Professor I am studying physics again. I studied it in high school and graduation and didn't really understand anything. I have been constantly watching your videos and it has indeed changed the way I used to perceive Physics. Now it is so beautiful that if I am not well, i watch these lectures or study Physics. Huge respect for you. I wish I could meet you someday.
This website contains all my 94 course lectures (8.01, 8.02 and 8.03) with improved resolution. They also include all my homework problem sets, my exams and the solutions. Also included are lecture notes and 143 short videos in which I discuss basic problems. ENJOY!
Lectures by Walter Lewin. They will make you ♥ Physics. Sir you say that a changing magnetic flux linked with the coil produce current in the coil. Sir classical physics says that it is due to the inertia of the coil. The coil does not want to change the magnetic flux linked with it. That's why it produced current to oppose the changing magnetic flux. Sir how the reason given by the classical physics is not correct.
Faraday's Law is classical Physics and *it is 100% correct!!!!* It runs our entire economy. There can not be any confusion. If this is not enough for you, consult google.
I'm so glad I found your videos Professor. I'm always trying to find things to learn more about these kinds of subjects and your lectures are better than anything that I've been able to find. Thank you so much!
Thanks to this lecture (part about eddy currents and mag braking) I finally understand why a magnet falls so slowly when we let it fall through a hollow conducting cylinder :)
All of your lectures are fascinating and dense with information. I especially enjoy 8.02, but would recommend all of your lectures as required learning for anyone interested in physics!
The lecture was remarkable, even today Micheal Faraday is not alive, but by watching this lecture and all experiments that you have done, I found Micheal Faraday is still there.. especially experiments helped me a lot.. thank you.
I can not appreciate your lectures enough. I'm doing my Master's in Germany and working on Magnetic field influence on Electrochemical process. I was interested in your take on the Magnetic field effect on a charge carrier of an ion conductor (or electrolytes). Thank you! God Bless you, Sir.
Interesting to note that the shaft in the Indian Point power station that I visited that drives the dynamo is .8m in diameter and about 60m long and made of solid steel. The torque on the shaft causes the shaft to twist 270 degrees our of true when generating electricity! Real work is happening! Thanks for the lectures
dear professor you are the best person I have ever heard,i can understand more from 10min than any one I ever heard not MIT must have lost there mind, you're an inspiration you are my hero you give me inspiration and give me great ideals in anti gravity,people call me a nut job but I have some success in small experiments (it's not really gravity that we are defeating) the earth is a big magnet 😁
I am 60 now. And addicted to Walter's lectures and binge watching all his videos. I loved the Dynamo demo in this video. In my younger days I used to see small Dynamo that can be attached to the backwheel of the Bicycle. A light bulb in the front connected to the dynamo serves as light source during night time riding in the dark. When dynamo rotator attaches to the wheel it's a bit more difficult to pedal the Bicycle wheel (Lenz's law).
Hello professor Walter. Im a Physics entusiast, i dont have any grade or college education. Im just making this coment to thank you. You thought me everything i know about Physics!
When the power grid becomes overloaded, generators slow down slightly (frequency drops from 60Hz) and motors slow down and do less work over time. Generation and load are balanced by AC line frequency. Underfrequency relays automatically drop load at about 59.5Hz to prevent generator damage and customer damage. When you turn on a light bulb in Boston, the frequency drops a very small amount on the entire east coast until generation speeds up a very small amount to return toward 60Hz. Time keeping is corrected after midnight when load drops and there is excess generation available. The amount of power a generator adds to the power grid is controlled by it's generating turbine speed (frequency) and not by voltage as most people expect. I really doubt that Walter Lewin camping flashlight (27:46) generates 120 Watts. More likely 1 Watt. or less. Most people can generate about 60 Watts with a real struggle on a bicycle. Thanks Walter, I do love physics and your lectures.
>>>I really doubt that Walter Lewin camping flashlight (27:46) generates 120 Watts. >>> *what made you think so??? I never said that.* Watch the video again. My dynamo would probably produce 5-10 W if I work very hard!.
(27:46) "This is a 120 Watt light bulb and I keep it going all the time". Either way, you have a great way of personally connecting with your students and that was one example. Thank you.
Thank you Prof. Lewin for your fabulous lectures! In your demonstration with the copper pendulum being slowed by the solenoids, you used power conservation arguments to explain the dampening. I am having trouble picturing how the dampening force (the direction especially) is created using F=qvXB and Faraday's law. Could you please comment? Thank you in advance.
+Wallace Yang Eddy currents are not easy to model. Yet, it is clear that they consume energy (ohmic heat). Where does that energy come from? It has to be gravitational potential energy since that's the only energy source available. If you moved a metal plate through a magnetic field you will have to do work. You will have to push! Your work emerges as heat in the metal produced by eddy currents. There is a q(vXB) force on your metal that you have to overcome. You move the metal with velocity v. The free electrons in the conductor start moving.
Belated happy teacher's day sir!! Sorry its too late!! (In India we celebrate it on 5th Sept.) Thank you very much sir for making us love physics as you do!!!😊😊🙏😀
If only i had a lecturer with this high quality, i would be a physicist.. unfortunately i only got formulas in learning physics just to calculate without knowing the concepts... and it makes physics is a mystery and boring.. thank you very much Prof, u rock!
Awesome lecture on magnetic braking. I'm pretty sure metals like aluminum that respond with such vigor to electromagnets do so, because they produce a greater number of eddies than copper, and it possible an alloy out there somewhere would be even more responsive. I was working on a problem in my head using magnetic braking, and thinking I can't have it correct. All that kinetic energy coming to a halt, but where's the equalization. Then you said it generates heat, and the balance of the universe was once again as it should be. I get focused on something and over look a basic function of objects doing work.
Dear Sir, if any student any where in the world doesn't understand your 8.01, 8.02 and 8.03 not grade pass/fail but alteast general ideas/concepts, they are not eligible to pursue their engineering .. that should be made global law.. as without these basics no research could be done.. by those graduating students.. take a bow Sir from india.. and in any univestity engineering disciple.. this should be order of course structre. 1) math series all from calculus to differential equeations .. 2) your phyiscs/nature series.. ........ rest all doesnt matter and student can fully appreciate and understand any discipline..
I strongly suspect my teachers themselves didn’t understand what they were teaching. Just regurgitating what’s in text books is not teaching and that’s what they did. Everything was geared towards doing well in exams and not stimulating student interest. This is a completely different approach!
Prof. You rotate the loop in x axis which the magnetic flux would not change. You should have rotated in y Axis in order angle teta and also flux to change.
Hi! Thanks for the videos. I had a question: in the last example, the one of the loop that has a hole, how can the current jump over the gap?? Why is there current going through the gap? Thank you!!
Great thanks sir I want to participate in Ipho this year or next and Ur lectures are really helpful But I have a question: When U talked about the motional EMF u just took the case of a rod what will be the situation if had a conducting sphere or any other shape I hope u answer and thanks!
Sir, at 5:20 how will you be able to rotate that loop with a constant angular velocity? If you were applying a constant torque , the induced current will develope an opposing torque which is also sinusoidal and therefore the resultant torque applied to the loop is not zero then , how the angular velocity will be constant ?
Good afternoon sir, you lectures have helped me a lot on understanding the subject, l am experiments with making a generator , but could not produce electricity, l suppose l should keep rotating a lot more. , Which l will try again
When you were finding direction of Lorentz force on the conductor in case of Magnetic breaking, there were 2 possible directions of Lorentz force......if we consider the solid disc perpendicular to the page then once current will come out of page and once current will go into page but you found Lorentz force for one direction only....(38:02)????
Lorentz force will reverse when dphi/dt changes from + to minus. In both cases heat is produced inside the disc. Thus the disc will slow down as it enters the B-field and also as it leaves the B-field. That's called magnetic breaking.
When discussing the eddy currents, you say the current must pass through the air, but why doesn't the induced current just travel on the surface of the conductor (at 39:24)? Any help would be greatly appreciated!
Since childhood, I have been worried about the question, how can they not understand the obvious truth, which is that the area of the contour has nothing to do with the emergence of EMF? There is no way to create a time-varying magnetic field so that the magnetic induction vector simply "sticks" into the circuit, as is always shown in lectures. The magnetic lines of force ALWAYS enter the circuit through its borders from the outside. And, thus, there is a PROCESS of crossing the conductor of the contour by the magnetic lines of force. Consideration of this process by means of the contour area is a mathematical abstraction that has nothing to do with the physics of the process. Of course, everything converges numerically, because the area of the contour is directly related to the perimeter of this contour, but PHYSICALLY the process occurs in a completely different way. To understand WHY Maxwell wrote it down in this form, you should read Maxwell's treatise on electricity and magnetism and pay attention to the MODEL from which his equations are derived. You can do a very simple experiment. For the case when the area of the circuit changes, the current will be proportional to the number of moving conductors. That is, if you put 2, 3 or 5 conductors at a short distance on the open edge of the circuit and move them all together to the right or left, the current will be approximately 2, 3 or 5 times more than with one conductor. Since the moving conductors will influence each other as well, the ratio is inaccurate. Of course, the magnetic field must be sufficiently uniform along the trajectory. Also, if you move the entire circuit in a uniform magnetic field, but create unequal conditions for the front and rear conductors (cover one of them with one or another metal, choose different materials, etc.), EMF and current will also arise. Moreover, it follows from Faraday's law that no PROCESSES take place in an open loop! BUT! Try to get close to the output terminals of the idle step-up transformer! You will be shocked even BEFORE you touch the terminals! HOW did the transformer know that you approached ?!
I am trying to visualize the geometry of the open surface with a closed loop in Faraday's law, and what I have done is using a helicoid frame (shorturl.at/cxSW3) to match the relationship between the open surface and its associated closed loop. However, I still can not make it. For example, In this helicoid mentioned above, the surfaces which extend from different portions of the frame seem to intersect. Does that matter? Or I went to wrong direction to approach this problem? Any help is appreciated, thanks a lot.
Sir you said that in ac circuit(making a bulb glow) bulb still glows(as heating effect of tungsten still remains) even when current is 0 Sir but what happens if we turn off the lights.. It stops instantly... Why sir?
>>>It stops instantly>> NO all have a decay time. Incandescent lamps much longer than fluorescent lamps and use LDEs - The color of the light and the intensity of an incandescent light depends exclusively on on the temperature of the filament. When you turn the light off, the flamnets cool. - use google.
Hello professor, I loved this lesson but I was wondering why you didn't talk about the situation of a wire running thought a magnetic field which seems to be a major part of my high school physics exercises
I have a question. The magnetic braking means that a force is slowing down the conductor right? But in a previous lecture he said that a magnetic field never can do work on a charge because the lorenz force is always perpendicular to the velocity so the speed can not be increased or decreased it can only change direction. But here we obviously have a change in speed when we talk about magnetic braking? So what am I missing?
Sir, we know that due to the hall effect, the lorentz force is neutralised by the electric field within a conductor. Thus a charge travelling will feel 0 N net force.My question is if a charge don't feel any force.Then why the conducting rod will feel the magnetic lorentz force?
You speak about conservation of energy. What do you think about red-shifting light due to what seems like the Universe stretching? With our current models, it seems that their energy is lost (but then again, there's the "dark" stuff and possibly other things we can't explain yet so this part may be incomplete)
Sir light is a electromagnetic wave. Sir it means that suppose there is a light in a space. It means at every point in that space there will be the oscillation of the magnetic Field. Sir now suppose I put an closed loop of wire in that space. Because there is oscillation of magnetic field at every point in that space it means there will be the change in the magnetic flux linked with the loop. Than why the current is induced in the loop which is placed in the light
sir your lectures are the very beautiful way of learning the laws of nature. sir, I have a question that can we relate or is there any relation between faraday law with the Lorentz force?
I came to this video long after it is posted, so I am wondering if Prof. Lewin is still available. I am trying to access the assignment, but the link didnt work out, can somebody help me? thank you in advance!
At minute 38:00, the Lorentz force from the current in the side that Mr. Lewin pointed to, goes in the left direction and opposes the motion as he said. But what if we look at the current from the other side of the eddy loop? The force would be in the right direction, so why is there a magnetic breaking? Shouldn't forces cancel?
Sir as we know that electric field inside a conducting wire will be zero until current will be flow through the conductor. Sir suppose there is wire. I am moving this wire such that the motion of wire is perpendicular to the magnetic field. Sir we find by Lorentz force that polarisation of the wire takes place. At one end positive charge will be induce and at one end -ve charge will be induce. There will be electric field inside the conducting wire. Sir it means there will be electric field inside the conductor but we know that electric field is zero in static situation.
There will be an E-field inside the conductor -- as long as the conductor is moving electrons will *remain pushed* to one side, no current is flowing. The q*VXB force on the electrons will be balanced by qE. Thus *E inside the conductor is VXB.* All this is covered thoroughly in web.mit.edu/viz/EM/visualizations/coursenotes/modules/guide10.pdf. PLEASE do not ask questions whose answers are already in websites that I sent you.
Lectures by Walter Lewin. They will make you ♥ Physics. Sir my question is that there can be electric field inside the conductor even when the current is not flowing.
Lectures by Walter Lewin. They will make you ♥ Physics. But in lecture 5 you say that there can be electric field inside the conductor until current is not flowing.
>>>> in lecture 5 you say that there can be electric field inside the conductor until current is not flowing.>>>> *I did not say that. READ what you wrote!!!* all your answers are here web.mit.edu/viz/EM/visualizations/coursenotes/modules/guide10.pdf To create an E-field by moving a conductor through a B field is a very special case.
38:58 46:19 Great demonstration on Eddy currents, I enjoyed it. But it brought a nagging question to mind. At this time signature, a current is passing an air gap. I was under the impression that current could only flow through air at or above the breakdown voltage of 3 MV via corona discharge. How is it that electrons pass this air gap?
I was wondering the same, what about the ring with an air gap? Does the current pass over the air? Does the resistance of the air produce heat? min 48:00
Mauricio Barda in the ring with the gap the current doesn't flow along the entire ring, rether it flows in tiny loops the thickness of the rings wall. Since the force generated scales with the size of the loop there is almost no braking force. (Voltages generated are small, but fairly straightforward to calculate if you know the dimensions of the ring and the field strength)
Around 32.50, while deriving an expression for motional emf, ultimately, we arrive at the conclusion that be it by Faraday's or by work considerations we arrive at the same expression for E. However, imagine a scenario where the magnetic field doesn't pervade the entire area of the loop. We start by pulling the moving arm outwards from an initial point where the moving arm isn't touched by the magnetic field. In such a case how would we explain the scenario from an energy standpoint?
If you were dealing with iron you would have a weakly magnetic pole depending on the direction of the current you'd have positive or negative. I'm not sure what you'd have using a more resistant semiconductor material. Could be you wouldn't have anything unless the velocity was high enough to overcome the resistance. I may have completely misunderstood what you were asking.
These lectures are great. But here in India we study these in high schools and for entrance exams in engineering colleges. Man lot of work here in this smsll age🥺
Dear Professor, you have not mentioned Nicola Tesla in your lectures! is not he the greatest contributor in the electric revolution and the one that was underrated by the entire scientific community because he was not American in contrast to Edison who was treated as a god???
When talking about Tesla, one can not compare him to any other scientist because that would only limit his work, life and being on one subject. When we really sum it up, Tesla was the greatest of people known to us. I know there are lots of greater people with far advanced knowledge, but as you know they are not quiet famous among our 'western civilisation'. My humble opinion. Also my opinion- Sir Lewin, you are very good teacher :)) Thank you.
sir , at 38.00 you said that the lorentz force opposes the motion as the current comes out of the blackcoard but there must be lorentz force on the other side too.... right where the current goes into the blackboard but here the lorentz force will aid the motion...seems confusing that the net force would be zero acting on the plate . please explain me this ....
Sir I doubt will humans ever be able to fly given the conditions are favourable being Human a good conductor ,and increased magnetic field power balancing the gravitational pull ? And also how can we manage the heat produced by eddy currents ? Can the atmosphere above will do conduction to dissipate fair enough to live while levitated up above in the sky ?
Hello Professor Lewin or anyone who can answer this question for me. In the demonstration with the copper pendulum, was it the opposing Lorentz force that slowed the pendulum down on the KE being converted to heat, or a combination of both?
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. Homework and exams are posted below the video thumbnails. *I guarantee you that you will then not fail the Physics portion of any exam*
Professor I have something to ask, imagine if there are two cross bars on the that conducting loop.Those two are identical.They move with the same velocity in the same direction.Then the amp meter reads the same current as when there was only one cross bar.Why is that .
Dear Mr. Walter, I have an electromagnet coil for holding/lifting.. it has iron core and surrounded also by iron (not homemade). I want to use it with NEO magnets to generate electricity (because it has the iron so is better than a naked homemade coil), My question is: Why when I tried to give this coil electricity (to test it as an electromagnet) and placed a normal magnet in front of the coil, why the magnet is attracted in both directions? shouldn't the iron core act as a magnet with two poles when I apply a voltage? then the coil should repel the magnet in one of the sides? Thank you in advance! :)
+Lectures by Walter Lewin. They will make you ♥ Physics. Thank you for your reply. Perhaps I didn't explain my question well, I'm not going to use only magnets, I just wanted to test the coil that I'm using as a magnet. So let's forget for now about the generator.. Why when I apply a DC voltage on the coil (and it becomes a magnet) why it attracted the NEO magnets in both sides and not only one? this is the coil I'm talking about: image.dhgate.com/albu_259524997_00/1.0x0.jpg Thank you! :)
+Rajaa Kahel Try to figure out the B-field geometry of the NEO magnets. I had several and I recall that I was surprised that the fields were not what I expected. Once you are sure that you know the field geometry I suggest you contact me again.
+Lectures by Walter Lewin. They will make you ♥ Physics. Thank you very much for your time! I feel shy to ask more questions.. So I will just try to figure out my self by experimenting...
+Rajaa Kahel Do not feel shy. If the S and N poles are NOT each on a flat side of the NEO magnets then you have an explanation. I recall that I had NEOs for which that was the case. If the S and N poles are on the flat sides . . . . Imagine you use a weak magnet - your electromagnet will attract both sides as its is B-field is much stronger than that of the weak magnet. I would then have to conclude that your Electromagnet creates a much stronger field than your NEO magnets. However, you can only conclude that if you are sure that the N and S poles are on the flat parts of the NEO magnets.
my question is with magnetic damping...the kninetic energy of the moving object is reduced due to the force from the eddy currents and the applied magnetic field. This energy is dissipated in the form of I^2R losses..correct? But what if the object is superconducting, shouldn't there still be an opposing force due to eddy currents and the kinetic energy of the object reduced? where did the energy go if there can be no I^R losses in a superconductor???
Super conductors will repel any magnetic field. en.wikipedia.org/wiki/Meissner_effect. Thus there will be no energy dissipation in the super conductor. However, electric currents can flow inside super conductors. That's how the LHC powers it's magnets!
Sir suppose there is a magnet. The magnet is oscillating. Hence the magnetic field at any point in the space will be changing. Sir sir is changing magnetic field at a point in space will produce electric field at that point. Sir it means that when we move the magnet in a particular space than electric field also produced at that space. Sir please please explain
Thanks prof for these great lectures , but I confused at one point ,which is difference between eddy current and induced current as both are produced by change in magnetic flux as one gives emf and other produces heat
On multiple occasions starting around 32:00 in the video, in the English captions, it's spelled "Lawrence" force, when I think it should be "Lorentz" force.
Ok, thank you for the reply! At first, I was a bit confused by this new "Lawrence?" force, but its not too hard to figure out what its supposed to be ;)
Sir I love physics.I would also like to start a youtube channel( I'm from INDIA and I wish to deliver the class in my native language Tamil) and deliver my lectures by understanding concepts from u ..But I feel more shy.😐😞.. Don't know what to do sir.. Please guide me if possible..🙏
At 33:30 you say when we change the velocity in opposite direction the current flows in square wire in opposite direction won't that flow of current now contribute to the existing magnetic field causing Lenz law now obsolete ??? I know this not the case just need a clarification on how the change of current affects the already existing b field
@@matheworman6308 there is no paradox - of course, you are entitled to believe what you want to believe. But you have a more interesting option and that is to become educated
Sir suppose there is a conducting wire. Sir the conducting wire moves in a magnetic field such that the motion of the wire is perpendicular to the steady magnetic field. Sir there will be the Lorentz force on the charge in the wire. So there will be induced +ve charges at on end of the wire and -ve at other end. The induction of charge in wire is due to Lorentz force F=q(v*B).Sir now suppose that the conductor is not moving. Sir but now there is change the magnetic field. Sir how in this case there will be +ve charge induced at one end and -ve charge at other end. how there will be Lorentz force on charge in the wire. Sir sir when the conductor is not moving v is zero.
A changing magnetic field but no motion of the wire and no motion of the B-field) will not create a potential difference between the ends of the wire. But changing B-fields can cause Eddy currents in the wire depending on the geometry (direction and thickness of the wire).
Sir I am in 10th standard. I have a doubt in one question. I hope you will help me. Q student boys water in an electric kettle for 20 minutes .Using the same main supply he wants to reduce the boiling time of water. To do so should he increase or decrease the length of the heating element?
Dear Professor, can we calculate the magnetic field the induced current generates using Amperes law? I guess if rate of change is slow, we can even neglect the Amperes law correction, just use Curl H = J where J=sigma E, where E is the EMF given by solving Curl E = -dB/dt? I always confuse myself on this concept.
Just a general question that I always wondered. Can we go through this flow chart? Curl E = -dB/dt. From here we get induced current I (or current denisty J = sigma *E). From this we get from Amperes Law Curl H = J.
Ampere's Law is NOT connected to Faraday's Law. They are independent eqs. You cannot derive Amp ;aw from Faraday's Law. But you can calculate the current that is due to Faraday in a given circuit and that allows you then to calculate the B field produced by that current. The dB/dt of that B-field, in general is VERY low. If you have no inductor in your circuit. Only R's and C's, and you use AC power. The dB/dt through an OPEN surface attached to a closed loop caused by the variable B field depends ONLY on the inductor value of your circuit and that is near zero of there is no L in the circuit.
At 38:10 you told that the lorentz force pushes the metal out of the field. But when i applied Left hand rule, the force turned out to be towards the right side. Why is that so ?
Sir suppose there is a straight wire. This wire is thrown from the height to the earth surface. Sir as we know that emf will be produced in the straight wire. Sir Mr Faraday says that emf will induced in a loop only when magnetic flux will be changed linked with the surface . Sir how now emf is induced between the end the wire. Its means magnetic flux is changing. sir how magnetic flux is changing with the falling straight ire
May I please ask a question: if the magnet enters the aluminum block at different speeds, will the generated magnetic braking force be different as well? Say more braking force at higher speed?
Professor I am studying physics again. I studied it in high school and graduation and didn't really understand anything. I have been constantly watching your videos and it has indeed changed the way I used to perceive Physics. Now it is so beautiful that if I am not well, i watch these lectures or study Physics. Huge respect for you. I wish I could meet you someday.
Nobody meets the professor until they solve the Boolean Pythagorean Triples problem.
@@NuVids2025What the hell is that?
This website contains all my 94 course lectures (8.01, 8.02 and 8.03) with improved resolution. They also include all my homework problem sets, my exams and the solutions. Also included are lecture notes and 143 short videos in which I discuss basic problems.
ENJOY!
Lectures by Walter Lewin. They will make you ♥ Physics. Sir you say that a changing magnetic flux linked with the coil produce current in the coil. Sir classical physics says that it is due to the inertia of the coil. The coil does not want to change the magnetic flux linked with it. That's why it produced current to oppose the changing magnetic flux. Sir how the reason given by the classical physics is not correct.
Faraday's Law is classical Physics and *it is 100% correct!!!!* It runs our entire economy. There can not be any confusion. If this is not enough for you, consult google.
@@physl2787 this kind of inertia is also called as the self or mutual inductance of coil, which can be verified by both Faraday's or Lenz's law..
Sir can u mathematically explain WHY EARTH BEHAVES LIKE BAR MAGNET?
BIG FAN SIR.
@@shivaramanshukla5013 en.wikipedia.org/wiki/Earth%27s_magnetic_field
cosmosmagazine.com/geoscience/what-creates-earth-s-magnetic-field
I'm so glad I found your videos Professor. I'm always trying to find things to learn more about these kinds of subjects and your lectures are better than anything that I've been able to find. Thank you so much!
My pleasure
Thanks to this lecture (part about eddy currents and mag braking) I finally understand why a magnet falls so slowly when we let it fall through a hollow conducting cylinder :)
All of your lectures are fascinating and dense with information. I especially enjoy 8.02, but would recommend all of your lectures as required learning for anyone interested in physics!
I actually got to learn the importance of eddy current as It has many technological uses ,thanks pro
The lecture was remarkable, even today Micheal Faraday is not alive, but by watching this lecture and all experiments that you have done, I found Micheal Faraday is still there.. especially experiments helped me a lot.. thank you.
:)
Sir, In eddy current experiment, what kind of material (conductor) you have used? Magnetic or non- magnetic conductor..?
The material I used was NOT a permanent magnet.
Thank you, professor! I get so much knowledge from these lectures and I appreciate it a lot!
I can not appreciate your lectures enough. I'm doing my Master's in Germany and working on Magnetic field influence on Electrochemical process. I was interested in your take on the Magnetic field effect on a charge carrier of an ion conductor (or electrolytes). Thank you! God Bless you, Sir.
That's great!
@@lecturesbywalterlewin.they9259 Thank you, Sir ;)
Interesting to note that the shaft in the Indian Point power station that I visited that drives the dynamo is .8m in diameter and about 60m long and made of solid steel. The torque on the shaft causes the shaft to twist 270 degrees our of true when generating electricity! Real work is happening! Thanks for the lectures
dear professor you are the best person I have ever heard,i can understand more from 10min than any one I ever heard not MIT must have lost there mind, you're an inspiration you are my hero you give me inspiration and give me great ideals in anti gravity,people call me a nut job but I have some success in small experiments (it's not really gravity that we are defeating) the earth is a big magnet 😁
thanks, Michael, for your kind words.
I am 60 now. And addicted to Walter's lectures and binge watching all his videos. I loved the Dynamo demo in this video. In my younger days I used to see small Dynamo that can be attached to the backwheel of the Bicycle. A light bulb in the front connected to the dynamo serves as light source during night time riding in the dark. When dynamo rotator attaches to the wheel it's a bit more difficult to pedal the Bicycle wheel (Lenz's law).
I was supposed to have nice timw with Netflix but ended up here with full lecture.........i love it ,couldn't able to leave....
Yes his lectures are addictive. Great teacher.
Hello professor Walter. Im a Physics entusiast, i dont have any grade or college education. Im just making this coment to thank you. You thought me everything i know about Physics!
"You can't even do it man!" :) That was so funny hahahah! I loved it :)
you are a great man, i'm doing research on an application that uses ZVS and i found you ! good job!
When the power grid becomes overloaded, generators slow down slightly (frequency drops from 60Hz) and motors slow down and do less work over time. Generation and load are balanced by AC line frequency. Underfrequency relays automatically drop load at about 59.5Hz to prevent generator damage and customer damage. When you turn on a light bulb in Boston, the frequency drops a very small amount on the entire east coast until generation speeds up a very small amount to return toward 60Hz. Time keeping is corrected after midnight when load drops and there is excess generation available. The amount of power a generator adds to the power grid is controlled by it's generating turbine speed (frequency) and not by voltage as most people expect.
I really doubt that Walter Lewin camping flashlight (27:46) generates 120 Watts. More likely 1 Watt. or less. Most people can generate about 60 Watts with a real struggle on a bicycle.
Thanks Walter, I do love physics and your lectures.
>>>I really doubt that Walter Lewin camping flashlight (27:46) generates 120 Watts. >>>
*what made you think so??? I never said that.* Watch the video again. My dynamo would probably produce 5-10 W if I work very hard!.
(27:46) "This is a 120 Watt light bulb and I keep it going all the time". Either way, you have a great way of personally connecting with your students and that was one example. Thank you.
ha ha ha ha ha ha ha didn't you realize that that was a joke! Wasn't that obvious!
I thought the joke was you being in the Boston mountains and doing a lot of mountaineering (27:25).
Thank you Prof. Lewin for your fabulous lectures! In your demonstration with the copper pendulum being slowed by the solenoids, you used power conservation arguments to explain the dampening. I am having trouble picturing how the dampening force (the direction especially) is created using F=qvXB and Faraday's law. Could you please comment? Thank you in advance.
+Wallace Yang Eddy currents are not easy to model. Yet, it is clear that they consume energy (ohmic heat). Where does that energy come from? It has to be gravitational potential energy since that's the only energy source available. If you moved a metal plate through a magnetic field you will have to do work. You will have to push! Your work emerges as heat in the metal produced by eddy currents. There is a q(vXB) force on your metal that you have to overcome. You move the metal with velocity v. The free electrons in the conductor start moving.
Belated happy teacher's day sir!!
Sorry its too late!!
(In India we celebrate it on 5th Sept.)
Thank you very much sir for making us love physics as you do!!!😊😊🙏😀
If only i had a lecturer with this high quality, i would be a physicist.. unfortunately i only got formulas in learning physics just to calculate without knowing the concepts... and it makes physics is a mystery and boring.. thank you very much Prof, u rock!
Very captivating. Thank you for these.
Helped me pass electrodynamics. Great lectures
Awesome lecture on magnetic braking. I'm pretty sure metals like aluminum that respond with such vigor to electromagnets do so, because they produce a greater number of eddies than copper, and it possible an alloy out there somewhere would be even more responsive. I was working on a problem in my head using magnetic braking, and thinking I can't have it correct. All that kinetic energy coming to a halt, but where's the equalization. Then you said it generates heat, and the balance of the universe was once again as it should be. I get focused on something and over look a basic function of objects doing work.
Dear Sir, if any student any where in the world doesn't understand your 8.01, 8.02 and 8.03 not grade pass/fail but alteast general ideas/concepts, they are not eligible to pursue their engineering .. that should be made global law.. as without these basics no research could be done.. by those graduating students..
take a bow Sir from india..
and in any univestity engineering disciple.. this should be order of course structre.
1) math series all from calculus to differential equeations ..
2) your phyiscs/nature series..
........
rest all doesnt matter and student can fully appreciate and understand any discipline..
Thank you sir... your lectures is helping me in Neet preparation
I strongly suspect my teachers themselves didn’t understand what they were teaching. Just regurgitating what’s in text books is not teaching and that’s what they did. Everything was geared towards doing well in exams and not stimulating student interest. This is a completely different approach!
Wish I would have been in that class and enjoyed the live show!
:)
Prof. You rotate the loop in x axis which the magnetic flux would not change. You should have rotated in y Axis in order angle teta and also flux to change.
WL: *breaks a lightbulb*
Also WL: "Now that, runs our economy!"
Hi! Thanks for the videos. I had a question: in the last example, the one of the loop that has a hole, how can the current jump over the gap?? Why is there current going through the gap?
Thank you!!
how many minutes into the video?
@@lecturesbywalterlewin.they9259 46:31
Thanks!
Wait a second ! When you lit the light bulb by swiftly moving the coil between the magnetic field, didn't you feel a magnetic braking ?
Great thanks sir I want to participate in Ipho this year or next and Ur lectures are really helpful
But I have a question:
When U talked about the motional EMF u just took the case of a rod what will be the situation if had a conducting sphere or any other shape
I hope u answer and thanks!
great sir you made me love physics
Sir, at 5:20 how will you be able to rotate that loop with a constant angular velocity? If you were applying a constant torque , the induced current will develope an opposing torque which is also sinusoidal and therefore the resultant torque applied to the loop is not zero then , how the angular velocity will be constant ?
Good afternoon sir, you lectures have helped me a lot on understanding the subject, l am experiments with making a generator , but could not produce electricity, l suppose l should keep rotating a lot more. , Which l will try again
Keep it up
After the professor the cameraman is the one who pursue the most knowledge in physics 😁😁
Respect to Sir Walter from Pakistan🙇♂
thank you
When you were finding direction of Lorentz force on the conductor in case of Magnetic breaking, there were 2 possible directions of Lorentz force......if we consider the solid disc perpendicular to the page then once current will come out of page and once current will go into page but you found Lorentz force for one direction only....(38:02)????
Lorentz force will reverse when dphi/dt changes from + to minus. In both cases heat is produced inside the disc. Thus the disc will slow down as it enters the B-field and also as it leaves the B-field. That's called magnetic breaking.
When discussing the eddy currents, you say the current must pass through the air, but why doesn't the induced current just travel on the surface of the conductor (at 39:24)? Any help would be greatly appreciated!
Since childhood, I have been worried about the question, how can they not understand the obvious truth, which is that the area of the contour has nothing to do with the emergence of EMF? There is no way to create a time-varying magnetic field so that the magnetic induction vector simply "sticks" into the circuit, as is always shown in lectures. The magnetic lines of force ALWAYS enter the circuit through its borders from the outside. And, thus, there is a PROCESS of crossing the conductor of the contour by the magnetic lines of force. Consideration of this process by means of the contour area is a mathematical abstraction that has nothing to do with the physics of the process. Of course, everything converges numerically, because the area of the contour is directly related to the perimeter of this contour, but PHYSICALLY the process occurs in a completely different way. To understand WHY Maxwell wrote it down in this form, you should read Maxwell's treatise on electricity and magnetism and pay attention to the MODEL from which his equations are derived.
You can do a very simple experiment. For the case when the area of the circuit changes, the current will be proportional to the number of moving conductors. That is, if you put 2, 3 or 5 conductors at a short distance on the open edge of the circuit and move them all together to the right or left, the current will be approximately 2, 3 or 5 times more than with one conductor. Since the moving conductors will influence each other as well, the ratio is inaccurate. Of course, the magnetic field must be sufficiently uniform along the trajectory. Also, if you move the entire circuit in a uniform magnetic field, but create unequal conditions for the front and rear conductors (cover one of them with one or another metal, choose different materials, etc.), EMF and current will also arise. Moreover, it follows from Faraday's law that no PROCESSES take place in an open loop! BUT! Try to get close to the output terminals of the idle step-up transformer! You will be shocked even BEFORE you touch the terminals! HOW did the transformer know that you approached ?!
I am trying to visualize the geometry of the open surface with a closed loop in Faraday's law, and what I have done is using a helicoid frame (shorturl.at/cxSW3) to match the relationship between the open surface and its associated closed loop. However, I still can not make it. For example, In this helicoid mentioned above, the surfaces which extend from different portions of the frame seem to intersect. Does that matter? Or I went to wrong direction to approach this problem? Any help is appreciated, thanks a lot.
Thank u so much Feynman
My name is Feywin
@@lecturesbywalterlewin.they9259 sir you are teaching us as like as Feynman did ....😍
@@mamduarahman2665 he is teaching us as lewin did
Sir you said that in ac circuit(making a bulb glow) bulb still glows(as heating effect of tungsten still remains) even when current is 0
Sir but what happens if we turn off the lights..
It stops instantly...
Why sir?
>>>It stops instantly>>
*NO all have a decay time.* Incandescent lamps much longer than fluorescent lamps and use LDEs - use google.
😊😅Thank You sir!!
>>>It stops instantly>>
NO all have a decay time. Incandescent lamps much longer than fluorescent lamps and use LDEs - The color of the light and the intensity of an incandescent light depends exclusively on on the temperature of the filament. When you turn the light off, the flamnets cool. - use google.
Lectures by Walter Lewin. They will make you ♥ Physics. Ok sir! 😊😅
Hello professor, I loved this lesson but I was wondering why you didn't talk about the situation of a wire running thought a magnetic field which seems to be a major part of my high school physics exercises
He told..bro...motional emf
At ground 5:30 was confused between angular frequency and angular velocity. But I think both are just fine
tehy ar same.
Thank you so much professor lewin
Perfect explanation
I have a question. The magnetic braking means that a force is slowing down the conductor right? But in a previous lecture he said that a magnetic field never can do work on a charge because the lorenz force is always perpendicular to the velocity so the speed can not be increased or decreased it can only change direction. But here we obviously have a change in speed when we talk about magnetic braking? So what am I missing?
Sir, we know that due to the hall effect, the lorentz force is neutralised by the electric field within a conductor. Thus a charge travelling will feel 0 N net force.My question is if a charge don't feel any force.Then why the conducting rod will feel the magnetic lorentz force?
>>>Thus a charge travelling will feel 0 N>>> *not true*
watch ruclips.net/video/PJqOaHBgr30/видео.html
But the hall effect tells that
Dynamos don't produce AC. Dynamos produce DC. Alternators produce AC.
Very interesting Prof.
You speak about conservation of energy. What do you think about red-shifting light due to what seems like the Universe stretching?
With our current models, it seems that their energy is lost (but then again, there's the "dark" stuff and possibly other things we can't explain yet so this part may be incomplete)
+lauroflorin Energy is conserved. cds.cern.ch/record/777175/files/0407077.pdf
@@lecturesbywalterlewin.they9259
Very thank you for that link. It saves my life or at least helps me arguing pro energy conservation.
Hey guess what he replies as well. Thank you. If i ever watched videos about EMT is only because of you.
:)
Sir light is a electromagnetic wave. Sir it means that suppose there is a light in a space. It means at every point in that space there will be the oscillation of the magnetic Field. Sir now suppose I put an closed loop of wire in that space. Because there is oscillation of magnetic field at every point in that space it means there will be the change in the magnetic flux linked with the loop. Than why the current is induced in the loop which is placed in the light
SIR SORRY I FORGET HERE TO WRITE ''NOT''. HENCE my question is that why the current is NOT induced in the loop which is placed in the light.
Great lectures!
sir your lectures are the very beautiful way of learning the laws of nature. sir, I have a question that can we relate or is there any relation between faraday law with the Lorentz force?
:)
I came to this video long after it is posted, so I am wondering if Prof. Lewin is still available. I am trying to access the assignment, but the link didnt work out, can somebody help me? thank you in advance!
At minute 38:00, the Lorentz force from the current in the side that Mr. Lewin pointed to, goes in the left direction and opposes the motion as he said. But what if we look at the current from the other side of the eddy loop? The force would be in the right direction, so why is there a magnetic breaking? Shouldn't forces cancel?
no
Have we worked enough with graphene and copper or iron composites (grains along with graphene oxide) to make a dent in better conductors/magnets?
Sir as we know that electric field inside a conducting wire will be zero until current will be flow through the conductor. Sir suppose there is wire. I am moving this wire such that the motion of wire is perpendicular to the magnetic field. Sir we find by Lorentz force that polarisation of the wire takes place. At one end positive charge will be induce and at one end -ve charge will be induce. There will be electric field inside the conducting wire. Sir it means there will be electric field inside the conductor but we know that electric field is zero in static situation.
There will be an E-field inside the conductor -- as long as the conductor is moving electrons will *remain pushed* to one side, no current is flowing. The q*VXB force on the electrons will be balanced by qE. Thus *E inside the conductor is VXB.* All this is covered thoroughly in web.mit.edu/viz/EM/visualizations/coursenotes/modules/guide10.pdf. PLEASE do not ask questions whose answers are already in websites that I sent you.
Lectures by Walter Lewin. They will make you ♥ Physics. Sir my question is that there can be electric field inside the conductor even when the current is not flowing.
yes - it's all here
web.mit.edu/viz/EM/visualizations/coursenotes/modules/guide10.pdf
Lectures by Walter Lewin. They will make you ♥ Physics. But in lecture 5 you say that there can be electric field inside the conductor until current is not flowing.
>>>> in lecture 5 you say that there can be electric field inside the conductor until current is not flowing.>>>>
*I did not say that. READ what you wrote!!!*
all your answers are here web.mit.edu/viz/EM/visualizations/coursenotes/modules/guide10.pdf
To create an E-field by moving a conductor through a B field is a very special case.
38:58
46:19
Great demonstration on Eddy currents, I enjoyed it. But it brought a nagging question to mind.
At this time signature, a current is passing an air gap. I was under the impression that current could only flow through air at or above the breakdown voltage of 3 MV via corona discharge. How is it that electrons pass this air gap?
+Webb Telescope Dry air has a high resistivity but it is not zero. Humid air can have a low resistivity..
Current isn't passing through the air gap. Each tooth breaks up the maximum size of the current loop so the total braking is much less.
That is correct!
I was wondering the same, what about the ring with an air gap? Does the current pass over the air? Does the resistance of the air produce heat? min 48:00
Mauricio Barda in the ring with the gap the current doesn't flow along the entire ring, rether it flows in tiny loops the thickness of the rings wall. Since the force generated scales with the size of the loop there is almost no braking force. (Voltages generated are small, but fairly straightforward to calculate if you know the dimensions of the ring and the field strength)
This is for which exam
Around 32.50, while deriving an expression for motional emf, ultimately, we arrive at the conclusion that be it by Faraday's or by work considerations we arrive at the same expression for E. However, imagine a scenario where the magnetic field doesn't pervade the entire area of the loop. We start by pulling the moving arm outwards from an initial point where the moving arm isn't touched by the magnetic field. In such a case how would we explain the scenario from an energy standpoint?
If you were dealing with iron you would have a weakly magnetic pole depending on the direction of the current you'd have positive or negative. I'm not sure what you'd have using a more resistant semiconductor material. Could be you wouldn't have anything unless the velocity was high enough to overcome the resistance.
I may have completely misunderstood what you were asking.
These lectures are great. But here in India we study these in high schools and for entrance exams in engineering colleges.
Man lot of work here in this smsll age🥺
Dear Professor, you have not mentioned Nicola Tesla in your lectures! is not he the greatest contributor in the electric revolution and the one that was underrated by the entire scientific community because he was not American in contrast to Edison who was treated as a god???
Did I single out Edison? I agree Tesla was an equal giant.
Neither of them can be compared with the godfathers of E&M (Faraday, Ampere, Maxwell).
When talking about Tesla, one can not compare him to any other scientist because that would only limit his work, life and being on one subject. When we really sum it up, Tesla was the greatest of people known to us. I know there are lots of greater people with far advanced knowledge, but as you know they are not quiet famous among our 'western civilisation'. My humble opinion. Also my opinion- Sir Lewin, you are very good teacher :)) Thank you.
sir , at 38.00 you said that the lorentz force opposes the motion as the current comes out of the blackcoard but there must be lorentz force on the other side too.... right where the current goes into the blackboard but here the lorentz force will aid the motion...seems confusing that the net force would be zero acting on the plate .
please explain me this ....
Sir I doubt will humans ever be able to fly given the conditions are favourable being Human a good conductor ,and increased magnetic field power balancing the gravitational pull ?
And also how can we manage the heat produced by eddy currents ?
Can the atmosphere above will do conduction to dissipate fair enough to live while levitated up above in the sky ?
Hello Professor Lewin or anyone who can answer this question for me. In the demonstration with the copper pendulum, was it the opposing Lorentz force that slowed the pendulum down on the KE being converted to heat, or a combination of both?
What the relation between open surface and close loop? I couldn't understand properly the concept.
Faraday's Law
Sir, I’m in 10th grade now in India and preparing for jee advanced , how your lectures are helpful for me and how can I make use of them
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. Homework and exams are posted below the video thumbnails. *I guarantee you that you will then not fail the Physics portion of any exam*
Actually jee adcance 2020 question came from your eddy currents demonstration.
Do you explain in any other lectures why iron cores in motors, transformers, and generators are laminated?
ask google
energy conservation - suppression of Eddy currents
Professor I have something to ask, imagine if there are two cross bars on the that conducting loop.Those two are identical.They move with the same velocity in the same direction.Then the amp meter reads the same current as when there was only one cross bar.Why is that .
question unclear - be more precise
Thank you Dr. Lewin. raphael santore
Electricity without cables....
Thank you for this video
Almost all electricity that we use come from rotatting loop it's wiref
Thanks professor
Sir u explained very well .
☺
Excellent lecture Sir 🙏🙏🙏🙏
Keep watching
Hi. What will happen if we use an electric conductor that is also a magnetic substance during the damping?? how will it work in this case?
Dear Mr. Walter, I have an electromagnet coil for holding/lifting.. it has iron core and surrounded also by iron (not homemade). I want to use it with NEO magnets to generate electricity (because it has the iron so is better than a naked homemade coil), My question is: Why when I tried to give this coil electricity (to test it as an electromagnet) and placed a normal magnet in front of the coil, why the magnet is attracted in both directions? shouldn't the iron core act as a magnet with two poles when I apply a voltage? then the coil should repel the magnet in one of the sides? Thank you in advance! :)
+Rajaa Kahel You cannot generate electricity with magnets only.
I will be able to give you an answer if you send me a picture of your setup.
+Lectures by Walter Lewin. They will make you ♥ Physics. Thank you for your reply. Perhaps I didn't explain my question well, I'm not going to use only magnets, I just wanted to test the coil that I'm using as a magnet. So let's forget for now about the generator.. Why when I apply a DC voltage on the coil (and it becomes a magnet) why it attracted the NEO magnets in both sides and not only one? this is the coil I'm talking about:
image.dhgate.com/albu_259524997_00/1.0x0.jpg
Thank you! :)
+Rajaa Kahel Try to figure out the B-field geometry of the NEO magnets.
I had several and I recall that I was surprised that the fields were not what I expected. Once you are sure that you know the field geometry I suggest you contact me again.
+Lectures by Walter Lewin. They will make you ♥ Physics. Thank you very much for your time! I feel shy to ask more questions.. So I will just try to figure out my self by experimenting...
+Rajaa Kahel Do not feel shy. If the S and N poles are NOT each on a flat side of the NEO magnets then you have an explanation. I recall that I had NEOs for which that was the case.
If the S and N poles are on the flat sides . . . . Imagine you use a weak magnet - your electromagnet will attract both sides as its is B-field is much stronger than that of the weak magnet. I would then have to conclude that your Electromagnet creates a much stronger field than your NEO magnets. However, you can only conclude that if you are sure that the N and S poles are on the flat parts of the NEO magnets.
Fantastic lecture :)
Glad you think so!
my question is with magnetic damping...the kninetic energy of the moving object is reduced due to the force from the eddy currents and the applied magnetic field. This energy is dissipated in the form of I^2R losses..correct? But what if the object is
superconducting, shouldn't there still be an opposing force due to eddy currents and the
kinetic energy of the object reduced? where did the energy go if there can be no
I^R losses in a superconductor???
Super conductors will repel any magnetic field. en.wikipedia.org/wiki/Meissner_effect. Thus there will be no energy dissipation in the super conductor. However, electric currents can flow inside super conductors. That's how the LHC powers it's magnets!
Can you please explain why will the disk slow down when the Eddy Currents are induced?
I cannot add to the clarity of my lecture. If you did not understand my explanation, please use google
how does the flying aeroplane develop potential between two wings?? luv ur lecture. .
use google
Amazing that you can measure the current due to the magmetic field of the Earth
Dear Professor, what if the conductor is moving in the magnetic field?
watch this lecture
Sir suppose there is a magnet. The magnet is oscillating. Hence the magnetic field at any point in the space will be changing. Sir sir is changing magnetic field at a point in space will produce electric field at that point. Sir it means that when we move the magnet in a particular space than electric field also produced at that space. Sir please please explain
Yes, a moving magnetic field produces an electric field.
Curl(E)=-dB/dt
Thanks prof for these great lectures , but I confused at one point ,which is difference between eddy current and induced current as both are produced by change in magnetic flux as one gives emf and other produces heat
Eddy currents are produced by magnet flux changes (thus Faraday's Law).
Induced fields are produced by external E-fields.
Eddy currents are produced by magnet flux changes (thus Faraday's Law). Induced E-fields are produced by external E-fields., not by Faraday's Law.
ok thanks prof .
On multiple occasions starting around 32:00 in the video, in the English captions, it's spelled "Lawrence" force, when I think it should be "Lorentz" force.
I know - I cannot change it - it's does not worry me too much
Ok, thank you for the reply! At first, I was a bit confused by this new "Lawrence?" force, but its not too hard to figure out what its supposed to be ;)
Parts of cc are phonetic as the people who wrote it are not Physics majors.
Ah, I see! Thank you once again, professor.
Sir I love physics.I would also like to start a youtube channel( I'm from INDIA and I wish to deliver the class in my native language Tamil) and deliver my lectures by understanding concepts from u ..But I feel more shy.😐😞.. Don't know what to do sir.. Please guide me if possible..🙏
I can't help you. Ask Physics Wallah - Alakh Pandey
@@lecturesbywalterlewin.they9259 Thank U legend..Stay safe🙂
Sir if we use two turns very closely, will the emf be twice
a coil with N turns will have an N times larger EMF than a coil (with same radius) with one turn.
At 33:30 you say when we change the velocity in opposite direction the current flows in square wire in opposite direction won't that flow of current now contribute to the existing magnetic field causing Lenz law now obsolete ??? I know this not the case just need a clarification on how the change of current affects the already existing b field
question unclear
@@matheworman6308 there is no paradox - of course, you are entitled to believe what you want to believe. But you have a more interesting option and that is to become educated
Sir suppose there is a conducting wire. Sir the conducting wire moves in a magnetic field such that the motion of the wire is perpendicular to the steady magnetic field. Sir there will be the Lorentz force on the charge in the wire. So there will be induced +ve charges at on end of the wire and -ve at other end. The induction of charge in wire is due to Lorentz force F=q(v*B).Sir now suppose that the conductor is not moving. Sir but now there is change the magnetic field. Sir how in this case there will be +ve charge induced at one end and -ve charge at other end. how there will be Lorentz force on charge in the wire. Sir sir when the conductor is not moving v is zero.
A changing magnetic field but no motion of the wire and no motion of the B-field) will not create a potential difference between the ends of the wire. But changing B-fields can cause Eddy currents in the wire depending on the geometry (direction and thickness of the wire).
Sir I am in 10th standard. I have a doubt in one question. I hope you will help me.
Q student boys water in an electric kettle for 20 minutes .Using the same main supply he wants to reduce the boiling time of water. To do so should he increase or decrease the length of the heating element?
Dear Professor, can we calculate the magnetic field the induced current generates using Amperes law? I guess if rate of change is slow, we can even neglect the Amperes law correction, just use Curl H = J where J=sigma E, where E is the EMF given by solving Curl E = -dB/dt? I always confuse myself on this concept.
how many minutes into the lecture?
Just a general question that I always wondered. Can we go through this flow chart? Curl E = -dB/dt. From here we get induced current I (or current denisty J = sigma *E). From this we get from Amperes Law Curl H = J.
Ampere's Law is NOT connected to Faraday's Law. They are independent eqs. You cannot derive Amp ;aw from Faraday's Law. But you can calculate the current that is due to Faraday in a given circuit and that allows you then to calculate the B field produced by that current. The dB/dt of that B-field, in general is VERY low. If you have no inductor in your circuit. Only R's and C's, and you use AC power. The dB/dt through an OPEN surface attached to a closed loop caused by the variable B field depends ONLY on the inductor value of your circuit and that is near zero of there is no L in the circuit.
at 19:16 60Hz? :)
At 38:10 you told that the lorentz force pushes the metal out of the field. But when i applied Left hand rule, the force turned out to be towards the right side. Why is that so ?
You must have made a mistake. The B field in which we move the disc is upwards!
yeah! Got it Prof. Thank you very much for your spontaneous replies.
Any Eddy current requires ENERGY and that energy is provided by gravity (that is the ONLY energy source). Thus the object MUST slow down in its fall.
Thank you sir.
Sir suppose there is a straight wire. This wire is thrown from the height to the earth surface. Sir as we know that emf will be produced in the straight wire. Sir Mr Faraday says that emf will induced in a loop only when magnetic flux will be changed linked with the surface . Sir how now emf is induced between the end the wire. Its means magnetic flux is changing. sir how magnetic flux is changing with the falling straight ire
web.mit.edu/viz/EM/visualizations/coursenotes/modules/guide10.pdf 10.2 motional emf
May I please ask a question: if the magnet enters the aluminum block at different speeds, will the generated magnetic braking force be different as well? Say more braking force at higher speed?
how many minutes into the lecture?
22:23 we've all been there. We've all looked at someone like that