SCIENCE LAB SPECIAL : LIGHTNING RODS

 

Reaching Out

Lightning rods don't just wait for bolts from above.

Benjamin Franklin invented lightning rods in the 18th century, and they have been protecting buildings and people from the destructive forces of lightning ever since.

But the details of how they function are still the subject of research.

Although modern lightning protection systems involve extra equipment that makes them more efficient, the lightning rod itself is quite simple :

A copper or aluminium rod is quite simple : a copper or aluminium rod set above the highest point of a building, with wires connected to the ground. 

When lightning strikes it will pass through the rod  - the path of least resistance - and then through the wires into the ground, protecting the building from extremely high voltages.

But a rod doesn't wait for the lightning to strike. Less than one 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 the electric activity in Sao Jose dos Campos, a city northeast of Sao Paulo.

The 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.

From about 150 yards, or 140 meters, away from the lightning strikes, with a camera 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. [ Nicholas Bakalar ].