Science Questions

Why can birds sit on a power line and not be electrocuted ? Mary, Cottenham, phone

The reason that birds can sit unharmed on power lines is that no current flows through them because they are not completing the electrical circuit by sitting on one line only. Rather like water flowing down hill, electricity needs to flow down an electrical hill, otherwise known as a potential difference. So if you connect the plus side of a battery to the minus side current flows because there are lots of positive charges at the plus pole and very few at the negative, so the current flows to try to equal things out. So going back to the bird sitting on a power line, no current flows through the bird because it has the same charge as the wire it is sitting on. If it were to straddle a positive and a negative line, on the other hand, it would certainly be curtains ! Ditto if it put one leg on the ground and another leg on the wire. Under these circumstances there is a big difference between the amount of charge in the wire and the charge on the ground, so electricity would flow through the bird in an attempt to balance things out.

July 2002