The bifilar pancake coil at its resonant frequency

[evostars]

some shout: The Earth is flat! you fools,  it has been proven! the earth is the center of the galaxy! you fools it has been proven.

clearly we live on the same earth,  and we now believe its a sphere (most of us).

maybe in the future we find out its a hollow sphere,  and we live in the inside.

What I'm trying to say,  is its all a matter of perspective.

you can see the electrons and atoms as particles, because it was proven,  as was the flat earth.

I never believed this to be true. all is light,  all is made of light fields and vortexes. particles are made up to under stand the complexity of the fields easier. but its only a trick,  that has its limitations. even the dielectric and magnetic fields are made of the same stuff. light.

please believe your own truth, which ever works best for you.

[TinselKoala]

Consider the image below, describing a very complicated circuit.

With the switch closed, does the LED light? In which direction does the current (conventional) flow through the coil?

When the switch is opened, does the LED flash? In which direction MUST the current flow from the coil if the LED is to flash?



People may agree or disagree about opinions. But as Richard Feynman said...

It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong.

[Jeg]

Consider the image below, describing a very complicated circuit.

With the switch closed, does the LED light? In which direction does the current (conventional) flow through the coil?

When the switch is opened, does the LED flash? In which direction MUST the current flow from the coil if the LED is to flash?



People may agree or disagree about opinions. But as Richard Feynman said...

Is there any chance to confuse counter emf with current? If current doesn't reverse then why a secondary added to the coil in your drawing gives the attached waveform? Blue is drain, yellow is across the secondary. Switching is at low side and not high as in your drawing but the end result is the same. Notice that when current is flawing, secondary is negative. When switch opens secondary changes direction and goes to positive. Reverse of counter emf across any secondary indicates reverse of current flawing across a primary. Led lights because you apply in the right direction a voltage potential. If current was flawing at the same direction across your primary, then across the secondary we would see a negative value which goes even more negative when switch is open. Isn't that true?     

[Jeg]

Purple is current across the primary. Yellow is the voltage across the secondary. I see a current which increases and suddenly changes to the other direction towards zero.

I think that changing direction of current is not the right term to describe it, and there lays all the misunderstanding. It is more a rapid break to the current flow and not an actual reverse of current. But coil will react by changing voltage polarity.

[TinselKoala]

@Jeg:   look at the sign (polarity) of the EMF in Faraday's Law of Induction:

https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction


Is it possible that "some people" are confused about this? Certainly, just look back in the thread for examples. But we are not talking here about current/voltage induced in a secondary, we are talking about what happens to the current in a single coil when the power to that coil is interrupted.

If you look at the schematic, you will see that when the switch is opened the _bottom_ end of the coil becomes Positive in analogy to a battery. This is the only way that the LED can flash, since it is reverse-biased when the switch is closed. So when the switch is opened, you can think of the voltage on the coil as "reversing" but the CURRENT definitely does not. When the switch is opened, the coil tries to resist changing in its magnetic field and to do this it must keep current flowing in the _same_ direction as before, for as long as it can. If there is no path for the current to flow, the _voltage_ increases as the coil attempts to keep current flowing, until something breaks down, like a spark. This is the source of the great "inductive spike" in _voltage_ that happens when the current through a coil is interrupted. This is also why we put reverse-biased diodes across, for example, relay coils to allow the current someplace to go, so the voltage rise doesn't damage something. The diodes are only reverse biased when the coil is powered! When the power is removed, the _voltage_ reverses so the diode is no longer reverse-biased and the _current_ has someplace to go (back into the coil through the diode, always flowing in the same direction as it did when the coil was powered.)