Just to toss an extra little hand grenade into the room...
... does this current which may or may not flow through a capacitor, obey Ohms Law?
JimB
but I dont see any mention of voltage in my post,
Last time I looked capacitors were made of material.
We need you here in SA as a private weapon.......
You will make the people you teach so crazy that they will commit "you know what" in their masses. I have a place for you to stay. Wanna chance it??
And then, South Africa will be truly free.
What about the professor referenced by nsaspook in post #37 of this thread, who specifically says that current does not exist through a cap?
Let's be fair and accurate here.
Prof. Lewin was talking about displacement current in the beginning parts of the lecture. He is basically making the same mistake (although it may be a deliberate mistake in his case) I made in the other thread where I attributed all current associated with "going through" to displacement current. This is a natural approach/mistake to make when you are trying to describe displacement current. His comments about no charge flow current through the dielectric are relevant for vacuum dielectric caps (or air caps practically). Practical caps with material dielectrics have polarization current. Later in the lecture (time: 21:35 to 22:50) Prof. Lewin clarifies and corrects his previous mistake and mentions that displacement current does not involve real charge flow, but polarization current in the material is a real charge movement (I'll say movement rather than flow). "There is indeed a current" are his exact words at that point in the lecture. So it's not fair to pick and choose one statement to favor your opinion. I could quote the other part of the lecture and make the exact opposite point. In fact, both statements (although they contradict) are part of the full truth.
So, the idea of no charge movement (or flow) is attributable only to displacement current for vacuum, but not polarization current for material dielectrics. For any capacitor (even one with super high permittivity) there has to be some contribution from displacement current. So, even if >99% of the wire drift current can be associated with polarization current in the material, there is still missing charge flow that must be associated with displacement current which is not actual charges flowing (but is still called a current).
So we are seeing even an outstanding professor and scientist like Prof. Lewin will not speak perfect literal correct facts at all points in the teaching activity, especially when speaking (as opposed to writing where there is more time to think). It's simply too difficult to be perfect. Instead, teachers repeat points several times and show things from different points of view, and the sum total of what they say is correct (hopefully), when taken in full context. Sometimes the omissions and false statements are deliberate, with the teacher knowing that too much information will overwhelm. So they sometimes lie a little bit until the critical concepts are absorbed, and then they later clarify and include the pertinent details.
So how does all of this relate to the principle of power factor shifting in AC circuits then if no current is being conducted or whatever some want to describe it as?
That and what is my amp clamp reading when I clamp it over the conductor going to or from a capacitor that is being used in an AC circuit?
I also don't think he was trying to fool us. I think he is trying to educate us. I think he does his job better than most.I don't think he was trying to fool us.
You will always measure the current that you clamp around, no matter where you place the clamp. You can even place in around the cap because displacement currents, drift currents, polarization current or any other current you can think of creates the same integrated magnetic field around the loop. The clamp meter is based on the modified Amperes' Law that Prof. Lewin discusses in the lecture 18 referenced above.what is my amp clamp reading when I clamp it over the conductor going to or from a capacitor that is being used in an AC circuit?
Ratch,
So, the idea of no charge movement (or flow) is attributable only to displacement current for vacuum, but not polarization current for material dielectrics. For any capacitor (even one with super high permittivity) there has to be some contribution from displacement current. So, even if >99% of the wire drift current can be associated with polarization current in the material, there is still missing charge flow that must be associated with displacement current which is not actual charges flowing (but is still called a current).
Steve
You guys are all wrong about this stuff! Even us dummies know it a depends on the smoke. Let the smoke out and no more working.
Hi MrRB,
Well you are arguing with me about something telling me that 'your' single view is better than the 'dual' view where we 'know' that there are two different approaches.
...
... but you cant tell me that i am not allowed to question or think about that second view, and surely you cant tell me that i cant talk about it can you?
...
... It's not a topic for a beginner and i never said it was, but we are not beginners are we, so we can talk about it. ...
Ratchit said:... Do your students ask how current can exist through a cap when the dielectric is an insulator? What about the professor referenced by nsaspook in post #37 of this thread, who specifically says that current does not exist through a cap?
Well, you can fill up one side of the capacitor with blue electrons and the other with red electrons. Then apply an AC current. If you have trouble colouring the electrons, you could try the equivalent experiment using dyed water with a rubber diaphragm in place of the dielectric.
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