Post by organist89 on Feb 17, 2007 20:31:26 GMT -5
Well, I've always been interested in the evolution of electricity and electrical devices. In addition, I'm a U.S. history enthusiast; so, I combine both of those passions when I do research about the timeline of lighting in this country.
With events which one did not directly witness (i.e. things that happened before we were born), we learn about them through the retellings of others. And as is the condition of the human to be subjective, certain facts are left out while others are emphasized, some stories are exaggerated or emboldened, and things tend to become distorted with time. A very good example are the school textbooks which teach that Christopher Columbus sailed in 1492 and landed in what is now the USA and asked the indians to move back so he could set up camp. In reality, he landed in what are the present-day Bahama islands, committed the complete genocide of the entire Arawak indian race (he and his men would often behead children and eviscerate pregnant women "for sport"), and raided all the villages for their gold. But no, the school textbooks speak only of heroic adventures--and we even go so far as to celebrate him with a day in his honor; this is why i do NOT celebrate Columbus Day.
For anyone else who's interested in U.S. history and wants to hear a different, more clear and historically accurate (albeit upsetting) account of this country's past, check out "A People's History of the United States 1492 - Present" by Howard Zinn. It was the textbook we used for my 11th grade history class, and WOW was it an eye-opener.
Anyhow, another person from our history who is constantly being canonized (turned into a saint) is Thomas Edison. We think of him as a quirky old fellow who loved solving puzzles and so ended up inventing things such as the light bulb and phonograph. And while he did invent the incandescent light bulb (arc lighting existed previously), and contribute many other great things to science, he also did some rather evil things.
One such deed was related to his bitter rivalry with Nicola Tesla. Edison wanted to be the most famous inventor of all time, and he wanted ALL of his ideas put to use, and not used in conjunction with anyone else's inventions. Now, back in New York City in the latter part of the 19th century, electrical generators were being built and wires being installed so that a few places--colleges, and the homes of the very rich--could benefit from the invention of the light bulb.
Edison, brilliant mind that he had, perfected the DC (direct current) generator. He thought DC was the way to go. Dear darling Mr. Tesla, on the other hand, was a big proponent of AC (alternating current), and he was making proposals to the city to install AC generators instead. And that made Edison furious.
DC works by sending a steady stream of electrons through a wire; they then flow out into the earth or dissipate into surrounding objects (this is referred to as "becoming grounded"). In the case of a motor, these electrons pass through a coil of wire which surrounds a permanent magnet (as opposed to an electromagnet). By the laws of physics, DC electricity produces a magnetic field. Magnetic fields are bipolar--they have two equal and opposing forces, which we refer to as the North and South poles. In a DC motor, electrons start flowing from one side and flow through the circuit (in this case a coil of wire) to the other side. As they being their flow, they create a magnetic field which repels the permanent magnet towards the other side of the coil--so, the magnet begins to turn. When it reaches the horizontal point (where it would naturally stop and hover between the opposing magnetic forces coming from the two sides of the coil), a bit called the "commutator" flips the polarity of the magnetic field (gives the power to the side the magnet has moved towards), and the magnet is once again repelled--so, it continues turning. And so it is an endless loop, until the current is interrupted (the motor is switched off). Interestingly, a DC motor and a DC generator are essentially the exact same thing. If you shut off the power and turn the magnet by hand, you induce an electric current in the wire coil surrounding the magnet. Cool, eh? Anyhow, without a commutator, DC current does nothing in a motor. The current just flows through and out into the ground, rendering no force. It's harmless.
AC, on the other hand, works by acting as the commutator. You know how, in this country, we have "60 Hz" (hertz) current? What that means is that the current switches polarity 60 times per second. In an AC setup, there are three wires which come into your house: 2 load ("hot") and 1 neutral. One of those load wires is +110 volts, and other is -110 volts. 120 times every second, the power is switched from the +110 load to the -110 load (hence each is activated 60 times every second, hence 60 complete "cycles per second", hence 60 Hz)--this is graphically represented as a sinusoidal waveform. When speaking in terms of a motor, this force acts as the commutator. The +110 volts creates an electromagnetic force in the stator, which starts the rotor in motion. When the power "alternates" to the -110 volts, the opposite force ("pole", in DC terms) occurs and sends the rotor through the other half of its cycle. Speaking in terms of current flow, this is the fundamental difference between AC and DC: DC sends a constant current through a wire, where it either has an effect or doesn't, depending on what's in the circuit. AC doesn't actually send any electrons through a wire--it just rapidly polarizes and re-polarizes the free electrons which are already present in the conductor.
Speaking in simple terms, DC is not dangerous. You can touch a DC circuit and not be shocked--for example, if you touch a battery. When you touch both sides of a battery or other DC power source, current flows through you. Since you don't have a commutator inside, nothing happens. The current just flows harmlessly through one arm and out the other. AC, on the other hand, is extremely dangerous. Since it acts as the commutator, it attempts to turn you into a motor. If you touch both sides of an AC circuit--for example, if you stick your finger in a light socket, the current takes the free electrons in your body (because you're a conductor) and rapidly polarizes and re-polarizes them. You experience this as a painful shock. Also, since your heartbeat is controlled by electrical impulses, the AC current turns your heart into a polarized motor; this usually results in a nasty consequence such as death.
One of the most outstanding advantages that AC has over DC is its ability to travel long distances. AC can have its voltage changed, and then be sent over long distances from the power company to your house. DC, on the other hand, works on a scale of exponential decrease. The farther you send DC, the weaker it gets, and this force is pretty dramatic--to the point that we'd literally need a power company every few miles along each road.
So, back to the late 1800's.
Edison was a pig-head, and wanted DC used despite its obvious disadvantages, because HE, the great Edison, had perfected it. Tesla was pushing AC because it was more efficient.
So Edison went for the manipulation tactic--here comes his evil deed. He decided to appeal to the public fear of this new-fangled force called electricity. He would go down to the city pound and get a dog or cat, and then he'd go buy an old show elephant from a circus that had no more use for it. Then he'd hold an expo in downtown Manhattan where he'd hook the cat/dog up to DC and it would be fine; then, he'd hook the elephant up to AC and it would fry like a guy in an electric chair. This violently graphic (needless to say cruel) display was his method of pushing his DC theories. Anyhow, as history as shown, he lost the battle with Tesla.
The most common complaint about AC relates to fluorescent lighting and CRT computer screens--some people are very sensitive to the 60 Hz flickering. In the case of a computer monitor, you can set your refresh rate higher--85 Hz works for almost all folks. But you can't do that with a fluorescent light, so some people get headaches after a long day in a fluorescently-lit building.
With events which one did not directly witness (i.e. things that happened before we were born), we learn about them through the retellings of others. And as is the condition of the human to be subjective, certain facts are left out while others are emphasized, some stories are exaggerated or emboldened, and things tend to become distorted with time. A very good example are the school textbooks which teach that Christopher Columbus sailed in 1492 and landed in what is now the USA and asked the indians to move back so he could set up camp. In reality, he landed in what are the present-day Bahama islands, committed the complete genocide of the entire Arawak indian race (he and his men would often behead children and eviscerate pregnant women "for sport"), and raided all the villages for their gold. But no, the school textbooks speak only of heroic adventures--and we even go so far as to celebrate him with a day in his honor; this is why i do NOT celebrate Columbus Day.
For anyone else who's interested in U.S. history and wants to hear a different, more clear and historically accurate (albeit upsetting) account of this country's past, check out "A People's History of the United States 1492 - Present" by Howard Zinn. It was the textbook we used for my 11th grade history class, and WOW was it an eye-opener.
Anyhow, another person from our history who is constantly being canonized (turned into a saint) is Thomas Edison. We think of him as a quirky old fellow who loved solving puzzles and so ended up inventing things such as the light bulb and phonograph. And while he did invent the incandescent light bulb (arc lighting existed previously), and contribute many other great things to science, he also did some rather evil things.
One such deed was related to his bitter rivalry with Nicola Tesla. Edison wanted to be the most famous inventor of all time, and he wanted ALL of his ideas put to use, and not used in conjunction with anyone else's inventions. Now, back in New York City in the latter part of the 19th century, electrical generators were being built and wires being installed so that a few places--colleges, and the homes of the very rich--could benefit from the invention of the light bulb.
Edison, brilliant mind that he had, perfected the DC (direct current) generator. He thought DC was the way to go. Dear darling Mr. Tesla, on the other hand, was a big proponent of AC (alternating current), and he was making proposals to the city to install AC generators instead. And that made Edison furious.
DC works by sending a steady stream of electrons through a wire; they then flow out into the earth or dissipate into surrounding objects (this is referred to as "becoming grounded"). In the case of a motor, these electrons pass through a coil of wire which surrounds a permanent magnet (as opposed to an electromagnet). By the laws of physics, DC electricity produces a magnetic field. Magnetic fields are bipolar--they have two equal and opposing forces, which we refer to as the North and South poles. In a DC motor, electrons start flowing from one side and flow through the circuit (in this case a coil of wire) to the other side. As they being their flow, they create a magnetic field which repels the permanent magnet towards the other side of the coil--so, the magnet begins to turn. When it reaches the horizontal point (where it would naturally stop and hover between the opposing magnetic forces coming from the two sides of the coil), a bit called the "commutator" flips the polarity of the magnetic field (gives the power to the side the magnet has moved towards), and the magnet is once again repelled--so, it continues turning. And so it is an endless loop, until the current is interrupted (the motor is switched off). Interestingly, a DC motor and a DC generator are essentially the exact same thing. If you shut off the power and turn the magnet by hand, you induce an electric current in the wire coil surrounding the magnet. Cool, eh? Anyhow, without a commutator, DC current does nothing in a motor. The current just flows through and out into the ground, rendering no force. It's harmless.
AC, on the other hand, works by acting as the commutator. You know how, in this country, we have "60 Hz" (hertz) current? What that means is that the current switches polarity 60 times per second. In an AC setup, there are three wires which come into your house: 2 load ("hot") and 1 neutral. One of those load wires is +110 volts, and other is -110 volts. 120 times every second, the power is switched from the +110 load to the -110 load (hence each is activated 60 times every second, hence 60 complete "cycles per second", hence 60 Hz)--this is graphically represented as a sinusoidal waveform. When speaking in terms of a motor, this force acts as the commutator. The +110 volts creates an electromagnetic force in the stator, which starts the rotor in motion. When the power "alternates" to the -110 volts, the opposite force ("pole", in DC terms) occurs and sends the rotor through the other half of its cycle. Speaking in terms of current flow, this is the fundamental difference between AC and DC: DC sends a constant current through a wire, where it either has an effect or doesn't, depending on what's in the circuit. AC doesn't actually send any electrons through a wire--it just rapidly polarizes and re-polarizes the free electrons which are already present in the conductor.
Speaking in simple terms, DC is not dangerous. You can touch a DC circuit and not be shocked--for example, if you touch a battery. When you touch both sides of a battery or other DC power source, current flows through you. Since you don't have a commutator inside, nothing happens. The current just flows harmlessly through one arm and out the other. AC, on the other hand, is extremely dangerous. Since it acts as the commutator, it attempts to turn you into a motor. If you touch both sides of an AC circuit--for example, if you stick your finger in a light socket, the current takes the free electrons in your body (because you're a conductor) and rapidly polarizes and re-polarizes them. You experience this as a painful shock. Also, since your heartbeat is controlled by electrical impulses, the AC current turns your heart into a polarized motor; this usually results in a nasty consequence such as death.
One of the most outstanding advantages that AC has over DC is its ability to travel long distances. AC can have its voltage changed, and then be sent over long distances from the power company to your house. DC, on the other hand, works on a scale of exponential decrease. The farther you send DC, the weaker it gets, and this force is pretty dramatic--to the point that we'd literally need a power company every few miles along each road.
So, back to the late 1800's.
Edison was a pig-head, and wanted DC used despite its obvious disadvantages, because HE, the great Edison, had perfected it. Tesla was pushing AC because it was more efficient.
So Edison went for the manipulation tactic--here comes his evil deed. He decided to appeal to the public fear of this new-fangled force called electricity. He would go down to the city pound and get a dog or cat, and then he'd go buy an old show elephant from a circus that had no more use for it. Then he'd hold an expo in downtown Manhattan where he'd hook the cat/dog up to DC and it would be fine; then, he'd hook the elephant up to AC and it would fry like a guy in an electric chair. This violently graphic (needless to say cruel) display was his method of pushing his DC theories. Anyhow, as history as shown, he lost the battle with Tesla.
The most common complaint about AC relates to fluorescent lighting and CRT computer screens--some people are very sensitive to the 60 Hz flickering. In the case of a computer monitor, you can set your refresh rate higher--85 Hz works for almost all folks. But you can't do that with a fluorescent light, so some people get headaches after a long day in a fluorescently-lit building.