WOW! Loved this mini-lecture Professor! Thank you for clearing the difference between Faraday's laws and KVL. I request you to please keep uploading this type of mini-lectures. Really enjoyed a lot. One last thig to say..... those real life examples (torch and radio) are really amazing!
Hello Hello Hello Professor ❤Walter! I am very grateful to you for changing the way I view the world and understand physics. I will be giving the JEE and would be thankful for your well wishes
Thanks for explaining again sir. I understand a little bit better than before. Maybe. I like to think of a self inductor as a component where the voltage falls over, even if the resistance is zero. That's a simplified view and I'm aware of that but it allows for a simple analysis of circuits where KVL hold's. There are times when this simplified view is not enough, typically when the electromagnetic field of a self inductor interferes with other component's or even other devices. It can be very painfull if we engineer something and that is causing a problem.
Good Morning professor Lewin, you are the best teacher that each student can desire to meet. Congratulations for all your job eng. Paolo Massa from Italy
These mini lectures are priceless professor. They can help us mortals to catch concepts that may have taken a lifetime or more🙌🙏 Please look after your health professor - Omega3's, Vitamin D(requires Magnesium(Magnesium Citrate)), Astaxanthin, Vitamin B's, Calcium(very important for the nervous system) and Vitamin C - I think these are most important. Siim Land did a video a few days ago on what he takes if you want to look at it prof... like Siim says at the end of his video -stay optimized stay empowered😉⚡
Excellent information Sir. It was never told by any Physics teacher and most books also don't explain it. In circuit theory, Simple KVL gives same answer. But how we get different reading in different directions for same potential points in physical sense? Thanks and Regards
When there is an induced EMF, then KVL does NOT give the same answer as Faraday. *Potential diff is not well defined anymore whe there is a induced EMF. The integral of E do dL then depends on the path.*
use google - EM waves are formed by electric and magnetic fields but are not deflected by them, and also they can be deflected by gravitational fields. Light (electromagnetic wave) has an electric and a magnetic field and should thus deflect a compass needle during daytime.
Tomorrow 4th April which is the beginning of the smiles of thousands and cries of around hundred thousand of Indian 12 grade students hope you know what am taking about
@@lecturesbywalterlewin.they9259 thanks for the reply sir ,,,, Well I was about to say that the JEE MAINS phase 2 are starting from tomorrow which is like an earthquake to most of the students 😅😅
@@luiesherosaki4797 😅 , You should Post the same Statement on or Before 26th May, He may respond Better then this than/ Aware of! Hopefully You got it :D
Engineers use KVL because it is handy tool for solving loop currents. Engineering teachers never even mention that Faraday's Law is the underlying basis for KVL. The confusion shows that engineers are not physicists. Physicists show what's possible, engineers build.
@@lecturesbywalterlewin.they9259 Engineers love shortcuts, so they made KVL work on transformers too. SInce Faraday's Law always work, transformers can just be represented as an element in a circuit. Then power engineers invented another shortcut called per-unit calculation where transformers disappear in the calculation for voltages, currents, and power. So thanks to Faraday's Law, it made some shortcuts possible.
@@MrKinyodude I am glad to know that engineers had to jump through a few hoops to still get the right answer. Physicists, who would use Faraday's Law, would not have to jump through any hoop and they would never have any doubts about their correct solution.
Sir i got inspired by you in physics and you make this intrest more and more always thanks for that my respected inspirational professor and love ❤ from india
Hi Walter My comment is not about the applicability of KVL to the circuit , however there is certainly an electric field along the wire of the self inductor , by the definition of the electric field there is an electric field along the wire , because there are charges there experiencing a force and that is the definition of an electric field.
There is NO E-field inside a suerconductor. *Thus the intergal of E dot dL through the superconducting wire of the inductor from one end to the other is always ZERO!*
@@lecturesbywalterlewin.they9259 Regardless of the low or Zero resistance the electric field is there E = F/q . Charges along the wire are experiencing a force along the wire and so there is by definition an electric field along the wire. Ohmic resistance along a wire is not a requirement for an electric field to be located along a wire.
@@woodcoast5026 There is NO E-field inside a suerconductor. *Thus the intergal of E dot dL through the superconducting wire of the inductor from one end to the other is always ZERO!* End of story
Only when you consider a real conductor with finite conductivity there will be a tiny electric field inside the inductor. A field compatible with Ohm's law in its local form j = sigma E. In the case of a perfect conductor sigma is zero, so the electric field goes to zero. The surface charge that makes the field zero INSIDE the perfectly conducting inductor (or very small inside a real conductor) are also responsible for the nonzero field outside the inductor. This field outside is what makes a voltage appear in the space between the terminals and between turns (but only for paths that form, with the conductor, a one or more loops around the changing magnetic flux).
Professor, I completely understand the explanation but I always had one big question, if there cannot be an electric field in the coil (= ideal conductor), how is application of Faraday's law in differential form explained? Curl(E) = -dB/dt, if the magnetic field through in the space through/around the coil is changing, this laws says that an electric field has to rotate in the plane perpendicular to the changing magnetic field. This electric field is passing through the loops of the coil, what is opposing this field to make the electric field in the ideal coil zero?
you misinterprete Maxwell's eqs. A current can flow through a super conductor. That's what the accelartors in Geneva are all a bout. But no E-field can exist in a super conductor as it has no ohmic resitance.
@@lecturesbywalterlewin.they9259 Thanks for your answer, I still don't see the misinterpretation in curl(E) = -dB/dt... Where does the induced electric field constitute itself?
Prof. Lewin, I do not at all doubt your explanation of the circuit analysis of Faraday's law, but I am interested in how the ambiguity with KVL arises. I pose this question: Suppose we have only a battery and a switch, not even a circuit. Then the point A, which is on the far side of the switch from the battery, when the switch is open has zero potential. But when the switch is closed, point A, according to convention, has a potential of +V, the same potential as the + terminal of the battery. Is this not also the case if we insert the battery and switch into the inductive circuit you have shown?
Apply the closed loop integral on any closed loop. what you are suggesting are no closed loops. KVL only works if there is no induced EMF. Faraday always works also in cases that Ldi/dt = 0.
@@lecturesbywalterlewin.they9259 Thank you for your reply. I only mentioned the isolation of the battery and switch from the circuit to establish the voltage in that case, then to reinsert it as you have it and enquire if the voltage at point A is different in the closed circuit case. I realize the potential is a varying thing when there is an inductance in the circuit, just wondering how it changes at A as the switch is closed. I have no partiality to KVL at all in this case. By the way, I was most impressed with your demonstration in class of the different readings on different sides of the parallel resistors.
@@jackbidnik9642 Watch my video again; I cover (also in Lectire 2) what happens when you close the switch. I even draw pictures how the current changes, depending on the values of L.
Hello professor hope this comment finds you well there and I wanted to ask that whether electric charge is an extensive property or intensive property and how much appropriate this classification would be?
Good Morning sir 🙏.. I am Avanish Singh moving in class 11 as an jee aspirant . I am so happy and excited but I want to join offline coaching and my family doesn't agree because of economical problem. Sir I request you to help me. Sir please help me otherwise my IIT dream will broke. Sir please help me as much you can. I will so grate full to you in my whole lovely life. 🙏🙏 or tell me about some way to overcome this problem.
Watch all my 94 MIT course lectures. Start with 8.01, then 8.02, then 8.03. Do all the homework and take all my exams. *I guarantee you that you will then do very well on the Physics portion of any freshman college or JEE exam* You will find all information you need on this channel in three playlists "Homework, Exam, SolutionsY & Lecture Notes". 8.01 & 8.02 will each take about 200 hours, 8.03 about 250 hours.
Prof my doubt is regarding ur previous lectures at MIT. Back in 801x while you were teaching mechanical physics u took certain uncertainties in ur problems . How were u so certain of ur uncertainties like how did u assume the uncertainties like when ball hit a floor the uncertainty would be about 5 milliseconds in time. That part is a bit confusing 😅😅.
Sir please read my question If we connect a wire of zero resistance across a battery with internal resistance zero Will current flow in the wire as all points on the wire will have same potential. ,?
Taking by your name, I'll issume you're a 10th/11th(to be) grader, here are some things you can consider following 1. Concept, learn it, there's no alternative. 2. Formula derivation, wherever possible, get the hold of how the formula is derived, it will increase the number of sums you can solve. 3. Don't take breaks when you're tired but schedule the breaks and stick to it firmly (even if you wanna continue studying, take the 5 min break)
I also work with Faradays law, but in contrast of you i imagine that under certain conditions there is and must be an E-field in a coil. If you have AC voltage, the resistance of an ideal coil is not zero, it is w * L. The contribution to the E-field from Faraday law - L * di/dt comes from the coil with the inductance L. Depending on whether the magnet field in the coil is increasing or decreasing, the E-field of the coil can support or counteract the E-field of the powersupply. If you think, that there is no E-Field in a coil, how would you explain, that if there is a time changing B-field inside a coil, in one moment the left side of the coil is negative charged and the right side positive and some time later the left side of the coil is positive charged and the right side negative ? That is only possible, if there is an E-field in the coil, which accelerates and decelerates the electrons, so that they move from one side of the coil to the other side and back. A simple situation to demonstrate, that there can be an E-field in a superconductor is: A 1m long cylinder with 1mm diameter in direction of the y-Axis is moved with a velocity v in direction of the x-axis and there is a B-field in direction of z-Axis. Then you will get a voltage between the endpoints of the wire and you can calculate the E-field in this wire with the equation q*E = q*v*B. You can watch my video (and the following lectures for the induction law). czcams.com/video/J7WXOvQOK9E/video.html
This idea for the derivation of the induction law (if you watch the following videos) comes from my father who unfortunately died 2017 and was also a great physic school teacher. You can also download the software for windows for free.
There is no AC electrical current resistance. *There is no resistance in a superconductor, period.* What the statement means is that you do not lose electrons to heat while transferring electrons through the superconductor.
@@michaelbruning9361 Resistance and reactance are the properties of an electrical circuit that opposes the current. The main difference between reactance and resistance is that *resistance measures the opposition to a flow of current,* whereas reactance measures the opposition to a change in current. *A superconducting inductor has zero resistance*
@@lecturesbywalterlewin.they9259 I never lose electrons to heat (charge is conserved). Electric energy is transfered into heat energy. I agree with you, that a superconductor has no ohm resistance. The correct word is probably reactance. In germany we say also inductive resistance, so i wrote resistance.
Hope electroboom vs walter lewin doesn't start again 😊😊😊😊😊
WOW! Loved this mini-lecture Professor! Thank you for clearing the difference between Faraday's laws and KVL. I request you to please keep uploading this type of mini-lectures. Really enjoyed a lot. One last thig to say..... those real life examples (torch and radio) are really amazing!
A very very imp concept explained!! Thankyou for this eye opening video!!
Thank you very much for shedding light, professor, greetings from Argentina
You made my day today, Professor Lewin. Thank you for this lecture.
Glad to hear that!
Thankyou sir for making a whole video on the question I raised in your thired previous video...Keith norman's solution
Hello Hello Hello Professor ❤Walter! I am very grateful to you for changing the way I view the world and understand physics. I will be giving the JEE and would be thankful for your well wishes
Thanks for explaining again sir. I understand a little bit better than before. Maybe. I like to think of a self inductor as a component where the voltage falls over, even if the resistance is zero. That's a simplified view and I'm aware of that but it allows for a simple analysis of circuits where KVL hold's. There are times when this simplified view is not enough, typically when the electromagnetic field of a self inductor interferes with other component's or even other devices. It can be very painfull if we engineer something and that is causing a problem.
>>>>That's a simplified view and I'm aware of that but it allows for a simple analysis of circuits where KVL hold's.
Good Morning professor Lewin,
you are the best teacher that each student can desire to meet.
Congratulations for all your job
eng. Paolo Massa
from Italy
Wow, thank you
These mini lectures are priceless professor. They can help us mortals to catch concepts that may have taken a lifetime or more🙌🙏
Please look after your health professor - Omega3's, Vitamin D(requires Magnesium(Magnesium Citrate)), Astaxanthin, Vitamin B's, Calcium(very important for the nervous system) and Vitamin C - I think these are most important. Siim Land did a video a few days ago on what he takes if you want to look at it prof... like Siim says at the end of his video -stay optimized stay empowered😉⚡
Very cool lesson.
Glad you liked it!
Excellent information Sir. It was never told by any Physics teacher and most books also don't explain it. In circuit theory, Simple KVL gives same answer. But how we get different reading in different directions for same potential points in physical sense? Thanks and Regards
When there is an induced EMF, then KVL does NOT give the same answer as Faraday. *Potential diff is not well defined anymore whe there is a induced EMF. The integral of E do dL then depends on the path.*
Love From India ❤️❤️❤️❤️
I love your physics videos
SIR, I have a doubt
Can an electromagnetic wave be deflected by a magnetic field ? Explain.
use google - EM waves are formed by electric and magnetic fields but are not deflected by them, and also they can be deflected by gravitational fields. Light (electromagnetic wave) has an electric and a magnetic field and should thus deflect a compass needle during daytime.
@@lecturesbywalterlewin.they9259 thank you sir
Tomorrow 4th April which is the beginning of the smiles of thousands and cries of around hundred thousand of Indian 12 grade students hope you know what am taking about
1897 April 4 (not Febr 4) Hugew Earthquake in India
@@lecturesbywalterlewin.they9259 thanks for the reply sir ,,,,
Well I was about to say that the JEE MAINS phase 2 are starting from tomorrow which is like an earthquake to most of the students 😅😅
@@luiesherosaki4797 😅 , You should Post the same Statement on or Before 26th May, He may respond Better then this than/ Aware of!
Hopefully You got it :D
Engineers use KVL because it is handy tool for solving loop currents. Engineering teachers never even mention that Faraday's Law is the underlying basis for KVL. The confusion shows that engineers are not physicists. Physicists show what's possible, engineers build.
If engineers *always* use KVL then transformers and internet would not exist and planes could not fly. *Luckily the Physicists call the shots!*
@@lecturesbywalterlewin.they9259 Engineers love shortcuts, so they made KVL work on transformers too. SInce Faraday's Law always work, transformers can just be represented as an element in a circuit. Then power engineers invented another shortcut called per-unit calculation where transformers disappear in the calculation for voltages, currents, and power. So thanks to Faraday's Law, it made some shortcuts possible.
@@MrKinyodude I am glad to know that engineers had to jump through a few hoops to still get the right answer. Physicists, who would use Faraday's Law, would not have to jump through any hoop and they would never have any doubts about their correct solution.
After watching the 18 min lecture, I go to the 50 min lecture 16. And now I am going to look-up what is "conservative filed"...
it means curl is zero, in vector analysis sense
Sir i got inspired by you in physics and you make this intrest more and more always thanks for that my respected inspirational professor and love ❤ from india
All the best
Sir why the light is moves forward
Which force push the photons forward???
light has no rest mass but it does have momentum and Enegry. All massless particles (photons) must move with the speed of light (use google).
Dear Mr. Lewin, a Chinese high school student, you made me go from hating physics to loving physics. China's terrible exam-oriented education😢
Hi Walter
My comment is not about the applicability of KVL to the circuit , however there is certainly an electric field along the wire of the self inductor , by the definition of the electric field there is an electric field along the wire , because there are charges there experiencing a force and that is the definition of an electric field.
There is NO E-field inside a suerconductor. *Thus the intergal of E dot dL through the superconducting wire of the inductor from one end to the other is always ZERO!*
@@lecturesbywalterlewin.they9259
Regardless of the low or Zero resistance the electric field is there E = F/q . Charges along the wire are experiencing a force along the wire and so there is by definition an electric field along the wire. Ohmic resistance along a wire is not a requirement for an electric field to be located along a wire.
@@woodcoast5026 There is NO E-field inside a suerconductor. *Thus the intergal of E dot dL through the superconducting wire of the inductor from one end to the other is always ZERO!* End of story
@@lecturesbywalterlewin.they9259 I think you keep getting this from people b/c they do not understand why E=0 in a super conducting inductor.
Only when you consider a real conductor with finite conductivity there will be a tiny electric field inside the inductor. A field compatible with Ohm's law in its local form j = sigma E.
In the case of a perfect conductor sigma is zero, so the electric field goes to zero.
The surface charge that makes the field zero INSIDE the perfectly conducting inductor (or very small inside a real conductor) are also responsible for the nonzero field outside the inductor. This field outside is what makes a voltage appear in the space between the terminals and between turns (but only for paths that form, with the conductor, a one or more loops around the changing magnetic flux).
Professor, I completely understand the explanation but I always had one big question, if there cannot be an electric field in the coil (= ideal conductor), how is application of Faraday's law in differential form explained?
Curl(E) = -dB/dt, if the magnetic field through in the space through/around the coil is changing, this laws says that an electric field has to rotate in the plane perpendicular to the changing magnetic field. This electric field is passing through the loops of the coil, what is opposing this field to make the electric field in the ideal coil zero?
you misinterprete Maxwell's eqs. A current can flow through a super conductor. That's what the accelartors in Geneva are all a bout. But no E-field can exist in a super conductor as it has no ohmic resitance.
@@lecturesbywalterlewin.they9259 Thanks for your answer, I still don't see the misinterpretation in curl(E) = -dB/dt... Where does the induced electric field constitute itself?
Prof. Lewin, I do not at all doubt your explanation of the circuit analysis of Faraday's law, but I am interested in how the ambiguity with KVL arises. I pose this question: Suppose we have only a battery and a switch, not even a circuit. Then the point A, which is on the far side of the switch from the battery, when the switch is open has zero potential. But when the switch is closed, point A, according to convention, has a potential of +V, the same potential as the + terminal of the battery. Is this not also the case if we insert the battery and switch into the inductive circuit you have shown?
Apply the closed loop integral on any closed loop. what you are suggesting are no closed loops. KVL only works if there is no induced EMF. Faraday always works also in cases that Ldi/dt = 0.
@@lecturesbywalterlewin.they9259 Thank you for your reply. I only mentioned the isolation of the battery and switch from the circuit to establish the voltage in that case, then to reinsert it as you have it and enquire if the voltage at point A is different in the closed circuit case. I realize the potential is a varying thing when there is an inductance in the circuit, just wondering how it changes at A as the switch is closed. I have no partiality to KVL at all in this case. By the way, I was most impressed with your demonstration in class of the different readings on different sides of the parallel resistors.
@@jackbidnik9642 Watch my video again; I cover (also in Lectire 2) what happens when you close the switch. I even draw pictures how the current changes, depending on the values of L.
Hello professor hope this comment finds you well there and I wanted to ask that whether electric charge is an extensive property or intensive property and how much appropriate this classification would be?
question unclear - use google
Sir iam your biggest fan from india im currently 16 years old watching you from 1 year can you tell me how can i become like you
I'm from class 9th sir...and I want to know about the topic ENTROPY of Thermodynamics....
use google
Holy skibidi!
Good Morning sir 🙏..
I am Avanish Singh moving in class 11 as an jee aspirant . I am so happy and excited but I want to join offline coaching and my family doesn't agree because of economical problem. Sir I request you to help me. Sir please help me otherwise my IIT dream will broke. Sir please help me as much you can. I will so grate full to you in my whole lovely life. 🙏🙏 or tell me about some way to overcome this problem.
Watch all my 94 MIT course lectures. Start with 8.01, then 8.02, then 8.03. Do all the homework and take all my exams. *I guarantee you that you will then do very well on the Physics portion of any freshman college or JEE exam* You will find all information you need on this channel in three playlists "Homework, Exam, SolutionsY & Lecture Notes".
8.01 & 8.02 will each take about 200 hours, 8.03 about 250 hours.
But sir for chemistry and maths??
I think alakh panday sir will help me if you help me. For offline course at my nearest center varanasi i.e. BHU.
Prof my doubt is regarding ur previous lectures at MIT. Back in 801x while you were teaching mechanical physics u took certain uncertainties in ur problems . How were u so certain of ur uncertainties like how did u assume the uncertainties like when ball hit a floor the uncertainty would be about 5 milliseconds in time. That part is a bit confusing 😅😅.
czcams.com/video/I4cXejTr_3c/video.html
Thanks prof
A warning to these climate people that think batteries can run the world.
Sir please read my question
If we connect a wire of zero resistance across a battery with internal resistance zero
Will current flow in the wire as all points on the wire will have same potential. ,?
This is one of my Physics Problems - go for it and also read the solution. Current will flow but NOT through the wire
Love the music. Wonder who was the artist, and what was the title and year😂
1st from India please reply me I wanna know how to focus on studies and my weakest subject is physics please help me sir
eat yogurt every day but *never on Fridays* That worked well for Einstein and also for me.
😂@@lecturesbywalterlewin.they9259
@@lecturesbywalterlewin.they9259😅
Taking by your name, I'll issume you're a 10th/11th(to be) grader, here are some things you can consider following
1. Concept, learn it, there's no alternative.
2. Formula derivation, wherever possible, get the hold of how the formula is derived, it will increase the number of sums you can solve.
3. Don't take breaks when you're tired but schedule the breaks and stick to it firmly (even if you wanna continue studying, take the 5 min break)
I also work with Faradays law, but in contrast of you i imagine that under certain conditions there is and must be an E-field in a coil.
If you have AC voltage, the resistance of an ideal coil is not zero, it is w * L.
The contribution to the E-field from Faraday law - L * di/dt comes from the coil with the inductance L.
Depending on whether the magnet field in the coil is increasing or decreasing, the E-field of the coil can support or counteract the E-field of the powersupply.
If you think, that there is no E-Field in a coil, how would you explain, that if there is a time changing B-field inside a coil, in one moment the left side of the coil is negative charged and the right side positive and some time later the left side of the coil is positive charged and the right side negative ?
That is only possible, if there is an E-field in the coil, which accelerates and decelerates the electrons, so that they move from one side of the coil to the other side and back.
A simple situation to demonstrate, that there can be an E-field in a superconductor is:
A 1m long cylinder with 1mm diameter in direction of the y-Axis is moved with a velocity v in direction of the x-axis and there is a B-field in direction of z-Axis.
Then you will get a voltage between the endpoints of the wire and you can calculate the E-field in this wire with the equation q*E = q*v*B.
You can watch my video (and the following lectures for the induction law).
czcams.com/video/J7WXOvQOK9E/video.html
This idea for the derivation of the induction law (if you watch the following videos) comes from my father who unfortunately died 2017 and was also a great physic school teacher.
You can also download the software for windows for free.
Definition of IDEAL coil is ZERO ohmic resistance!
There is no AC electrical current resistance. *There is no resistance in a superconductor, period.* What the statement means is that you do not lose electrons to heat while transferring electrons through the superconductor.
@@michaelbruning9361 Resistance and reactance are the properties of an electrical circuit that opposes the current. The main difference between reactance and resistance is that *resistance measures the opposition to a flow of current,* whereas reactance measures the opposition to a change in current. *A superconducting inductor has zero resistance*
@@lecturesbywalterlewin.they9259 I never lose electrons to heat (charge is conserved). Electric energy is transfered into heat energy. I agree with you, that a superconductor has no ohm resistance. The correct word is probably reactance. In germany we say also inductive resistance, so i wrote resistance.
This video is sponsored by.. FARADAY'S LAW!
yes I got $10 thousand from Maxwell
Hello sir
Hi sir
Buddha statue spotted in the background
Well, I don't know, - it's not convincing...
poor you - if you still don't get it, then you never will. These are the consequences of Maxwell's eqs.
@@lecturesbywalterlewin.they9259 smile, professor! ♥