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Dec5-12, 11:13 AM
P: 12,053
In usual AC setups, you can assume that everything is in an equilibrium - the changes of current and voltage are small within the time electromagnetic fields need to propagate through your setup (about 1 nanosecond for 30cm, the speed of light). If that assumption is wrong, things can get tricky. A coil with 30cm diameter is not useful to convert GHz-signals (1 nanosecond per cycle), for example.