Why Can Birds Sit Safely on Power Lines but Get Electrocuted When Touching Two?

[Cummings]

2 things,

First, I am asked to describe why a bird can sit on a powerline and not be electrocuted, yet if it spreads it's wings and touches two wires, it will be.

I can understand why it can sit on one. The powerline is all at the same voltage. And so there is no potential to motivate the electricity to move through the bird. It will take the easyest route: across the wire.
If the wire we to suddenly break between the birds feet, then there would be a potential accoss the bird and so current would flow. That, and it has no wire to bypass the bird!

Now, if the bird touched two wires, they would have to be at different potential for the bird to be electrocuted. Is this correct? As there is no potential difference there would be no current passing through the bird.
If there was a difference, then the bird would be electrocuted.


Second, car batteries are somtimes rated in ampere-hours. Does this designate the amount of current, power, energy or charge that is drawn from the battery?

I ruled out power as its the pruduct of the voltage and the current. the other three seem to closly related. Current is the flow of charge, charge carries energy. If i were to pick one, it would be charge. Because ampere's is current and that is the flow of charge coming out of the battery.

Thanks,
Cummings

 

[chroot]

1) is correct, your reasoning is good.

2) is also correct. Think about this way:

One ampere is one coulomb of charge per second. One ampere for one hour is one coulomb of charge per second for 3600 seconds, or 3600 coulombs. The ampere-hour is a unit of charge.

- Warren

 

[Cummings]

Discussing it with fellow students today, the powerlines, being AC would most likely be at different voltages due to their different phases. So, that would couse the potential difference neeced to electrocute a bird.

 

[chroot]

Well, most 3-phase lines are spaced more widely than a bird's wings could stretch, but yes, in principle you are correct.

- Warren