Repost: From MIT OpenCourseWare: Walter Lewin’s Lecture On Lightning

Full lecture here.

My brief summary:

So at room temperature, the electrical breakdown of dry air at 1 meter of distance is 3 million volts (at which point you have discharge sparks, visible light and heat, and moving air). 

Go and shuffle your feet on the carpet and touch the doorknob and if you see a spark of 3 mm it’s around 10,000 volts on average according to this calculation (a little prickle on the fingertip, maybe through your hand).

In the very large electrical field generated during a thunderstorm (400,000 storms every day on earth) you can get up to 300 million volts and more, blinding light and up to 50,000 degree F superheated air rushing outward in waves, or thunder.  The current should it ground itself through your body, can clearly kill you:


Through induction the stepped leader has made contact with the earth, and the return strokes travelling back up to the cloud are visible and audible.

**Of course, if you go and look at the nearest light bulb, the current passing through the resistive filament also produces light and some heat. 

That’s my oversimplification.  Listen to the lecture, it’s worth it.  A whole semester’s worth of his lectures are available for free at that link.

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