Stephen A. Lawrence wrote: [snip] > However, there's something here that bugs > me whenever I think about this stuff. > > Michel Jullian wrote: > >> Energy stored in a pure inductor is fully recoverable actually > > Yes, of course, v = -L dI/dt and what goes in must come out. > > But as someone mentioned, when you turn on the power an EM wave travels > out from the inductor at C, carrying energy. How's that energy get back > to the inductor again when we open the circuit? If it doesn't, then > that formula, v = -L dI/dt, must not be quite correct.
The fundamental equation appears correct. What is commonly misunderstood is that electro-magnets cannot be purely inductive due to radiation resistance. There's wire resistance, and there's radiation resistance. > Related issue: If the inductor is part of a transformer the "other > coil" absorbs energy and that doesn't come back out (or, rather, it > comes out the "other side" of the transformer). But if we separate the > primary and the secondary coils by significant distance, the primary > doesn't know for a long time that the secondary absorbed some of the > energy -- so how does it know it shouldn't give back the full complement > of energy to the power supply during the second half of the cycle? In such a case energy from the primary is radiated. This causes radiation resistance on the primary coil. It would be the goal of the secondary to capture as much radiation as possible. > This is particular interesting with regard to an antenna, which seems > like it's just a transformer with a lot of distance between primary and > secondary. An antenna is basically just an ideal inductor, yet it > radiates away power that doesn't come back out at the terminals. Radiation resistance. > What's the difference between an antenna and a simple coil, _aside_ from > the fact that we "think about" an antenna as broadcast device and a coil > as an energy storage device? As you know, coil designers try to eliminate as much radiation resistance as possible. Antennas are designed to do the opposite. Both have inductance and radiation resistance. Regards, Paul Lowrance ____________________________________________________________________________________ Bored stiff? Loosen up... Download and play hundreds of games for free on Yahoo! Games. http://games.yahoo.com/games/front
