# I Induced potential - when do you have to consider EM waves?

1. Dec 7, 2016

### yabb dabba do

There's a long conductor carrying a 60 hz AC current. There's a second conductor parallel to the first current carrying conductor, and a hundred meters away from it.

I want to know what the electric potential induced by the changing B field is in the second conductor.

Theoretically I could use the biot-savart law to calculate B and then Faraday's law to calculate the induced electric potential from the changing B. However the alternating current also produces EM waves whose B field would induce an electric potential separate from that calculated by the biot-savart law as described above.

Is it justifiable to ignore the electric potential induced by the EM waves? Why/why not? Or am I just confused?

2. Dec 7, 2016

### Staff: Mentor

The usual rule of thumb is that you can use a "quasi static" approximation whenever the length scales are small compared to the wavelength of the EM waves. At 60 Hz the wavelengths are so much larger than 100 m that the quasi static approximation should be fine.

See this textbook, especially ch 8
http://web.mit.edu/6.013_book/www/book.html