reactive power....
in [DSP]
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From: fisico32 on 15 Jul 2010 07:55 >On 7/14/2010 3:46 PM, fisico32 wrote: >>> On 7/14/2010 3:04 PM, Clay wrote: >>> >>>> ... Think about a resonant tank >>>> circuit where the energy moves back and forth between the inductor and >>>> the capacitor. >>> >>> I suspect that if he knew what a tank circuit is, he wouldn't have >>> needed to ask the question. He certainly wouldn't have asked it the way >>> he did. "What is this modern generation coming to?"* >>> >>> Jerry >>> _________________________________ >>> * I heard that a lot 70 years ago. >>> -- >>> Engineering is the art of making what you want from things you can get. >>> ����������������������������������������������������������������������� >>>>> >> Hi, I know what a tank circuit is: the L and C of the circuit cyclically >> exchange energy...but it seems strange that this energy exchange happens in >> free space and as we move further away from the antenna the energy exchange >> dissapears and both E and B fields have an equal amount of energy at any >> instant of time....The way and reason that happens is still not clear to >> me... > >That's the wrong interpretation, as I wrote before. If the E and H >fields were to become zero at the same time, what would regenerate them? >Constants aside, H = dE/dt and E = dH/dt, where the differentials are >partials with respect to time. > >Jerry >-- >Engineering is the art of making what you want from things you can get. >����������������������������������������������������������������������� > maybe a naive reply, but the fact that both E and H are zero at the same time does not mean that their derivatives are, so they will be nonzero at a later time. As far as what will generate either one if the other is zero, I am not sure...
From: Jerry Avins on 15 Jul 2010 09:26 On 7/15/2010 7:55 AM, fisico32 wrote: ... > maybe a naive reply, but the fact that both E and H are zero at the same > time does not mean that their derivatives are, so they will be nonzero at a > later time. As far as what will generate either one if the other is zero, I > am not sure... Both are sinusoidal, so if they were in phase, their derivatives also would be. They behave temporally like the electric and magnetic fields in the tank circuit that I'm glad to hear you understand. Energy shuttles back and forth between the capacitor and the inductor, i.e. the electric and magnetic fields. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
From: glen herrmannsfeldt on 18 Jul 2010 02:01
fisico32 <marcoscipioni1(a)n_o_s_p_a_m.gmail.com> wrote: (snip) > Hi, I know what a tank circuit is: the L and C of the circuit cyclically > exchange energy...but it seems strange that this energy exchange happens in > free space and as we move further away from the antenna the energy exchange > dissapears and both E and B fields have an equal amount of energy at any > instant of time....The way and reason that happens is still not clear to > me... Start with an LC circuit, slowly unwind the inductor, and unwrap the capacitor. (Maybe a rolled paper/foil capacitor.) That will shift the frequency, but also increase the radiated field. Eventually it will look like an antenna, but the L and C are still there. -- glen |