Deeper into Jeopardy! LI: Science & Geometry – $800

Jeopardy! category: SCIENCE & GEOMETRY (19-10-2015)

$800 clue: The first electric light was an arc lamp with two rods of this element

Correct response

The gist: Not any of the ones we normally associate with light bulbs today. Sir Humphry Davy‘s original arc lamp, designed and produced in the first decade of the nineteenth century, consisted of two rods of carbon hooked up to an electrical source. The tips of the rods were touched to complete the circuit (that is, electricity began running through them). When the tips of the carbon rods are separated, the electric charge still wants to flow, and it can make the jump if the gap is kept small enough. As the electricity jumps, or “arcs,” across, it heats the tips of the carbon rods to several thousand degrees, vaporizing bits of it. The really energetic (that is, hot) carbon vapor ionizes easily with the surrounding air, emitting light as electrons fall from higher-energy to lower-energy states – the same principle behind lightning.

This ionizing action gives off a very intense, bright, white light, which became the first practically produced electric light in history. Arc lamps were commonly used throughout the nineteenth century, and even into the twentieth, after incandescent lightbulbs had largely replaced them, for certain applications that required very bright lights like movie projectors. In the U.S., arc lamps were one the early major competitors to Thomas Edison’s lightbulb, a problem that was solved when the Thomson-Houston Electric Company, the largest producer of arc lamps, merged with Edison’s General Electric in 1892.

An antique carbon arc lamp

The clue: I certainly had no idea what the correct response to this one was, and neither did the contestants, who guessed, incorrectly, tungsten, magnesium, and copper. Tungsten, of course, it what’s used as the filament in modern lightbulbs, and would have been my guess if I was forced to. Magnesium is known to give a brilliant light when heated, and copper is commonly used in electrical systems, which I suspect were the motivations behind those guesses. I honestly don’t know why the writers thought this was an $800 clue. If you have an idea, please let me know in the comments.

In Jeopardy!: What can I do with “carbon”? Not much, given its over 400 clues in the J!Archive. A search for “carbon arc” gives too many too (a-r-c is just too common a three-letter sequence for the J!Archive’s search system). “Carbon lamp” gives just two clues: this one and one about “lampblack,” a pigment created by incomplete combustion of carbon. Just for fun, I’ll add that Humphrey Davy is in four clues, two for his discovery of nitrous oxide (aka laughing gas), one for his discovery of electromagnetic induction (which also mentions his teacher Michael Faraday), and one for his creation of a safety lamp for coal miners that used a safely-contained flame that didn’t ignite ambient methane gas.

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