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EVERYTHING YOU EVER DIDN'T WANT TO KNOW ABOUT CHRISTMAS TREE LIGHTS AND WERE AFRAID TO ASK! |
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THE SIMPLE VERSION
How do Christmas tree lights work? You plug them in.
THE COMPLEX, LONG, IN-DEPTH VERSION
The process of making your christmas bulbs produce light starts in a ho hum, boringly simple story, so lets get through this first paragraph as quickly as possible, OK? Way far away, at your local power station, the energy stored in coal or in oil is being released through burning, transferring its energy to water molecules. Oh...you have a nuclear power plant? If you have a nuclear power plant supplying your power, the source of energy is a bit different. Neutrons, through nuclear fission of uranium atoms, procede from the busted atomic nuclei at speeds near that of light. As water captures the fast moving neutrons and absorbs the accompanying gamma radiation, it heats up. Regardless of source, the liquid water heats up and becomes transformed into steam, free-moving water molecules in the form of a gas. The speed of the steam particles is increased by constricting the water molecules...the same way the flow of liquid water in a garden hose can be increased with a nozzle. These super-fast steam particles, in turn, rotate a turbine which turns a coil of wire in a magnetic field, producing the initial push of electrons within wires connecting the power plant to your house.
For simplicity, I will bypass what happens to this flow of electrons at electric substations and transformers as they vibrate back and forth in the transfer of energy to the electric socket in your house. However coming from that socket, when you plug in the lights, is the energy which originated from the power plant.
What happens next leaves most people mired in the swamp of confusion because of some built-in ambiguities of the English language. I believe words became established to explain electrical phenomena before the perpetuators of those words understood the concepts of electricity. However, it adds some excitement to the story. At least it produces more Christmas confusion, and what is Christmas in America without some degree of confusion?
There is probably no topic in the entire field of physics, aye of science, with which the general public is more ignorant than that field of study we call ELECTRICITY. One of the main reasons for that is how the English language treats the subject. Consider the word "electricity" itself, not to mention other related words and phrases such as "charge" and "static electricity". These words are often misused not only in the publications of the national and local press, but even in science textbooks. Since most elementary school teachers do not hold degrees in electrical engineering, the misuse of these words often begins in the elementary classroom. The words associated with electromagnetic energy have been used in contradictory and misguiding ways.
The term "electricity" has no real meaning in physics. No single substance nor energy called "electricity" exists. We may talk about quantities of charged particles, electromagnetic energy, electrical potential, electomotive forces, electrical fields, net charge, electrical current, electrical power, or even about electrical phenomena. Yet, we shold handle the word "electricity" with extreme care. The layman, including the technology-ignorant press, uses the word much to often, and it is often used in contradictory ways. All of this has rendered its meaning vague at best and helped the English-speaking public to be ignorant of .....of.....of... ..well, of electricity. The layman often lumps the hundreds of terms physicists use to describe electrical phenomena into the definition of "electricity." The word, "electricity" should be limited to designate a specific field of science or class of phenomena, in the same way we use the word "astronomy." You don't go outside at night and say, "Let's look at the astronomy!"
Consider the confusion that the term, electricity, causes. In AC electric circuits, such as your Christmas light circuit, the charges oscillate at one tiny location in a wire, but the energy moves continuously forward. If the electic current and the energy it produces are both called "electricity", the message is that electricity sits vibrating in one spot within a wire while it simultaneously speeds down the wire at near the velocity of light! ARRRGGGHH! Let us just say that the vibrating charged particles, both positive and negative, sustain electromagnetic energy which moves down the path of the circuit. The electrons do their dance inside the wire, while the associated electromagnetic energy jets along the surface of the wire.
Electric phenomena show similarities to sound.
Air molecules vibrate and bump into each other transmitting sound energy
radially outward from the source, but the air particles themselves do not
move with the sound energy. As I have stated, there is no great wind produced
when I speak. (However, when I talk on this subject, I sometimes blow students
away!) Just as sound energy can propogate leaving the air particles,
through which they propagate, behind, electromagnetic energy can move at
speeds much greater than the charges through which this energy is transmitted.
As a matter of fact, charges within a wire can sit in place and simply wiggle,
yet the electomagnetic wave associated with that can move at incredible speeds.
(NOTE: Sound energy and electromagnetic energy have their differences, but
that is another story for another day!) It is, of course, contradictory to
say that "electricity" is vibrating in one spot while "electricity" is
moving down the wire, so lets not use that word! It would be more correct
to state that vibrating electric charges inside the wire sustain
electromagnetic energy to progress along the cylindrical surface of the wire.
OH YES, ABOUT THOSE CHRISTMAS LIGHTS: Your set of Christmas tree
lights is plugged into a wall, causing the bulbs to emit heat and light.
You are told in a pamphlet, magazine, or text book that "electricity"
enters each bulb, procedes through it, and then exits the bulb.
Once this is done, you read, the "electricity" turns around and does the
same thing in the opposite direction, repeating 60 times per second
(or 50 in some countries, i.e. Japan). Now here comes the kicker.
You read that in all of this in-and-out movement through the christmas bulb,
none of the electricity is used up! Yet,....GULP!....as you
read on, you "discover" that when the "electricity" flows from the
recepticle to the bulb, it is completely converted to heat and light!
Oh, the poor little brain of he that reads such as that! Is all the
"electricity "consumed by the bulb or does the "electricity" flow completely through it
unaltered? Certainly, it can not do both at the same time! Actually while
the charges vibrate in the wire, the negative electrons in one direction
while the positive part (the ionic metallic core) moves simultaneously in
the opposite direction, the electromagnetic energy which this act produces
is being converted to heat and light. (Yes, light, too, is a form of
electromagnetic energy, but its frequency is different from the original
frequency.)
DEEPER INTO CHRISTMAS BULBS AND THEIR CIRCUITS...as if you cared! To dive deeper into this idea of how christmas tree lights work, you must understand that all particles of matter have two properties: mass and charge. ALL particles! No exceptions! The electrons that wiggle have charge, but they also have mass. Within the copper wire, floating in the sea of electrons, are the stable inner cores of the copper atoms which for all practical purposes are positively charged copper ions made up of the positive copper nucleus and its inner electrons. This ionic core has even more mass than its free outer electrons, but since the metal is neutral, the amount of positive and negative charges are the same. In short the only differnce between the positive and negative moving-parts of the atom is mass. The positive mass is greater, but their charges are the same.
Electromagnetic energy is defined as the energy emitted from
vibrating charges, but heat is defined as the energy produced by vibrating
masses. Since both the electrons on the outer edge of the atoms and the
vibrating ionic cores pocess mass and charge, their vibration causes both
heat and electromagnetic energy. In a pure copper wire, the geometry of
the positive and negative charges is such that most of the electromagnetic
energy is caused by the freely moving electrons which have the same charge
as the ions but less mass, thus producing a higher electromagnetic-to-heat
ratio. However, the vibrating charges do have mass, so the copper wire must
become hotter. Probably the copper wire which connects the string of lights
does not heat up noticeably when current flows through it. It certainly does
not become so hot that it glows. In the filament of
each christmas bulb is a small wire whose atomic crystal
geometry is not as pure as copper. The charges within the bulb filament bounce
off each other like pinballs so that the energy that was once electromagnetic
from the vibrating charge, becomes heat, mostly a result of vibrating mass.
Too, if charge vibration is not uni-directional, the electromagnetic
waves start cancelling each other out. Not so with heat! There is no + or - mass.
If the atom arrangement in a wire is not orderly, collisions occur sending
particles with charge in all directions. This favors
the production of heat while diminishing the net electromagnetic energy moving along the
conductor. Regardless, the vibrating mass eventually establishes a resonant frequency, and since
the mass does have charge, when it gains enough heat energy, it starts
vibrating at the frequency of infrared and visible light...giving off both
heat and light to the observer. Why didn't the copper wire give off noticeable light and heat?
The copper wire connected to the christmas bulbs was made of a nice orderly
crystalline structure of atoms. The thin nichrome, tungsten, or whatever metal
happens to be in the christmas bulb was not blessed with this structure.
In metals, electric current is a flow of electrons. Within these metals, electrons flow incredibly slowly, at speeds on the order of centimeters per minute. It's the energy in the circuit, not the electrons, which flows fast. When the electrons at one point in the circuit are pushed, electrons in the entire circuit are forced to flow, instantly spreading energy througout the circuit. Energy and electrons are two distinct entities. Electrical energy is composed of electromagnetic fields which does not travel along with individual electrons. In the case of Christmas lights, this energy can be thought of as flowing through both wires from the plug in a tube-shaped geometry which then dives into the bulbs. Though caused by a movement of charges within the wires, this energy does not itself flow inside the wires.
If the same amount of electric current is flowing through a copper wire as is flowing through an aluminum wire of the same diameter, the charges in the copper will flow slower. Why, you should ask? Copper is a denser metal than aluminum. Since each metal atom has only one freely moveable electron, there are more atoms packed into the copper wire than into the aluminum one. Thus, there is more charge in each bit of copper. If you should tie a copper wire and aluminum wire in series so that the same current runs through both, when aluminum electrons flow into the copper, they get packed together and slow down. When electrons flow into into the aluminum, they have more room and accelerate. The speed of the charge, then, depends on the type of metal and the diameter of wire.
The formula to figure this out is
v = I / (q X e X pi X R^2 )
where
"Charge" can refers to several things: to the "net-charge" of an object,
to "quantities of charged particles" within an object, and to "charges"
of energy.
For example, even when
totally neutral, metals contain vast quantities of mobile electrons. So,
is it proper to say that they contain zero charge, or should we confess that
they contain huge quantities of charge? In truth, they contain emence
amounts of particles with charge, but the net charge is zero because there
are equal numbers of electrons and protons!
If I should place an electron and a proton together, do I have twice as much charge as before, or do I have a neutral hydrogen atom with no charge at all? Answer: There are twice as many charges but zero net charge because the negative charge of the electron in the Hydrogen atom and the positive charge of its proton cancel each other out.
Misuse of the word, "charge", makes accurate, clear descriptions of
electric circuits extremely confusing. Electric currents are a motion
of neutralized charge with negative charges moving in one direction while
positive charges simulaneously move in the other direction. Thus,
when we read that a wire is uncharged because it is neutral, yet current is
a flow of charge, we are bogged down in confusion.
How can anyone cope with a situation where a wire is uncharged yet
contains an enormous flow of charge? Wow, does that flow with confusion in a student's
ear!
Consider this example: if you charge a battery or capacitor,
you move charges from one terminal or plate to the other, and the device as
a intity has exactly the same charge before it was "charged". ARGHHH!
Speaking of "charging" capacitors or batteries is communicating about
energy. A "charged" battery has much more energy but exactly the same
net-charge, and exactly the same quantitity of particles as the dead
or "uncharged" battery. The concept of "charge" is very important in
understanding simple circuitry, yet the ambiguity of the term "charge"
impedes our understanding.
Well, I hope you got a charge out of that. Now that you understand the
multiple uses of the word, and you are all charged up, let us charge ahead!
For example, when scotch tape is placed on a table and then peeled off,
both the tape and the surface will become electrified. Place one piece of tape
on a table then another on top of it. quickly peel the tape off the table and then
quickly separate the two pieces of tape. See what happens! No friction was
required. Only contact. So why does your hair stand up when you comb it on a dry day?
Why does a dress ride up when rubbed against a stocking?
Why do you get a shock when sliding down a plastic slide with pants.
When at least one of the materials is fiberous, it does not give a very
large footprint of contact area. The process of rubbing the fibrous material
against the other can greatly increase the total contact area. For that matter, rubbing
any two materials together increases the contact area and thus the amount of
charge flow. However, do not be fooled! The rubbing is not the cause of
electrification!
Current electricity is not static either. Some people think that when a
circuit is broken and current ceases, we have static electricity. Sorry. WRONG!
And when an electric circuit is openned and the charges stop flowing, they
don't start attracting small objects or objects with opposite charge because the
conductors do not have a net positive or negative charge. Static and Current
electricity are two different electrical phenomena, but they are not opposite.
It is not so that one is moving charge and the other stationary charge. If
you should think that "static" and "current" are opposite types of
"electricity," you will never understand electricity
in general, and you will never understand how christmas lights work!
Just as important, electric current is a slow motion of charged particles within a conductor. Yet, Electric energy is made of fields and it moves fast outside of the conductor. Electric energy can move in a direction opposite to that of the electric current. The current running through a string of Christmas lights envolves alternating current where the migration of the electrical charges changes 60 times a second. Since the flow of the charges through the conductor is lethargic, the result is a group of charges that just wiggle in place. Even though the charges continually change direction, the electric energy moves continuously forward, clinging to the same wire where the direction of the current is alternating back and forth. Electric energy is composed of electric and magnetic fields which are perpendicular to each other, and it exists in the space surrounding the wires. The energy flows along both wires coming from the wall socket and dives into the bulbs, converting its energy into heat and light.
Electric current is very different than electromagnetic energy. Energy is not
made of stuff. It has no mass. For that matter, it has no charge. Electric
current is a flowing motion of electrons. Electrons are made of real stuff.
They are real particles with mass (1/1837 the mass of a proton) and charge
(the same charge as a proton). Thus, electric current is a flow of matter,
not of energy. I don't recommend this, but if you were to cut one of the wires
going to your christmas tree and place the two loose ends into a glass of
very salty water, the lights would still shine. There would be electric current.
When electric current exists in an electrolyte solution, such as salt water,
what flows is not electrons, but charged atoms called ions. Therefore, electric
current is a flow of material without a doubt; it is not an energy flow! The flow
of current through the wire enables the transfer of energy in the bulb.
Electric power, being a measurement of the flow of energy, has
no existance of its own. There is no power "stuff", so never talk about
the "flow of power" through the christmas bulbs. Electric power is an
energy current. In the metric system, Energy is measured in Joules. The rate of flow of energy is calculated
in "Joules per second", called Watts (named for the scientist, not the Christmas
song writer!) We can not measure Watts directly, because it has no real
existance. It is a calculated measurement. We measure energy and time
(Power is also difined as current X voltage, but that is
a story for another time.) "Watts" is a term of convenience. It is shorter
than saying joules per second.
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