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J. Perelman
"Entertaining physics". Book 2.
Chapter 8. The magnetism. Electricity

BIRDS ON THE WIRES

Everyone knows how dangerous it is for a man touching electric wires tram or high voltage network when they are under stress. This touch is deadly to humans and large animals. There are many cases when a horse or cow kills shock if they touch the broken wire.

What can explain the fact that birds calmly and with impunity sit on the wires? A similar picture can be observed often in the cities.


Birds with impunity sit on electrical wires. Why?

To understand why such contradictions, we will take into account the following: body sitting on a wire birds is like the branch circuit whose resistance compared with the other branch (the short section between the legs of the bird) is enormous. Therefore, the current in this branch (the bird) is negligible and harmless. But if the bird sitting on the wire touched the pillar wing, tail or beak - all somehow connected with the earth, she would have been instantly killed by a current that rushed through her body into the ground. It is often observed.

Birds have a habit of sitting on a bracket high-voltage transmission, clean bill of current-carrying wire. Since the bracket is not isolated from earth, the touch of grounded birds to the wire, under the current, inevitably ends in death, How such cases are numerous, obvious from the fact that, for example, in Germany at the time took special measures to protect birds from destruction. To this end, the arms of high-voltage transmission lines were installed isolated perches on which the birds could not only sit, but with impunity to brush on the wire its beak. In other cases, dangerous places make use of special devices inaccessible to the touch birds.


Insulated roost for birds on a bracket on the transmission.

While the broad development that gets in the USSR growing network of high-voltage transmission, we should in the interests of forestry and agriculture to ensure the protection of the feathered population from destruction by electric current.

Entertaining physics J. Perelman

 




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