involves millionths of millionths of coulombs (a decimal point with twelve zeros.) It's quite literally like a teaspoon of water added or subtracted from an ocean. Pouring a teaspoon of water into the ocean does not make the ocean look different. And if you rub a balloon on your hair, the surface of the balloon doesn't look any different. BACK TO FAQ
Why is electricity visible in sparks, but invisible when it's inside
the wires?
A spark is not electricity. A spark is NITROGEN/OXYGEN PLASMA. Plasma is related to fire. The plasma is created when some high voltage is present. High voltage causes air molecules to be torn apart, and as they hit other molecules or fall back together, they give off light. Plasma is conductive, so once it has formed between two wires, it joins the wires together electrically, and charges can flow through it. It might SEEM as if "electricity" has jumped through the air. In reality, a glowing "wire" has formed, and this "wire" is made of plasma. We can only see the plasma jump between the ends of the wires. We cannot see the flowing charges or the electrical energy. BACK TO FAQ What's the difference between static and current? BACK TO FAQ
Why does the electric company bill us, since it takes back all of the
electrons it gives us?
The electric company does NOT sell electrons. Instead, it only pumps
electrons. It pumps the movable electrons which fill the wires. The
electrons are provided by the atoms of the copper. You pay
for a pumping service!
Also, since power lines use AC, the electrons really don't move much at
all. Instead they sit in one place inside the wires and vibrate back and
forth. (It's somewhat like sound: the sound waves move fast, but
the air molecules just vibrate back and forth without flowing
forwards.)
Imagine this: if electric motors and generators had never been invented,
then the
"Power Company"
could use water instead.
The water would be inside a long, long loop of hose, and when the
"Hydricity Company" pumped the water, you could attach their hose to a
water
motor, and the motor would turn. The water inside the hose would serve as
a long drive belt. The water would stay inside the circle of hose,
and it would be pumped around the loop over and over again.
And when you opened the valve, your motor would turn on instantly,
even though the water might be flowing quite slowly. (When you
remove the blockage, the whole loop of water starts flowing at
once.) Many years ago, before motors and generators were invented, "power companies" used leather drive belts and rotating drive shafts to send energy to their customers. This really happened, although their customers were not way out in the suburbs. Instead their customers were all in the same area, and the "power company" was just a huge steam engine in the middle of a factory. Energy was sent to all of the factory machines using long leather belts and metal drive shafts. I guess you could say that these old factories ran on "Mechanicity" instead of "Electricity". Today we still use steam engines, although they're powered by nuclear reactors as well as coal or oil. Electric wires and electric motors aren't so incredible, they are really just a way to hide the leather belts that connect all the machines to the distant steam engine! BACK TO FAQ
When electricity is sent to homes, how does it 'know' if no appliances
are connected? Does it go back to the generators again?
Great question!
(And when you say 'electricity' I'll assume that
you mean electrical energy.)
Whenever the electric company sends electromagnetic energy to your
home, and when you don't have any appliances plugged in, something
interesting occurs. The energy bounces! It reflects from the open ends
of the wires and travels back to the big generators, where it's
automatically used to keep them spinning. Because this occurs, the
generators won't slow down much. And that means the
electric company won't have to burn much fuel at all to keep the giant
rotors going. But if you turn on all your lights and run all your
appliances, then some of the energy stops bouncing when it gets to your
house. The big generators start to
slow down, so more fuel must be burned to run the steam turbines which keeps
the rotors going at their original speed. Here is another way to say the same thing: If you unplug all of your appliances, less energy gets used.
Isn't this cool? I was fairly amazed to discover how electricity REALLY
works. I learned that the above question is not nearly as silly as most
educators believe. In truth, those big electric generators can reach out
through the wires and FEEL YOUR APPLIANCES. The generators "know" what's
connected. Whenever you plug in a light bulb, the electric company's
generators feel it almost instantlu. They feel the extra friction (the
electrical friction, not mechanical). Your light bulb uses up some
energy, and this means that some of the energy DOESN'T get reflected back
to the generators. As a result, the generators start to slow down a bit,
and more fuel must be burned in order to prevent this. By turning on a
light bulb, you can cause a distant nuclear reactor to eat more U-235, or
cause a coal-fired boiler to grind up a bit more coal into powder for
burning.
On the other hand, when you suddenly turn off a light, you create a "dead
end" in the energy system. The energy that was sent to your home starts
being reflected back to the big generators, and it makes them spin a tiny
bit faster. The electric company must then turn down the fires which run
the steam turbines to keep the generators from speeding up. They do this
quickly, and the changes in generator speed are extremely tiny.
BACK TO FAQ
HOW DO LIGHT BULBS LIGHT UP?
The filament inside a light bulb is much thinner than the wires that lead
up to the bulb. The charges flow slowly in thick wires, but they must
flow fast in the thin filament. Charges
experience a kind of "electrical friction", and when they flow faster,
more heat appears. This friction experienced by the fast charges heats
up the filament.
The same kind of "friction" heats up all wires, but the charges
flow slowly in thick wires, so this heating is usually not enough to
even notice.
The same kind of friction heats up the wires inside of toasters and
electric heaters. In that case, the heating isn't enough to make the
wires glow WHITE HOT like a light bulb filament. Instead they just
glow red or orange.
BACK TO FAQ
WHY CAN BIRDS LAND ON POWER LINES WITHOUT HARM?
The charges would rather go straight through the wire, rather than taking
a detour through the bird! Bird skin is a conductor, but copper has
thousands of times more conductivity. If a robot bird made of metal
landed on a power line, then there WOULD be charges flowing through the
metal bird.
BACK TO FAQ
WHY ARE HOUSEHOLD ELECTRIC OUTLETS AC? WHY NOT DC?
Two answers: wasted energy, and motor brush wear.
AC and DC are not that different. If
your
electric outlets were DC. then light bulbs and electric heaters would
still work fine. Many motors would still work. So what's the big deal?
DC motors require sliding brushes. Unfortunately,
carbon brushes wear out. If your fridge, fans and furnace contained DC
motors, you'd have to open them up about once a year to replace the worn
brushes. This would be even more inconvenient than replacing light bulbs.
But what if someone invented a special kind of motor which never needed
new brushes?
Nikola Tesla solved the problem by inventing the magnetic vortex
motor (commonly known as the AC Induction motor.) These motors have no
brushes to reverse the current. Instead they rotate because a magnetic
vortex pulls them along. However, these motors require AC. Their
operation is based on AC electrical waves. If you
never want to replace
motor brushes, then you need AC outlets to run all of your brushless
"Tesla motors."
Second answer: Nikola Tesla discovered how to make cross-country
electrical grids possible. If electric companies use AC, then there is
a simple
way to greatly reduce the electrical friction in every cross-country power
line. Just transport the energy at low current and extremely high
voltage. It's easy to change low-voltage AC into high voltage. Just use
a "transformer"; a pair of electromagnet coils.
But Transformers require AC. If DC was used, then either the
cross-country power lines would be too expensive (they'd have to be
immensely thick cables,) or the electric generators would have to be built
right in your neighborhood. With DC, cities would need thousands of small
generators instead of one huge generator at a dam or nuclear plant.
But WHY does AC make a difference? It's because electrical energy is made
of voltage and current, but only the current can waste energy by heating
up the cross-country power lines. If we could convert the energy into high
voltage and low current, then we could send it across hundreds of miles of
thin wire, and the electrical friction of the copper metal wouldn't absorb
all the energy. Unfortunately, electrical generators can't directly
produce a high enough voltage. However, there is a simple device which
can. It's called the AC Transformer, and it can convert low voltage
electrical energy into high voltage electrical energy. At the same time,
it converts high current into low current. If "transformers" are used on
both ends of a long power line, then that power line can be hundreds of
miles long, yet most of the electrical energy won't be absorbed by the
copper. But transformers only work on AC. They can't change the voltage
of DC. And so electric companies use Tesla's patents: low voltage
generators with transformers and high-voltage transmission lines.
If we had some other simple way of stepping the voltage and current up and
down, then maybe we could use DC instead. DC works fine for
running motors, heaters, and light bulbs. But if you want to send
electrical energy through very long wires, you need the AC so you
can convert it into high voltage at low current. (If the current
is low, then the long wires won't get hot, yet you still can send
just as much energy as when the voltage is low and the current is
high.)
Some people do use DC electrical outlets. Boats and campers
frequently have them. People living "off the grid", using solar or hydro
power, often use DC instead of AC. These people have nearby generators,
so they don't have to send energy through very long power lines. Some
appliances aren't compatible with both AC and DC, so anyone who has DC
outlets instead of AC outlets usually has to buy an entire set of DC-only
appliances. Also, some electric companies use DC cross-country power lines. They do this because high voltage DC has less energy loss than the equivalent AC energy. (You see, high voltage DC works better, it's just very hard to create it.) Electric companies use gigantic expensive transistor devices to convert DC into AC and AC into DC. They mostly use these specialized DC high voltage systems for very long cross-country transmission lines, and also to connect between statewide AC power grids. BACK TO FAQ
WHY DO BATTERIES GET "USED UP" AND "GO DEAD?"
Batteries are chemically-powered charge pumps. They contain "fuel" in the
form of chemicals (these chemicals are usually metals in the form of metal
plates.) When the chemical fuel becomes exhausted, the battery has "gone
dead". No chemicals ever leave the battery, so what happens to the fuel?
It turns into waste products.
If you have a rechargeable battery, then you can "recycle" the waste
products. By pumping charges backwards through the battery, you force the
chemical waste to turn back into fuel. This is a bit like pumping some
exhaust into your car engine, and having gasoline come out the other end!
The chemical reactions inside of rechargeable batteries are REVERSIBLE,
while the burning of gasoline is not.
BACK TO FAQ
THE LIQUID BETWEEN A BATTERY'S PLATES IS A GOOD CONDUCTOR, SO
WHY DOESN'T IT SHORT OUT THE BATTERY?
Batteries are chemically-powered charge pumps which create voltage. The
location of the charge pump is on the surface of the battery plates. All
batteries contain two charge pumps: one on each plate. These are
called the "
half-cell reaction sites."
In other words, even a single dry cell actually contains two separate
"cells." These cells are wired
in series, so their voltages add together. The surfaces of the metal
plates act as the true
energy-producing "batteries." The
conductive liquid acts as a wire. It connects these two
"batteries" together.
So, rather than being a short circuit, the conductive liquid is part of
the battery's internal "wiring," it's part of the complete circuit.
If you really wanted to "short out" the innards of a battery, you would
have to somehow di
srupt the thin surface layers of the battery plates.
If part of those layers were destroyed, this would let the charges on one
side of the
charge-pump go directly to the other side without having to flow through
the
battery's outside terminals. (And this is one reason that batteries have
a
"shelf life;" it's because part of the battery plates stop acting like
charge pumps, and in that case some charge does leak backwards across the
pump, causing the battery to eventually go dead. )
BACK TO FAQ
WHAT IS THIS "COMPLETE CIRCUIT" STUFF ABOUT?
In order for charges to flow continuously, they must be within a circular
path.
Why? Because all wires are full of charge, and the charge cannot leave
the metal. If you want to push more charge into one end of a wire, the
charge at the other end must have some conductive material to go into.
Connect a wire
in a circle, and the charge within the wire is able to flow anywhere
within the circle. A circle of wire contains a sort of "drive belt" made
out of electric charges.
An "open circuit" has a blockage made of empty space, while a "closed
circuit" has a complete circular metal path with no blockages.
If you break the circuit, this is the same as grabbing the drive-belt so
it cannot move. For electric circuits to operate, the "electron
drive-belt" inside the wires must form a complete circle with no air-gaps
to "put on the brakes" and halt the motion of the invisible "belt."
BACK TO FAQ
WHY DON'T AC MOTORS WIGGLE BACK AND FORTH? WHY DO THEY RUN FORWARD, WHEN
THE CHARGES IN THE WIRES JUST WIGGLE?
This was Nikola Tesla's great invention: to use the vibrations of
Alternating Current
to create a rotating magnetic vortex, then let the magnetic vortex cause a
hunk of metal to turn. The rotating magnetic field sweeps through the
metal and drags it along. These are called "induction motors."
There's also another way to do it. Suppose we take a little battery
powered motor and remove the magnets. Replace them with electromagnet
coils. Connect the coils (and the motor's rotor) to AC. Now whenever the
current reverses, all of the magnetic poles in the motor reverse too, and
the motor still spins in the same direction. The
"N" attracts the "S", but when the current reverses direction, the "S" now
attracts the "N", and the motor still turns the same. If you feed AC to
that motor, it will keep spinning even though the direction of current is
flipping back and forth.
BACK TO FAQ
WHAT'S THE DIFFERENCE BETWEEN BIG AND SMALL BATTERIES?
In the USA, the"D" cells, "C" cells", "AA" cells, and "AAA" cells are
almost the same except for the amount of chemicals that they contain. The
bigger batteries just last longer. Otherwise they are exactly the same
9-volt batteries are different. If we break open a 9-volt battery, we'll
find six little 1.5-volt batteries inside of it. The same is true of
6-volt lantern batteries. Open up a 6-volt battery, and you'll find four
1.5-volt batteries inside.
BACK TO FAQ WHY MUST BATTERIES BE INSERTED IN THE "RIGHT DIRECTION?" BACK TO FAQ
WHAT'S THE DIFFERENCE BETWEEN "POWER" AND "ENERGY?"
"Energy" is a stuff that flows, while "power" is the rate of energy flow. If
"energy" were like water, then "power" would be the gallons per second.
BACK TO FAQ
WHY CAN'T BATTERIES ELECTROCUTE PEOPLE?
They can! But you'd need lots of batteries. Single electric cells are
very safe.
Everyday batteries are safe because their voltage is so low.
First, understand that electrocution is not just caused by electric
current. Instead it
is caused by an electric current inside your body. Currents
themselves are
not dangerous as long as the path for current is through a wire! Voltage
is important here, but voltage is not dangerous unless it causes a current
INSIDE your body.
Human skin is electrically conductive, but it is not a good conductor.
It takes about 40 volts of electrical "pressure" in order to create a
dangerous electric current inside your flesh. 40 volts is the "danger
voltage." Anything higher than 40V can shock you. Fortunately, most
batteries are way below 40 volts (most are below 12 volts.) Batteries
lack the pumping-force needed to create dangerous currents in humans.
Another way to say it: our skin is insulating enough to keep us safe from
batteries, but it cannot protect us against the high voltage of a 120V AC
outlet.
Batteries CAN electrocute people if you connect a large number of
batteries in series. Put a hundred D-cells in series, and that gives you
150 volts, which is more than enough to kill you if you touch the wrong
wires.
Batteries CAN electrocute people if the path of the current somehow goes
through your skin. For example, if you made some big bloody cuts in your
hands, then even a 6V flashlight battery might kill you if you placed
those cuts against the battery terminals.
And if people were made of metal, then even a single D-cell would be
dangerous!
BACK TO FAQ
WHY ARE TWO WIRES NEEDED?
I will answer this question with a question. When a circular belt is
passing over two pulleys, why are two belts needed? The answer: THERE ARE
NOT TWO BELTS! There is only one belt, and the belt is circular. It
looks like there are two belts, with one of them flowing leftwards and the
other one flowing right. But in truth, there is just one belt, and it is
rotating.
So, why are two wires needed? The answer: THERE ARE NOT TWO WIRES!
Instead there is only one wire, but it is connected in a circle. All
metals are full of movable electrons, so when we connect a wire in a
circle, we are forming a kind of "electric drive-belt" which can move
inside the wire. But household electric outlets have THREE prongs! Yes, but only two of them are used. The third one is only used for safety purposes. See WHY THREE PRONGS BACK TO FAQ
WHAT'S THE DIFFERENCE BETWEEN VOLTAGE AND CURRENT?
Voltage is sort of like electrical pressure.
A current is a flow of electric charge.
It's best to think of it like this: voltage CAUSES electric current, just
like water pressure causes water to flow.
You can have a voltage without a current: when a battery is sitting on a
shelf, it is creating a voltage between its terminals, but there is no
current. It's like a force without a motion. It's like a pressurized
balloon, but without any leaks.
You can also have a current without a voltage: a ring of 'Superconductor'
can contain a loop of flowing charge that flows inside it forever.
It's like frictionless motion (with no force needed to keep it going.)
It's like a flywheel which keeps spinning forever.
Voltage is associated with electrostatic fields in space. Whenever you
have a voltage, you also have an electric field.
Current is associated with magnetic fields in space. Whenever you have an
electric current, you also have a magnetic field.
Also see:
BACK TO FAQ
WHAT IS ELECTRICAL ENERGY? WHAT DOES IT HAVE TO DO WITH VOLTAGE AND
CURRENT?
Ooooo, good question! It ties in with "what is charge" and "what is
electricity"
Here's the very briefest answer: Electrical energy (also called
electromagnetic energy) is made of electric fields, and also is
made of magnetic fields. If you have a bar magnet, the invisible
"stuff" that surrounds the magnet is the electrical energy. If you have a
charged balloon, the invisible "stuff" that surrounds the balloon is the
electrical energy. If you have an electric circuit, the energy can be
found in the invisible fields that surround the wires. Electrical energy
has two faces: magnetism and "electricism" (magnetic fields and
electrostatic fields.)
Where do voltage and current come in? Easy: the voltage is part of
electric
fields, and the current is part of magnetic fields. For example, when you
have a flow of charges in a coil of wire, a magnetic field appears around
the coil, and energy is stored in the magnetic field. Even if the wire is
not wound into a coil, there is still a magnetic field surrounding the
electric current in the wire. We could almost say that electric current
IS the energy, since whenever a current exists, there MUST be a magnetic
field and there MUST be energy present in that field. (Almost, but not
quite, since the energy is in the fields and not in the flowing charges.)
In a similar way, voltage is profoundly connected with electric fields.
When we "charge" up a capacitor, energy is stored in the electrostatic
field between the capacitor plates. Even if no plates are present, the
wires of an electric circuit will act like capacitor plates, and energy
will be stored in the voltage-fields that surround the wires. If we have
voltage, then we MUST have an e-field, so we MUST have some electrical
energy present.
When a battery powers a light bulb, where is the energy flowing? Does it
flow inside the wires where the current is located? Nope. It flows in
the space
outside the wires. Here's a way to think about it:
Electrons and protons are not particles of energy (they are matter.)Can generators really make radio waves? Yep. However, in order to get the waves out into space, the antenna needs to be about the same size as the waves. At sixty cycles per second, you'd need an antenna that was many hundreds of miles long. At the turn of the century, radio pioneers actually used AC generators to create radio waves. They called these "alternators", and they ran at extremely high frequencies. Since electrical energy is electromagnetic fields, and since electromagnetic fields are the same "stuff" as radio waves, it makes sense that the energy in electric circuits can also fly through empty space all by itself.
BACK TO FAQ
COULD ELECTRICITY WORK WITH JUST ONE WIRE?
Amazingly, the answer is yes. However, this can only be done with AC and
not with DC. Also, the frequency of the AC must be very high, much higher
than 60Hz. If we want to send electrical energy using one wire, then rather than using a single straight wire, instead we must use a very long hollow coil (like wrapping a single wire around a very long rod.) Nikola Tesla invented this single-wire energy transmission scheme. It uses standing waves to transmit energy from one end to the other. Amazingly enough, NO COMPLETE CIRCUIT IS NEEDED. The coil acts a bit like an organ-pipe, but the waves are not sound waves, they are electromagnetism. If a generator is connected in series with this coil, and a light bulb is connected in series too, then the generator can light the bulb. His invention played a big role in the early development of radio, but it was never used for commercial energy distribution. BACK TO FAQ
Why doesn't the incoming electricity run out onto the carpet or
something?
Once I thought that this was a silly question. Today I realize that it is
a very sensible one. It exposes some profound aspects of electricity.
People who ask this question are on the right track.
Wires are full of movable charges, and when these charges are moving, we
call this an "electric current." What keeps the charges inside the wires?
Why don't the charges just fly out into the air?
The answer is: static electricity!
Wires, as well as everything else,
contain an equal amount of positive and negative charge. If we try to
take some charges out of the wire, the negative attracts the positive, and
the charges are pulled back inside. It takes a lot of work to pull
charges out of a wire, and this doesn't just happen by itself.
Pushing charges out of a wire requires a very strong push; it requires
high voltage. 120volts is far
too little to do this, but it can be done with 10,000 volts. If
electrical outlets used 10,000 volts instead of just 120V, charges would
constantly leak out of the wires and be pushed right out into the air! If
you stood too close to 10,000V wires for too long a time, you might begin
to feel some "static cling" on your clothes. No lie! The charges in the
wires will spew out into the air.
On the other hand, even 10,000V can't push much charge out of the wires.
For example, to remove all the free electrons from a piece of #18 lamp
cord and place them in the ground a few feet away reqires REALLY high
voltage: approximately 1,000,000,000,000,000,000 volts (10^18 V)
So that's why electricity remains trapped inside the wires: the electrons
and protons in the metal are being pulled together quite strongly. A
metal wire is like a tank of water: the water can easily swirl around,
but it can't leave the tank. A metal wire is like a river in a deep
canyon, and the water cannot leave because the walls of the canyon are
millions of miles tall.
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