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The Debunker: Do Lightning Rods Attract Lightning?

by Ken Jennings

In July 1820, Danish scientist Hans Christian Oersted published a groundbreaking pamphlet on the relationship between electric current and magnetic fields, effectively kicking off our modern electric age. You may think about electromagnetism every July when you look at your power bill and see how it spikes when your air conditioner is on. In honor of everyone getting zapped by the electric company this month, we've asked Jeopardy!'s Ken Jennings to set us straight on some high-voltage misconceptions about electricity, correcting all of our shocking ignorance. He knows "watts" up. He keeps current.

The Debunker: Are Power Lines Insulated?

Lightning kills as many as 24,000 people every year, and injures ten times as many. It's a real safety issue, not one of these overhyped 11-o'clock-news dangers, like shark attacks. When you've got bolts of electricity blazing out of the sky with a currents of 50,000 amps and temperatures up to 50,000 degrees, you don't want to fool around. Thank goodness Benjamin Franklin took the time in 1749 to dream up the lightning rod, a grounded metallic terminal that can be placed atop a lightning-vulnerable building. This way, lightning can be drawn to earth without causing too much damage on the way.

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But did you know some people are skeptical about lightning rods? This is more or less for the same reason that some gardeners don't use bug traps: you'll have to attract more bugs to the area, even if most eventually wind up in the trap. Along the same lines, some people fear that lightning rods will actually attract more lightning strikes to their surroundings. Who knew that lightning rods were such a, er, magnet for controversy? Beacon for controversy? I wish there was a better metaphor here…

But the "bug trap" analogy shows a fundamental misunderstanding of how lightning works. When a lightning bolt advances downward through a cloud to earth—meteorologists call this 60-miles-per-hour burst of electrical propagation a "step leader"—it doesn't "know" where it's going to hit. The step leader doesn't "decide" on a target, in fact, until it's just 100 meters or so away. So a lightning rod doesn't raise the risk of lightning striking a particular area. It's just pretty good at redirecting a bolt away from trees or rooflines or people in those last few meters.

But don't feel bad if you misunderstood lightning rods. Even their inventor was fooled, it turned out. When Ben Franklin first wrote about lightning rods, he believed that they would actually help dissipate charge, by creating a strong electric field around the pointy end. In other words, a lightning rod would repel or prevent lightning! Researchers now generally agree that Franklin was right in theory, but the ionization effect he described only extends a few meters above the terminal, not enough to affect storm clouds at all. Besides, would you really take advice on lightning from a guy who flies a kite during a thunderstorm?

Quick Quiz: What longtime Detroit Red Wing and hockey legend is now the general manager of the Tampa Bay Lightning?

Ken Jennings is the author of eleven books, most recently his Junior Genius Guides, Because I Said So!, and Maphead. He's also the proud owner of an underwhelming Bag o' Crap. Follow him at ken-jennings.com or on Twitter as @KenJennings.