Serbia

030

Tesla Museum, Belgrade, Serbia

44° 48′ 19.38″ N, 20° 28′ 12.92″ E

The Man Who Lit Up the World

Thomas Edison is the name most people associate with electric light, but the man responsible for providing the electricity to lights and every other electrical device used today is Nikola Tesla (Figure 30-1). Tesla was born to Serbian parents in what is now Croatia, and lived in Hungary and France before moving to the U.S. in 1885. It was there that Tesla became the greatest electrical experimenter since Michael Faraday (see Chapter 75) and laid the foundations for modern electricity distribution.

Figure 30-1. Nikola Tesla

When Tesla moved to the U.S., he went to work in Edison’s laboratory, where he redesigned Edison’s DC generators and motors. He left after a disagreement about his pay, and after Edison had rebuffed Tesla’s attempts to interest him in AC electricity generation.

Later, Tesla and Edison battled bitterly and publicly over AC and DC electrical power. Tesla had joined up with entrepreneur George Westinghouse to build AC power stations, while Edison was pushing DC power. Edison tried to show that AC was dangerous, and to prove it he carried out executions of dogs, cats, horses, cattle, and even an elephant using AC power.

Ultimately, Tesla was proved right: AC power is easier to generate (the generators are simpler, cheaper, and more reliable), it can be transmitted much further (DC power was limited to short distances and necessitated power stations close to consumers), and its voltage can be converted using a simple transformer.

But Tesla’s inventions were not limited to AC power. Along with Marconi, he shares the honor of inventing radio (see Chapter 62), and he worked on wireless transmission of electricity, remote controls, vertical take-off and landing aircraft, directed-energy weaponry, robotics, spark plugs, and more. In all, he was awarded over 300 patents.

Nevertheless, Tesla died destitute, in room 3327 of the New Yorker Hotel in New York City. Two thousand people attended his funeral.

After his death, Tesla’s nephew and heir (who was also the Yugoslav ambassador), Sava Kosanović, arranged for Tesla’s personal effects to be removed from the U.S. and returned to Yugoslavia. Today the Tesla Museum in Belgrade houses his complete collection of books, writing, and objects, as well as his cremated ashes on display in a golden sphere.

The museum explains many of Tesla’s inventions, including AC power, and is the definitive place to understand Tesla’s life and work.

Practical Information

Information about the museum and details of Tesla’s life are available at http://www.tesla-museum.org/. If Serbia is too far away to visit, there’s also a memorial to Tesla on the Canadian side of Niagara Falls, where Tesla’s hydroelectric power plant was situated. See http://www.teslasociety.com/victoria.htm.

AC Versus DC

Direct current, or DC, is simple: it’s the type of electricity that batteries supply. In a DC circuit, electricity flows in one direction only—for example, from the positive terminal of a battery through a circuit to the negative terminal. Alternating current, or AC, changes direction cyclically, typically in the form of a sine wave (Figure 30-2).

Figure 30-2. AC voltage varying with time

AC varies in voltage from a positive maximum to a negative minimum over time. To generate AC power, a current can be induced in a pair of coils using a rotating magnet. The current varies as the magnet rotates. Since the magnet does not touch the coils, AC generators are reliable and simple. DC generators, on the other hand, require a more complex mechanism, with rotating brushes touching metal connectors that are used to change the direction of the current to keep it positive.

It’s simple to change the voltage of AC using a transformer (Figure 30-3). A basic transformer consists of a pair of coils, separated either by air or, more commonly, by some ferromagnetic material such as a bar of iron. Because the AC voltage varies over time, it creates a changing magnetic field around the coil it is connected to. This magnetic field induces an AC voltage in the other coil. The ratio of the number of windings of cable in the two coils determines the change in voltage (and current) across the transformer.

Figure 30-3. An AC transformer

But AC’s biggest advantage is in power transmission. Because AC’s voltage can be increased or decreased using transformers, it’s possible to choose the most appropriate voltage for a given situation (see Figure 30-4); that is, power transmission can use a very high voltage that is then reduced by a transformer before entering a home. Generators in power plants can produce power at a lower voltage than the transmission line, with the voltage being increased before transmission by another transformer.

Figure 30-4. Power transmission using AC

Because the voltage can be changed so easily, AC is able to take advantage of the fact that power loss in a cable is proportional to the square of the current. By increasing the voltage (perhaps to hundreds of thousands of volts), with a corresponding decrease in current, power can be transmitted over great distances. It can then be transformed to a lower voltage (and higher current) for delivery.

AC can also be converted to DC, using a simple device called a rectifier. Small electrical appliances (like cell phones) usually operate on DC, and power adapters both convert the AC supply to a low voltage and turn it into DC.