Birds can be seen perched on a high voltage power line yet seem unaffected by the high voltage. This is due to...
A) Low resistance of the birds compared to the wire, minimizing current through the birds
B) birds keeping only one foot on the wire, thus not completing a circuit
C) low capacitance of the birds (?)
D) Minimal potential difference across the birds
R = p(L/A)
The Attempt at a Solution
Assuming that current is constant across the entire transmisison line (it is right?), since the distance between the birds feet is very small, and since resistance is determined by length, the resulting resistence across that portion of wire would be very small.
Since current is constant across the wire, and the resistence is very small, then the resulting Voltage across those two points must be very small as well. The bird is effectively in parallel with the wire portion so it feels the same voltage,. Since the voltage is so small, it is essentially unaffected.
So that is why D is the correct answer.
What i dont understand is why a bird keeping only one foot on the wire wouldn't be a legitate reason either. There is no complete circuit so charge cant flow.
I was thrown off by the "low capacitance of the birds" statement, and since q=CV , I knew that would be false. But does capacitance even apply here? I thought it only applied when you had two parallel plates?
Finally, in this scenario, we know the voltage difference between the beginning and end of the wire (thats what we refer to when we say it's "high voltage" right?), current is constant throughout the wire right? I ask because it seemed odd to base my calculations of V=IR upon the constant current. Usually you use voltage to find the curent.