Mesmerised by the explanation.. The fact that there is no charges flowing even though the current still persists. Gives a better visual over the displacement current. Thanks!
It's strange for me about those 3 types of current. I would say that 1) and 2) are the same, as sigma=q*n*miu and v=miu*E. I think diffusion current is missing here and probably was intended to present: j[diffusion]=q*D*dn/dx, where D is diffusion coefficient expressed through Einstein relation: D=miu*k*T/q. k is Boltzman constant and T is temperature in kelvins. Tell me if I am wrong.
There is no positive flow from one end and negative flow from the other end. Please. Take the blue line at 2:13 and throw it away. It is electrons flowing in one direction.
A Capacitor is a Transmission Line which has a low value of Zo. We do not need a changing field for energy propagation. Displacement Current does not exist. What is observed within a Capacitor when a changing voltage is applied is that the energy flowing one way is not equal in time to the energy flowing in the reverse direction and so we may measure a supposed current, which is merely the difference at any point in time between this flow. For more please look up Oliver Heaviside "We reverse this".
A capacitor is a transmission line? By definition anything is a transmission line but to define a capacitor as a transmission line is foolish. A transmission line needs a close reference to be usable otherwise. Why even bother mentioning such comment. Also displacement current does exist. Stop misguiding people
QUESTION: The Amp-meters in this video show opposite signs. Assuming that moving electrons represent an electric current, (I think) the current-direction in the upper-half of the circuit should be the same as the direction in the lower-half. Both counter-clockwise! So shouldn't the Amp-meters have the same sign?
Actually what i thought was one plate is charged positively. This causes induction in the neighbouring plate and so it gets positively charged. I don't understAnd how tge negativie charges can flow like that to that plate.
Rahul I don't have an intuitive explanation but the equal sign in Gauss' law says the change in flux through a closed surface is exactly the same things as adding or removing charge in the volume. I think the mental image of moving little charge balls applies better to mass than charge. It is simply a poor analogy to what is really going on which is that charge is only "felt" when you have field lines. A real physicist will probably jump all over this explanation, but that is my mental picture.
Is there anyway to relate change of Electric flux (which behaves as current) to the motion of charges (which clearly is current) ? It is a little difficult to digest the explained fact without any apparent underlying phenomenon to Displacement current.
A bit late here but yeah at t = infinity the total current will zero out. this is only true for a varying E field which is occurs when you close the circuit AKA turn it on. (Transient response or unit step or heavy side)
Another way to prove this theorem would be using the point form of Ampere's Law. Because without taking into account the displacement current, you would get a contradiction.
since there is no conduction current through the capacitor, does that mean that the current flowing externally through the wires of the capacitor connected across a voltage source is actually drift current as the plates are charged up to the respective battery terminal polarities? Or, a better question is, what IS the current that flows between the battery and the leads of the capacitor to when the plates are charging to their respective polarities (since current is not really flowing through the capacitor and completing a loop) from battery + to battery -?
With respect, it is not what you said that I object to. It is what you didn't say. A moving charge (i.e. a conduction current) establishes a magnetic field. But a time-varying electric field also establishes a magnetic field by Ampere's circuital law. And so, from the perspective of the magnetic field, the induced magnetic field doesn't "know" whether it was established by a moving charge or by a time-varying electric field. To talk about displacement current (the partial derivative of D with respect to t) without talking about the curl of the induced magnetic field is to leave students somewhat in the dark. The "stretching" of the mind regarding what a current is comes down to Ampere's Law: If the curl of a magnetic field is not zero, you are dealing with some kind of current. It may be conduction current (J = sigma*E) or displacement current (partial derivative of D with respect to t). Either way, you have a non-zero curl of the magnetic flux density. And that is as good a general definition of current as any. To understand displacement current, students need to understand curl, Stoke's theorem, and Ampere's generalized circuital law.
is there any relation between displacement current and the current of the voltage source. what you are saying is displacement current would be the same whether my voltage source is 12v 9A or 12v 1mA
4:07 Is the top equation where voltage is equal to the Line Integral of the Electric Field supposed to have a negative? I guess using the magnitude of the Field changes that?
Can the current flow through the capacitor even if the current is DC?? I thought that impedance becomes infinite for capacitors when frequency is zero. Can anyone explain about my question please?
Yes. Using AC math, we know at time = infinity the impedance of a capacitor becomes zero. But with DC math, we can see what happens before that! Going from frequency domain to time domain might involve fourier analysis. Current will flow through the circuit and a displacement current will appear and exponentially decay to zero at time = infinity.
Darklink9110 almost.....except the current through the wire is also a displacement current. In case you're having trouble with that, ask yourself how quickly that capacitor charges. Then remind yourself how quickly electrons "flow" in a conductor. Correct, electrons do not"flow" anywhere near the speed of light. This video presents a very naive discussion of displacement current......flow of electrons and current meters only have meaning when electromagnetic propagation is being slowed down *considerably* by the distributed resistance of a transmission line or other circuit elements. With a voltage connected directly to a capacitor as drawn, there is only one conduction current and that is zero......it is all an instantaneous displacement current caused by an electromagnetic field traveling at whatever the speed of light is in that medium. As drawn, at no time is there ever any measurable current which is dictated by the speed of electrons in a conductor.....good luck finding those ammeters which apparently have a measurement time close to the speed of light! As drawn, the operation of the entire circuit is dictated by electromagnetic wave propagation and at no time by "flow" of electrons....ie. there is no "conduction current" that can ever been measured by those ammeters in the circuit drawn (other than zero at dc) Dear powerpoint professor....if you're going to segway into displacement current like this, please just stick a resistor in your conduction current circuit and stop confusing another generation of engineers. Just a resistor would show you really know the difference.
Simple answer: Impedance becomes infinity when the frequency is zero, but that does not happen instantenously. Time depends on the capacitance of the capacitor.
You stopped short of explaining the mechanism of displacement current flow through a capacitor in a vacuum. Without an explanation for that, doesn't it seem like an incomplete model?
Yes, I agree. Everything in this video was clear, but I was really hoping for an explanation of the above. I also found this video helpful: czcams.com/video/zTuLT8zrDnI/video.html
Hey, I believe the same question has been bogging my mind for the last two days. I think this post pretty much cleared the relationship between change in electric flux and the resulting conduction current equaling to the displacement current: physics.stackexchange.com/questions/83715/what-constitutes-displacement-current
I believe that the charge of an electron is not really concentrated in the place where we say that the electron is located, but its “carrier” is the whole field of the electron. Its highest density (D vector) is around the electron, but then continues to "infinity". Therefore, in Maxwell's equations in differential form, ie valid for the element of continuous space, we do not use the expression dQ/dt, but dD/dt (partial derivative). Vector D represents the charge density per considered spatial element, although the electrons themselves may be far away in the metal electrodes. dD/dt is then the density of the Maxwell displacement current flowing through this dielectric element.
SAME wonder that we make in >>>>how votage can be buildt across a coil it is just a wire then we learn that voltage is not because the resistevity of the wrie rather it is due to current struglle to build the megnatic field in the cam the same wonder bulit again how should current cross the cap while its an open circuit same solution the ekectric field is the media by which the current travels this is the most intuitive thing if you get the coil you get the cap
Shit. This is my second time watching this video. At first I didn't really get what displacement current is. In the capacitor example, I was bent on the idea that when the capacitor is charging, charge moves from one plate to another, that's it, end of story. But I think I get it now: That in order to satisfy circuit theory, Kirchoff's current at a node, we must define a displacement current, such that the current leaving one plate of the capacitor, is equal to the rate of change of the electric field, which is "the current entering the plate". But, now that I think about it, displacement current in this scenario is just another way of saying i = c dv/dt, just in terms of the electric field, hmm...
Mby we dont understand current at all.. mby its compleatly different story. I believe there is much more simple things to meshure and it has strong ties with everything. But im just a regular fool. I know a little and i would like to know more but info doesnt suck up for me if info is not in the right order as 1-100. Haja.. go humans go!
Displacement current through the cap. ? seems like no permanent break down of the dielectric if charges move through it !!! you can't even say that whether physically there is moving charge or not this is how we define it !! as engineers it makes no sense at all you're just messing ...... Engineers apply science after full understanding of the concepts not creating it ... please if you have reasonable explanation try to do it but you have done is a mess
why do profs think power points are good. you should be doing every lecture by hand. if you use power point, no one remembers anything. it's useless for math, and you're a terrible prof if you use ppt.
Mesmerised by the explanation.. The fact that there is no charges flowing even though the current still persists. Gives a better visual over the displacement current. Thanks!
''and nobody said that this stuff was going to be easy!"
hilarious but true! :D
You had me at "mathematical mumbo jumbo" :D. But definetly one of the best explanations on YT. Thanks for your efforts!
Thank you! Touched on this briefly in my physics 2 class, but there was a lot of hand waving going on. Thanks for a more in-depth explanation.
Beautifully explained. Real easy to understand. Thanks a million!!!
Thank you very much !
It's strange for me about those 3 types of current. I would say that 1) and 2) are the same, as sigma=q*n*miu and v=miu*E. I think diffusion current is missing here and probably was intended to present: j[diffusion]=q*D*dn/dx, where D is diffusion coefficient expressed through Einstein relation: D=miu*k*T/q. k is Boltzman constant and T is temperature in kelvins. Tell me if I am wrong.
This is an excellent explanation!
Excellent video!
nice video!
There is no positive flow from one end and negative flow from the other end. Please. Take the blue line at 2:13 and throw it away. It is electrons flowing in one direction.
A Capacitor is a Transmission Line which has a low value of Zo. We do not need a changing field for energy propagation. Displacement Current does not exist. What is observed within a Capacitor when a changing voltage is applied is that the energy flowing one way is not equal in time to the energy flowing in the reverse direction and so we may measure a supposed current, which is merely the difference at any point in time between this flow. For more please look up Oliver Heaviside "We reverse this".
nah, how do you explain one wire transmission if not by displacement current?
A capacitor is a transmission line?
By definition anything is a transmission line but to define a capacitor as a transmission line is foolish. A transmission line needs a close reference to be usable otherwise. Why even bother mentioning such comment. Also displacement current does exist. Stop misguiding people
I did the exp, and it works, Thanks
"essentially" he is correct
There are vast distances between atoms in a conductor. The bottom line is that all current is displacement current.
QUESTION: The Amp-meters in this video show opposite signs. Assuming that moving electrons represent an electric current, (I think) the current-direction in the upper-half of the circuit should be the same as the direction in the lower-half. Both counter-clockwise! So shouldn't the Amp-meters have the same sign?
Actually what i thought was one plate is charged positively. This causes induction in the neighbouring plate and so it gets positively charged. I don't understAnd how tge negativie charges can flow like that to that plate.
Rahul I don't have an intuitive explanation but the equal sign in Gauss' law says the change in flux through a closed surface is exactly the same things as adding or removing charge in the volume. I think the mental image of moving little charge balls applies better to mass than charge. It is simply a poor analogy to what is really going on which is that charge is only "felt" when you have field lines. A real physicist will probably jump all over this explanation, but that is my mental picture.
Good job!
Good explanation .
good video
Thank god i did not go to college. This could have been explained so easy.
Is there anyway to relate change of Electric flux (which behaves as current) to the motion of charges (which clearly is current) ? It is a little difficult to digest the explained fact without any apparent underlying phenomenon to Displacement current.
j = epsilon dE/dt. If E is constant (which it is), wouldn't j come out to be 0 here?
Hemabh Ravee have you found the answer?
A bit late here but yeah at t = infinity the total current will zero out. this is only true for a varying E field which is occurs when you close the circuit AKA turn it on. (Transient response or unit step or heavy side)
Another way to prove this theorem would be using the point form of Ampere's Law. Because without taking into account the displacement current, you would get a contradiction.
since there is no conduction current through the capacitor, does that mean that the current flowing externally through the wires of the capacitor connected across a voltage source is actually drift current as the plates are charged up to the respective battery terminal polarities? Or, a better question is, what IS the current that flows between the battery and the leads of the capacitor to when the plates are charging to their respective polarities (since current is not really flowing through the capacitor and completing a loop) from battery + to battery -?
for displacement current density, the electric flux vector (D.arrow) changes in magnitude, correct?
Thank you!
Great job!
With respect, it is not what you said that I object to. It is what you didn't say.
A moving charge (i.e. a conduction current) establishes a magnetic field.
But a time-varying electric field also establishes a magnetic field by Ampere's circuital law.
And so, from the perspective of the magnetic field, the induced magnetic field doesn't "know" whether it was established by a moving charge or by a time-varying electric field.
To talk about displacement current (the partial derivative of D with respect to t) without talking about the curl of the induced magnetic field is to leave students somewhat in the dark. The "stretching" of the mind regarding what a current is comes down to Ampere's Law: If the curl of a magnetic field is not zero, you are dealing with some kind of current. It may be conduction current (J = sigma*E) or displacement current (partial derivative of D with respect to t). Either way, you have a non-zero curl of the magnetic flux density. And that is as good a general definition of current as any.
To understand displacement current, students need to understand curl, Stoke's theorem, and Ampere's generalized circuital law.
Thank god for your comment only one who gets it up in here.
thanks a lot!!!!
is there any relation between displacement current and the current of the voltage source. what you are saying is displacement current would be the same whether my voltage source is 12v 9A or 12v 1mA
4:07 Is the top equation where voltage is equal to the Line Integral of the Electric Field supposed to have a negative? I guess using the magnitude of the Field changes that?
Can the current flow through the capacitor even if the current is DC?? I thought that impedance becomes infinite for capacitors when frequency is zero. Can anyone explain about my question please?
Yes. Using AC math, we know at time = infinity the impedance of a capacitor becomes zero. But with DC math, we can see what happens before that! Going from frequency domain to time domain might involve fourier analysis. Current will flow through the circuit and a displacement current will appear and exponentially decay to zero at time = infinity.
Darklink9110 almost.....except the current through the wire is also a displacement current.
In case you're having trouble with that, ask yourself how quickly that capacitor charges. Then remind yourself how quickly electrons "flow" in a conductor. Correct, electrons do not"flow" anywhere near the speed of light.
This video presents a very naive discussion of displacement current......flow of electrons and current meters only have meaning when electromagnetic propagation is being slowed down *considerably* by the distributed resistance of a transmission line or other circuit elements. With a voltage connected directly to a capacitor as drawn, there is only one conduction current and that is zero......it is all an instantaneous displacement current caused by an electromagnetic field traveling at whatever the speed of light is in that medium.
As drawn, at no time is there ever any measurable current which is dictated by the speed of electrons in a conductor.....good luck finding those ammeters which apparently have a measurement time close to the speed of light!
As drawn, the operation of the entire circuit is dictated by electromagnetic wave propagation and at no time by "flow" of electrons....ie. there is no "conduction current" that can ever been measured by those ammeters in the circuit drawn (other than zero at dc)
Dear powerpoint professor....if you're going to segway into displacement current like this, please just stick a resistor in your conduction current circuit and stop confusing another generation of engineers.
Just a resistor would show you really know the difference.
Simple answer: Impedance becomes infinity when the frequency is zero, but that does not happen instantenously. Time depends on the capacitance of the capacitor.
voltage should be negative of integral of E and dl @ 4:51
You stopped short of explaining the mechanism of displacement current flow through a capacitor in a vacuum.
Without an explanation for that, doesn't it seem like an incomplete model?
Yes, I agree. Everything in this video was clear, but I was really hoping for an explanation of the above. I also found this video helpful: czcams.com/video/zTuLT8zrDnI/video.html
Hey, I believe the same question has been bogging my mind for the last two days. I think this post pretty much cleared the relationship between change in electric flux and the resulting conduction current equaling to the displacement current: physics.stackexchange.com/questions/83715/what-constitutes-displacement-current
I believe that the charge of an electron is not really concentrated in the place where we say that the electron is located, but its “carrier” is the whole field of the electron. Its highest density (D vector) is around the electron, but then continues to "infinity". Therefore, in Maxwell's equations in differential form, ie valid for the element of continuous space, we do not use the expression dQ/dt, but dD/dt (partial derivative). Vector D represents the charge density per considered spatial element, although the electrons themselves may be far away in the metal electrodes. dD/dt is then the density of the Maxwell displacement current flowing through this dielectric element.
SAME wonder that we make in >>>>how votage can be buildt across a coil it is just a wire then we learn that voltage is not because the resistevity of the wrie rather it is due to current struglle to build the megnatic field
in the cam the same wonder bulit again how should current cross the cap while its an open circuit same solution the ekectric field is the media by which the current travels this is the most intuitive thing if you get the coil you get the cap
Shit. This is my second time watching this video. At first I didn't really get what displacement current is. In the capacitor example, I was bent on the idea that when the capacitor is charging, charge moves from one plate to another, that's it, end of story. But I think I get it now: That in order to satisfy circuit theory, Kirchoff's current at a node, we must define a displacement current, such that the current leaving one plate of the capacitor, is equal to the rate of change of the electric field, which is "the current entering the plate". But, now that I think about it, displacement current in this scenario is just another way of saying i = c dv/dt, just in terms of the electric field, hmm...
Nobody said this stuff was gong to be easy
Mby we dont understand current at all.. mby its compleatly different story. I believe there is much more simple things to meshure and it has strong ties with everything. But im just a regular fool. I know a little and i would like to know more but info doesnt suck up for me if info is not in the right order as 1-100. Haja.. go humans go!
so we can say that there is current flow ! :)
And that is the explanation to the misterious Tesla Hairpin Circuit and what layman describe as cold electricity or scalar waves. Mystery solved.
Displacement current through the cap. ? seems like no permanent break down of the dielectric if charges move through it !!! you can't even say that whether physically there is moving charge or not this is how we define it !! as engineers it makes no sense at all you're just messing ...... Engineers apply science after full understanding of the concepts not creating it ... please if you have reasonable explanation try to do it but you have done is a mess
If current is flowing through the capacitor ("ridiculous remark"), then throw the capacitor away!
frequency dependent of course.
why do profs think power points are good. you should be doing every lecture by hand. if you use power point, no one remembers anything. it's useless for math, and you're a terrible prof if you use ppt.
So-What-You're-Really-Saying Is-When-You 'Discharge'-a-CAPACITOR You-Create a Momentary-Magnetic-FIELD!!!??? >(*u^)< Should-Be 'Testable' Using Iron-Filings.