~The Catch-All Drawer~
Thursday, December 18, 2003
BEN FRANKLIN'S KITE WAS STRUCK BY LIGHTNING?
Many people believe that Ben Franklin's kite was hit by a lightning bolt, and think that this was how he proved that lightning was electrical. A number of books and even some encyclopedias say the same thing. They are wrong. When lightning strikes a kite, the spreading electric currents in the ground can kill anyone standing nearby, to say nothing of the person holding the string! So what did Franklin actually do? He showed that a kite would collect a tiny bit of electric charge out of the sky during a thunderstorm. Electric leakage through the air caused his kite and string to become electrified and so the hairs on the twine stood outwards. Twine is slightly conductive, so the imbalanced charge spread to all parts of the kite string. Franklin used the twine to electrify a metal key, and tiny sparks could then be drawn from the key. (He used a metal object because sparks cannot be directly drawn from the twine, it's not conductive enough.) This suggested that some stormclouds carry strong electrical net-charge. It IMPLIED that lightning was just a large electric spark.
The common belief that Franklin easily survived a lightning strike is not just wrong, it is dangerous: it may convince kids that it's OK to duplicate the kite experiment as long as they "protect" themselves by holding a silk ribbon. Make no mistake, Franklin's experiment was extremely dangerous, and if lightning had actually hit his kite, he certainly would have been killed.
This is a clip from a science misconceptions thing that goes on and on - sort of a remedial tutorial for science teachers, nitpicking the faulty analogies that we were taught in good faith in school.
Tossed in by: R.G.B.
. . . Thursday, December 18, 20030 Comments:
