Question

Migratory birds are able to use the earth's magnetic field to navigate even when clouds and darkness prevent them from having visual references for their flight. The range of sensitivity of such birds extends to magnetic fields as small as about a third of the earth's natural field.

If such a bird is flying past a power line which carries 10⁵ amps, and if we assume that the minimum field detectable at 60 Hz is the same as the minimum field detected at DC, at what distance could the bird detect the presence of the power line?

Why will the real answer be much smaller?  (think about how power lines are arranged)

Answer 1

0-25 -4 - 2X10 252 m ma in sene So et held o Gee

But at real situation there are parallel and anti-parallel current flows in the power lines. So the enclosed current reduces and for that the magnetic field also reuces.