Lightning Rod

by Massy Dona   |   0 Comments  |   165 Views    |   0/5 Rating   |   Print This Article
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Apr 6th, 2012
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If an insulator (non-conductor) is placed in a gradually increasing electric field, it eventually breaks down and begins to conduct. The force exerted by the electric field on charges in the material of the insulator becomes sufficiently great to free them from their fixed positions. Lightning flashes, for example, are caused by a breakdown in the insulation of the air when a field of more than 3 million volts per meter is applied. The very large current that results consists mainly of electrons, which collide with air molecules, causing heating and the emission of light.

A lightning rod is installed in tall buildings to protect them from damages done by lightning. Tall buildings are more likely to be affected by lightning due to closeness with charges in the clouds. A lightning rod has a pronged tip joined to a thick copper conductor that runs down the outside of the building to a metal plate buried in the ground. A negatively-charged thunder cloud overhead induces a positive charge on the rod’s prongs (and a negative charge on the buried plate). An upward stream of positive ions above the rod constitutes a space charge, reducing the electrical forces between the cloud and the building.

The electric field inside a hollow conductor is always zero, no matter how highly charged it is. The inside of the conductor is completely shielded from electrical discharges or other electrical phenomenon outside it. Thus the inside of an aircraft or a car is generally unaffected if it is struck by lightning.

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