Professor, why doesn't the self-inductor have any electric field of it is made of superconducting material? And why does the resistor have an electric field? I have watched all your prior lectures and haven't been able to understand this. The last equations that we ever study about electric field is for the relation with p.d. (V = -Integral(E.dl)). Why doesn't superconducting material have any electric field within it?
@@lecturesbywalterlewin.they9259 Thank you a bundle professor! I haven't been understanding this, given that it had such a simple reason! If I may, can I ask a follow-up question? So, now because the resistor has resistance R, and V=IR, V is non-zero, hence E must be non-zero too. But, since V = -Integral(E.dl), does the value depend on the length dl of the resistor?
@@lecturesbywalterlewin.they9259 Hope you are well Professor b/c I haven't been for the last few days... 🤒 🤧 -But I'm getting better! I'm a bit flummoxed myself on inductors, so could you please tell me if I am correct in my explanation below: In the inductor, we do have Enet=Σσ/ε₀. Therefore if Enet=0, then the net charge density is zero. Whatever (fixed) A is chosen as , we have the net charge & net electric flux φ is zero. Enet=ΣQ/ε₀A=φ/A =0 Because of the shape of the coil, there are as many charges in one direction at any point inside as the opposite, therefore all E-fields in the coil cancel out along the wire, but the E-fields don't cancel facing out or in, so depending on the charge considered, it will experience an electric force either in or out of a loop. If you start by considering how the magnetic fields superimpose on portions of the coil, you get the same result but we call that force "magnetic". Either way, if the resulting force on a charge in the wire of the inductor is normal to the direction of the velocity of the charge, then there can be no work done on the charge along the wire. In fact, the direction of the force on a free charge carrier is outwards, so the charge loses its bond with the wire and may escape the wire! If it did that,then it could also come back down and cause pressure on other charge carriers of the same sign, and this would cause fluctuations in potential along the wire due to the charge density wave created by the rising and falling charge. But eventually everything tries to equalise in the circuit and that means potentials at either end of the inductor will try to balance out so that the current goes to a minimum value due to the inertia of charge carriers and Newton's laws of motion. The charge carriers can still flow through the coil without any net force along the wire, as long as when the charges are outside the wire, the electric forces conspire to draw them back into the wire and crash into other charges. Technically there is no current in the coil because drift velocity is a change in velocity, but there can still be a flow of charge in some direction due to constant velocity. Perhaps the charges could be bouncing up and down normal to the wire, but the component of velocity along the wire is constant❔ 🤔
@@lecturesbywalterlewin.they9259 I have already watched your lectures. But I couldn't find a thing like "there is an E-field in the AC power supply". But what is the difference between inductor and AC power supply? their working principle is much similar. and both of them's E-fields are circular(creates a closed loop in the circuit) and if there is no electric field inside the inductor, than there shouldn't be any E-field inside the AC power supply. Please tell me the truth if I said a wrong thing. thank you
@@ugursoydan8187 yes there is an E-field inside a battery and inside a power supply, and NO there cannot be any E-field inside an ideal inductor which is a coil made of superconductive wire. END of story - watch my lectures.
When I was creating the differential equation, I got the same thing on the left side but my right side was EMF/L
Professor, why doesn't the self-inductor have any electric field of it is made of superconducting material? And why does the resistor have an electric field? I have watched all your prior lectures and haven't been able to understand this. The last equations that we ever study about electric field is for the relation with p.d. (V = -Integral(E.dl)). Why doesn't superconducting material have any electric field within it?
V=IR if R is zero V must be zero but if V is zero E must be zero. Yet I can then be anything.
@@lecturesbywalterlewin.they9259 Thank you a bundle professor! I haven't been understanding this, given that it had such a simple reason! If I may, can I ask a follow-up question?
So, now because the resistor has resistance R, and V=IR, V is non-zero, hence E must be non-zero too. But, since V = -Integral(E.dl), does the value depend on the length dl of the resistor?
@@lecturesbywalterlewin.they9259
Hope you are well Professor b/c I haven't been for the last few days... 🤒 🤧
-But I'm getting better!
I'm a bit flummoxed myself on inductors, so could you please tell me if I am correct in my explanation below:
In the inductor, we do have Enet=Σσ/ε₀.
Therefore if Enet=0, then the net charge density is zero.
Whatever (fixed) A is chosen as , we have the net charge & net electric flux φ is zero.
Enet=ΣQ/ε₀A=φ/A =0
Because of the shape of the coil, there are as many charges in one direction at any point inside as the opposite, therefore all E-fields in the coil cancel out along the wire, but the E-fields don't cancel facing out or in, so depending on the charge considered,
it will experience an electric force either
in or out of a loop.
If you start by considering how the magnetic fields superimpose on portions of the coil, you get the same result but we call that force "magnetic".
Either way, if the resulting force on a charge in the wire of the inductor is normal to the direction of the velocity of the charge, then there can be no work done on the charge along the wire.
In fact, the direction of the force on a free charge carrier is outwards, so the charge loses its bond with the wire and may escape the wire!
If it did that,then it could also come back down and cause pressure on other charge carriers of the same sign, and this would cause fluctuations in potential along the wire due to the charge density wave created by the rising and falling charge.
But eventually everything tries to equalise in the circuit and that means potentials at either end of the inductor will try to balance out so that the current goes to a minimum value due to the inertia of charge carriers and Newton's laws of motion.
The charge carriers can still flow through the coil without any net force along the wire, as long as when the charges are outside the wire, the electric forces conspire to draw them back into the wire and crash into other charges.
Technically there is no current in the coil because drift velocity is a change in velocity, but there can still be a flow of charge in some direction due to constant velocity.
Perhaps the charges could be bouncing up and down normal to the wire, but the component of velocity along the wire is constant❔ 🤔
Great video!
One thing I did not understand is that what do the dots on the top mean at 5:05?
x-dot is a shorthand notation for dx/dt
x-double dot is a sh notation for d2x/dt^2
Lectures by Walter Lewin. They will make you ♥ Physics.
Oh! Thank you so much, sir.
Should we divide by L when forming the differential equation? The units don't work out
Sheikh Abdur Raheem Ali I got the same thing. Should be equal to EMF/L
how come there is an electric field inside the AC power supply and there is no electric field inside the inductor?
watch my 8.02 lectures
@@lecturesbywalterlewin.they9259 I have already watched your lectures. But I couldn't find a thing like "there is an E-field in the AC power supply". But what is the difference between inductor and AC power supply? their working principle is much similar. and both of them's E-fields are circular(creates a closed loop in the circuit) and if there is no electric field inside the inductor, than there shouldn't be any E-field inside the AC power supply. Please tell me the truth if I said a wrong thing. thank you
@@ugursoydan8187 yes there is an E-field inside a battery and inside a power supply, and NO there cannot be any E-field inside an ideal inductor which is a coil made of superconductive wire. END of story - watch my lectures.