One of the most stunning electrostatic phenomena are
lightning strikes that accompany
electrical storms.
Thunderclouds often have a
positively charged upper portion, a
negatively charged lower portion (each charge being approximately 30
coulombs) and a
neutral central area. The negatively charged base of the cloud induces a corresponding positive charge on the
earth below the cloud. This in turn sets up a strong
electrical field between the cloud and the earth. Forked lightning flashes occur when the
electrical field is so great that the air
ionizes, or breaks up into positively and negatively charged
ions. The positive ions flow up to the base of the cloud,
neutralizing the negative charge there, while the negative ones flow down to earth, neutralizing the induced positive charge there: this ionization is visible as the lightning flash.
The transfer of such a large charge over such a short period of time produces temperatures in the air as high as
30 000 K. This sudden heating causes the air around the strike to expand rapidly, setting into motion an intense longitudinal vibration of the air, which can be heard as
thunder. Since
light travels much faster than
sound, to a distant observer the thunder will arrive much later than the
lightning. Obviously if one were struck by lightning, the lightning and thunder would occur almost simultaneously, but unfortunately one would unlikely notice this phenomena if one were in such a situation. As lightning strikes a building, it will flow to earth through the stonework and produce intense
heat. Any moisture in the lightning’s path will boil, producing pockets of high-pressure
steam, which can easily crack the masonry, often causing severe structural damage to the building. This is where
lightning conductors come in. They consist copper strips reaching from the highest point of the building to the earth causing any lightning charge to flow directly to the ground, leaving the building unaffected.