Benjamin Franklin invented
lightning rods in the 18th century, and the devices have been protecting
buildings and people from the destructive forces of lightning ever since. But
the details of how lightning rods function are still the subject of scientific
research.
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Although modern lightning protection
systems involve extra equipment that makes them more efficient, the lightning rod
itself is quite simple: a copper or aluminum rod set above the highest point of
a building, with wires connected to the ground. When lightning strikes a
building, it will preferably pass through the rod — the path of least
resistance — and then through the wires into the ground, protecting the
building and its contents from the extremely high currents and voltages
produced by lightning.
Less than 1 millisecond before the lightning touches it, the rod, provoked by the presence of the negative discharge of the lightning, sends a positive discharge up to connect to it.
But a rod does not wait for the lightning
to strike. Less than 1 millisecond before the lightning touches it, the rod,
provoked by the presence of the negative discharge of the lightning, sends a
positive discharge up to connect to it.
Brazilian researchers recently got lucky,
photographing this event with high-speed video cameras at very high resolution.
They captured the electric action in São José dos Campos, a city northeast of
São Paulo.
The photo opThe scientists were in the right place, at
the right time, and with the right equipment to capture 31 of these upward
discharges as they happened. With their location, about 150 yards away from the
lightning strikes, and their camera, a device that records 40,000 images a
second, they were able to take clear photographs and a slow-motion video of
what happens in that instant before the charge from the rod meets the charge
from the lightning bolt. The scientists’ study and photos were published in
Geophysical Research Letters in December.
It was not only lightning rods producing
these discharges, but also various corners of the buildings and other high
spots. In fact, “Any person standing in an open area can similarly launch an
upward connecting discharge from their head or shoulders and be injured by
lightning even when not directly struck by it,” said Marcelo M.F. Saba, a
senior researcher at the National Institute for Space Research in Brazil and an
author of the study.
“Any person standing in an open area can similarly launch an upward connecting discharge from their head or shoulders and be injured by lightning even when not directly struck by it.”
Does one kind of lightning rod provide
better protection than another?
“Some salesmen say that their lightning
rods are better than the rest,” Saba said, “but this is just sales talk. There
is no solid research on that. There are standards that have to be followed by
those installing lightning rods. That’s the best we can do for now.”
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