Edison, Tesla, and Electrocution
In the late 1800s, Thomas A. Edison had invented the light bulb. This had such a great impact on the world, that even today we uses images of a person thinking -- and the image of a light bulb suddenly appearing in his thoughts -- as a cartoon of a person having a great idea.
The man who most disliked Edison's invention was a man named John D. Rockefeller, who had made a fortune selling oil. At that time, oil was used almost exclusively for heating and lighting. Electricity (which could be made by burning coal -- which boiled water, which ran a turbine, which ran a generator), could make his oil virtually worthless. Fortunately for him, right about that time, improvements in oil-driven engine technology (in particular, the "internal combustion engine") made possible a new invention: the auto-carriage, also known as the auto-mobile. So Rockefeller's fortune was preserved.
Edison wanted to "electrify" New York City. His vision was to put metal wires on poles above the city streets, to carry current to every house. Because energy is lost in those wires (from their resistance), the energy could not be transported very far. But he saw that a creating no real problem: he would place an electric power generator in every neighborhood, so the wires would never be more than a few blocks long.
Edison had hired a very talented engineer named Nicholai Tesla. But Tesla had quit in a huff. Tesla claimed that Edison had patented all of Tesla's ideas in the name Edison, and had not given Tesla the monetary rewards that he had promised.
Tesla had become enamoured with the idea of "alternating current", AC for short. In alternating current, the voltage and the current oscillated, positive and then negative and then positive again, 60 times every second. If one used AC instead of Edison's DC (for "direct current") then you could make use of a wonderful invention called the transformer. (The transformer was invented in 1860 by Antonio Pacinotti. Transformers used to generate extremely high voltages are often called "Tesla coils". ) A transformer used the fact that a wire with current in it creates a magnetic field. If the current varies, then the magnetic field varies. As I said in class (the jumping rings demo), a changing magnetic field will create a current in a second wire. The amazing part of all this is that the voltage in the second wire could be very different from the voltage in the first wire. What the transformer transforms is the voltage.
Start with low voltage AC, put it through a transformer, and what comes out is high voltage AC. The advantage of high voltage AC is that it carries power with very little electric current. That means that there is very little power loss in the wires, so the power can be sent for long distances using long wires. There would be no need to have electric generating plants in every neighborhood. When the electricity got close to a home, it could be transformed again, to convert the electricity to low voltage, which is less dangerous to use. A small transformer could be place on the top of the pole that supported the wires. (Most neighborhoods today have just these transformers on the pole tops. When they burn out or otherwise fail, the neighborhood is left without electricity, and the transformer must be replaced or repaired. PG&E usually does this within a few hours.)
AC turned out to have such an advantage (no neighborhood power plants) that it completely won out over Edison's DC. Telsla got the support of George Westinghouse, and their system turned into the one we use today. The voltage in our homes is only 110 volts AC. (Actually 110 is an average voltage; the voltage varies between about -150 volts and +150 volts.) The voltage changes from positive to negative and then back to positive 60 times per second, i.e. 60 Hertz, abbreviated 60 Hz. In Europe, they use the slower frequency of 50 Hz, which is why their lights and their televisions flicker. (Our eyes don't notice flickering if it is faster than about 55 Hz. I think the Europeans made a dumb mistake, all for the purpose of trying to be a little more metric than the US. For a while, they also tried 50 seconds to the minute, and 50 minutes to the hour, but they gave up -- people couldn't get used to it. But the 50 cycles per second remained.)
But Edison did not give up without a fight. He tried to convince the public that high voltage was too dangerous to use in cities. He did this with a series of demonstrations of the danger, in which he invited the public to watch as he used the Westinghouse/Tesla high voltage system to electrocute puppies and other small animals. Eventually he put on a demonstration using high voltage to kill a horse. Edison had also inventeda motion picture camera, and so he was able to make a movie of the electrocution of an elephant. The movie still exists. It is too fuzzy to be really grizzly, and you can watch it on the web by clicking Edison electrocutes Elephant. Nevertheless, I find the movie horrifying. Nathan Bramall found that the name of the elephant executed was "Topsy" and she was a "bad" elephant who had been condemned to die for having killed three men. Apparently the Society for Prevention of Cruelty to Animals approved of the execution, since they thought it would be inhumane to hang Topsy. See the Topsy page for the details. In an unrelated quote, Edison said, "Non-violence leads to the highest ethics, which is the goal of all evolution. Until we stop harming all other living beings, we are still savages."
The ultimate horror, of course, was to show that high voltage electricity could kill humans. To do this, Edison convinced the State of New York to switch from hanging its condemned inmates, to electrocuting them. He also argued that this method of execution was more humane -- a conclusion that most modern observers think is exactly backwards. But New York adopted the method, and then so did several other states.
Despite the publicity created by all these things, the advantages of AC won the day, and that is what we use now.