8.02x - Lect 11 - Magnetic Fields, Lorentz Force, Torques, Electric Motors (DC)
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- Опубликовано: 12 сен 2024
- Magnetic Field, Lorentz Force, Torques, Electric Motors (DC), Oscilloscope, Historic Demo (Oersted)
Lecture Notes, Build Your Own Electric Motor - Have Fun, and Earn Extra Credit: freepdfhosting....
Assignments Lecture 9, 10 and 11: freepdfhosting....
Solutions Lecture 9, 10 and 11: freepdfhosting....
The content: Informative physics lectures and demonstrations
The thumbnail: *C H E E R I O S*
i guess im randomly asking but does any of you know a way to log back into an instagram account..?
I stupidly lost my password. I would love any assistance you can give me
@@braylenwyatt5528 reset the password
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!
Can you tell me where are these short module lectures, please ? because I can't find them
I too would like to find these.
What website are we referring to, here?
Thank you so much.
Love from Pakistan!
How can I download MIT physics book
As an engineering graduate I have seen my fair share of commutators in text books and labs, but Dr. Walter you are the only commutator likely to stay in my memory after this lecture haha :D. The buildup of the concepts leading to two very important real world applications (the current meter and the motor) was seamless and excited an intuitive approach to these. This lecture was such a good treat with my coffee ! Thank you so much for the upload, love from India !
This video was posted 5 years ago and it's still helping me passing the Electromagnetism course. Thanks professor 😝 you inspire me a lot
now 8 years ago..., even though it was filmed back in 2002, he referenced it at 21:24, he never could have imagined so many people would be watching it 2 decades later, not on such screens as he described, but on flat panel screens which make almost no noise, sip little power and aren't affected by magnets, with color accuracy unimaginable by most standards... now, oled, lcd or led so widespread... how much will change in 20 more years? But, these lectures will still be watched, so would any good lecture given in the last 60 years, physics is constant, even though this info is new to me, it was new to people 60 years ago and people discovered it 100 or 150 years ago by this point... yet, it was exactly the same for millions and billions of years
Had to watch this lecture as soon as possible to figure out what the cheerios thumbnail was all about :). I wasn't let down
Did you see it
The distortion that came from the magnet is outstanding...The best teaching ever coming from the best Professor ever that teach the subject of reality...Transparently changing our perception of the world at full potential...I wish a great health and an extreme care to you throughout this crisis time.
Thank you for sharing, sir. As a student, I admire your passion for Physics. It inspires me a lot to study about this subject!
Great
Never get enough of your lectures. I view and review,Watch and re-watch and never get tired. You nailed it prof
Ohhh!🤯 I get it:thumbNAIL!😂
Thank you Sir ... I am improving my grade with the help of uh lectures and assignments ... Simple and beautiful .. Greetings from India _ /\_
That's GREAT!
@sahithmucherla3131Yes I agree with you, thank you, Sir!🙏👏😊👍
These courses are helping me a lot in my JEE prep... Thank you professor! :)
I did my B.Sc in physics way back in 1977, but I really understood electromagnetism only after watching your videos! Amazingly what a fascinating phenomenon is this EM !
Thank you professor sir 🙏
It is fascinating that you've gone through Electricity and Magnetism and through Maxwell's equations and more, Professor, which is one the pillars of Physics, with such clear cut explanation. Thank You. Very good with all those experiments for each and very concept and equation. Truly helps concepts sink in.
exactly, the professor at my high school tries his best to show us experiments, but he can't get 200A of current just randomly or such large magnets, he also has to set it up every time... it's all really old stuff, Russian or Yugoslavian equipment from the 60s, this guy's lectures really help me conceive the topics I learn at school
Admire your teacher
Most don't even try
Plus demonstrations are not so easy. if you don't believe me check out Shankar's Yale lectures he tells you how difficult they are @@aquss33
"If you come with a magnetic monopole tomorrow, I can do this."
Hahahahahaha thank you sir you just made my day
Your Lectures are great, so enthusiastic and fun to watch.
Thank you from New Zealand!!
:))
@@lecturesbywalterlewin.they9259
Your lectures matches exactly with NCERT Physics book.
@@sandman3402 that's very true
@@lecturesbywalterlewin.they9259 Thanku from India sir
@@sandman3402NCERT? HUUUUUUH ? WHAT'S THAT? WOOPS!SORRY FOR THE CAPITALISATION!😬😬
Hello Mr Walter Lewin, first I apologize for my bad english. it's because I'm french. And you know french people speaks often bad english.
But with your famous science lectures I understand you so well !! You're the best teacher I never had, really I'm fond of your lectures. So tahnk you very very very much for your sharing of your knowledge : it seems so easy to understand with you.
This is the best lecture I’ve ever seen! Very, very, very conceptual. Brilliant Professor Walter Lewin.
thank you
Honestly Professor, I am watching this lecture for fun and as I view more and more of your lectures it becomes obvious how much rehearsal time you put in. You don't hesitate at all during the lecture and speak with conviction.
What are my lecture secrets?
A typical preparation time for 1 lecture is 60-80 hr. I do not write a script. But I dry run all my lectures 3 times before I give the lecture. 2 weeks before, 1 week before and at 6 AM of the day of the lecture. Every 5 min I have a LARGE time mark in my lecture notes (starting with 50 min, going down to zero). I have a large digital clock on the lecture desk which is set at 50 min when I start the lecture and it is counting down. Thus at ANY moment during my lecture I know within about 1 minute how much time I have left and how much time is needed to finish. Thus I NEVER overrun, I never have to do an interesting demo in haste with a sloppy explanation. I typically finish my lectures within 1 minute of 50 min. Of course during the first dry run, it ALWAYS takes near 60-70 min. I then have to do careful surgery as changes are needed. By the time it is 6 AM in the morning of the day I give the lecture I am always well synchronized between my time marks and the digital clock. My lectures have therefore become performances (like an actor on the stage).
my secrets are: *imagination, go outside the box with examples and with demos. I do often demos that will make them sit on the edge of their seats. I make the students laugh at times, make them cry, make them stop breathing, even make them wet their pants at times. I confront them as much as possible with experiences in their own lives. Where possible I include a student in a demo. I also do demos in which I take risks. I never become boring. I make them look through the equations to make the eqs come alive. I always keep their attention with my clarity, sense of humor and my LOVE for Physics. I radiate my enthusiasm - it's contagious. I can make ANYONE love physics and one of my "famous" quotes is: "if you hate physics it's only because you had a bad teacher".*
Thanks for the reply Professor! I hope I didn’t keep you up late at night writing that. I was watching the feynman lecture series you have pinned on your account and there is another one who could teach! Feynman was teaching you physics and making you understand the concepts as if you were a physicist without you knowing it. He used excellent examples and real life experiences connecting the physics to the real world much like yourself. You may not think so but you are on the same level of Feynman to *me* and I think its wonderful you continue to do this throughout your senior years. Thanks so much for the dedication and preparation time put in. It truly reflects so and you are to be admired for such amazing work 👍😃
thank you for your kind words
You’re very welcome 😊 by the way the demonstration of distorting the television image with the magnetic is awesome and I definitely have to check out some of pikes work
Sir Walter Lewin, your lectures are one of the best aid to me in studies of CBSE 12th, India. I try to grasp maximum from the contents from you. I'm grateful to such the best human. I wish I could do something for others in future.
For now, I sends you your good health wishes. May you live long and, one day I could be in your vicinity.
Oh! That day will come, I wish with optimism.
This is now in 10th grade, of course not the all of it, only flux, magnetic intensity, flemings right and left, electric motors, etc.
i can't help but envy MIT students for their courses and contests
A MOTOR CONTEST! seriously... they've got all the parts etc
i started these lectures a week ago and i can't get enough, the assignments are fun, the lectures are even more fun, i make sure to watch them at least twice to make sure i don't miss a thing..
I am so grateful for professor Walter Lewin for making his lectures available online
Greetings from Morocco... where the education system is free but sucks!
Oh wonderful challenge! I am the lab TA for the Electric Machinery course for EEs at my university and have been pushing to have the course include a project aspect that involves either building a motor or a transformer and thoroughly analyze their build as a way for students to apply their understanding of the course's material. I wish this had been done for me in either my physics or my ee courses!
Sir I have a question
Is there any footage of the MIT motor competition ? It would be really interesting to see what all the students came up with .
I would also like to thank you for these amazing lectures that are 2nd to none
They make these concepts so simple so that we can think beyond the lines rather then being regimented in our thinking like in many schools
4:38 vier :) one's native tongue never does disappear does it? Great lecture as always!
what language
From Prof.Herb Gross to Prof.Lewin,MIT have always been one of pioneers in helping students all around the World.
Thank you MIT and Prof Lewin -from Himalayas
:)
I'm a software engineer taking a career break to start a new master in photonics (16 years after graduating! :)) and I was looking for some online materials to help me refresh my knowledge on electromagnetism. Your lectures have been an enourmous help. Thanks! Bedankt!
welcome
What a magic you did it sir !!
I'm just in love with physics nowadays. Greetings from India ❤️
Thank God for this human. Thats what resonates throughout the galaxy.
Hello from Serbia.
your videos are so engrossing..i never thought i will be watching physics on internet..you are a great professor.
:)
At timestamp 20:30 where WL says..."but no one would ever say that...". Maybe, they would! Rearrange "Ns/Cm" and you have: (N/C)/(m/s), that is " Newtons/Coulomb PER meters/second, and it makes a 100% intuitive difference WRT E fields, and speed through those fields!! Unit combinations usually make all the sense in the world if you look at them differently!!
No word's to describe your way of explanation ,your the great teacher thank you for the uploading the video
It's my pleasure
fantastic lecture professor! im on the 2nd semester and has to deal with fundamental physics for another 2 months or so. you have officially brought back my love for physics!
:)
That is the best lecture I seen in my entire life about Magnets.
Your lectures are not only very interesting they are also very intertaining.
:)
Dear Professor, i hope this message reaches you.
1.)
Can you explain me 11:10 is this actually for positive charge?So for electron moving from us to the table would be from left to righ actually (magnetic)? Because i am trying to visualize whole concept, and that helps me also for other topics. So if positive charge flows from us to table then magnetic field goes from left to right, like screw. And if electron goes from us toward table than it goes from right to left?
I thought electron flowing from us to table cause right screw rule, but... en.wikipedia.org/wiki/Lorentz_force#/media/File:Lorentz_force.svg
2.)
And why some show current of the battery flows from plus to minus, when it actually flows from minus to plus, so whole schematics of electronics are wrong, even diode, it flows in other direction from minus to plus.
3.)
I also wanted to ask if flowing current through conductor causes magnetic field in some direction, is that the same reason why "flowing" conductor in magnetic field causes current?
Thanks!
13:44 *the krrk sound was perfect* 😂
Thank you for everything professor, you inspire me and are my role model
You are very welcome
Sir, I am curious about technology .... I love physics . explanation is awesome. Thank you .
😂😂 23:36 that remote though 🤣
Really make you fall in love with physics! Thank you so much! You are a living legend!
Wow, thanks!
sir, you are great.I became a big fan of you.
I never seen, even I never thought a professor like you.
There is lack of quality education in India.
Thank you! For these lectures.
thanks for your kind words
The best Indian physics teacher moved to the US (Shankar).
These lectures are awesome! Detailed, yet simplistic.
thank you
17:05 why the hell the students are looking so sleepy with this great teacher... ?
those are the students who chose the wrong course.
😂those aren't called student
50+ hours a week gets old after some time.
Answer: They’re students. Tired does not mean they aren’t enjoying it. They might just be- you won’t believe this- tired.
@@floydbenedikter9345 Indian 11th and 12th class is more stressful than these
what an awesome explanation . Great professor.
easier and more in detail compared to my highschool class (it's a special one focused on engineering). U carry me trough homeschooling. Greetings from Austria.
I love the wealth of experiments you do.
Great Sir, I salute you for your knowledge and teaching method. you are a teacher for all teachers of physics on the earth. Whoever teaches physics to students in school/college/university, He must watch your lecturer before going to teach to students.
:)
These lectures are really helpful for indian high school students for jee advanced. Very easy to understand and gives very intriguing conceptual understanding
many proff: know Physics but they dont love to share with students Your Lectures are great, so enthusiastic and fun to watch.
Thank you from PAKISTAN..
Is they are using half wave rectifier to make the motor which doesnt produce current at sometimes
Thank you, I now understand Monsoon
here current is conventional current flow correct? (opposite dir of the flow of negative electrons) in terms of the magnetic field direction right-hand rule?
edit: spoke too soon. answer was at 29:00
4:36 he said the Dutch word "vier" meaning four instead of English "four".
We love you professor :)
Dear professor at 10:18 you drew the magnetic field direction in clockwise but you said that it is outward after that but before in lecture you said if you rotate cork screw in clockwise direction than the magnetic field will point inwards ( into the blackboard) , so how here at 10:18 you showed it outwards? :)
It is according to Fleming's Left Hand Rule
I may be a wee bit underqualified, I may not be an MIT student, but sure as hell it's not going to stop me from "participating" in the motor contest. Thank You, Professor!
DON'T CUSS
Thank you professor for a great lecture!!! I have some question; can you please help me explain.
1/ So is this the way we generate electricity through wind turbine when the wind rotate the loop between the magnetic field engendering the current?
2/ Does the motor have anything dealing with AC current and DC current?
1/ YES
2/ all power stations produces AC by it's very nature. This AC can be rectified and converted into DC but that is NEVER done at power stations.
so how can we convert AC to DC?
what is AC used for and what is DC used for ?
use google
Hello dear Professor. First I want to thank you for these classes and the passion that you put for over 40 years. I'm a student and his classes are the best in the world, my teacher is boring and makes the physical look totally frightening. Thanks to you I fell in love with physics. I wanted to ask you Professor, because I want to create a kind of book with these classes, that is, write your notes and your words and compile them in a kind of book.
The idea is to study better, and practice through your readings. I wanted to know if you do not have a problem with this. I await your answer Walter.
I congratulate you, your readings are really exciting. Nahuel Nitz
go ahead! Make sure you always give me credit and always mention the source of all you print. If you sell the books, you should pay me 50% of your revenue.
Ja klar Herr Lehrer!!! Obviously I'm going to do that! You and this great work deserve it. Once again I want to thank you teacher, I am very happy for your approval. keep in touch! Dankeschönnnn
Your videos give me a huge help in understanding high school physics stuff! Thanks sir
24:32 for those who are here just figure out that "Cheerios" in the thumbnail
Sir, your style of teaching is very different nd innovative which makes physics very simple. Sir, your lectures makes environment for students, I i like your lectures
:)
Magnetic fields and electric motors are fascinating! Thank you professor!
You are welcome!
sir, first of all thank u so much to help us for making our concepts so strong. i used to think that i love physics but physics does not love me but as i started to see your videos it really helped me to retain the concepts.your way of teaching is mind blowing!
:)
sir i m preparing for medical exam and my physics is so weak .how can i solve my problem
watch all my 94 MIT course lectures. Do all the homework and take all my exams. They are all posted (pdf files) below the video thumb nails. to take the 3 courses will take you about 5 months as a full time commitment. start with 8.01.
thank u so much sir
:)
moving charge is the cause for magnetism as I relatively move fast along with the charge I would be feeling any force of magnetisation ?
I am really addicted to your lectures i am constantly watching them like a netflix series.you are brilliant sir
Keep watching
Mr. Lewin I want to ask something about the motor contest... How were you going to measure the rpm of the motors that the students made? I want to know... Did you use slow motion cameras or something else?
I used a stroboscope
Thank you sir, it was a great lecture. I was able to understand the concepts clearly.
4:36 native language never goes away 😀
wonderful piece of teaching!!!!!!
well done and long live Mr walter lewin.
I am a big fan of you prof ❤
Greetings from Indonesia..
I have a question that at 11:07 of your lecture you say that F=I×B where all of these are unit vectors,how current will be vector quantity?how can we do cross product of current?As we know current is a scalar quantity.Is there any special case where we consider current as a vector quantity?Please reply sir.I also enjoy your lectures very much when you say "Have a fun".
In general current is not a vector but in the case of the Lorentz force it is a vector as it is the direction of the moving charges in the wire that counts. F=qvXB. In the case that I discuss here it too is a vector foer the same reason. Thus the unit vector F is the cross product of the unit vector of v (this I) and the unit vector of B.
Thanks a lot to you sir from india🙏🙏🙏
I never noticed until now, at about 4:35, did you slip and say vier? :)
my first lecture but have to say have fallen in love at first sight .
Professor, our physics teacher said that Physics is not just all about solving problems on electric charges and getting marks but its science as a whole is ultimately the way you think. Because in today's world a person without a scientific insight is more likely to get fooled. So he has asked us to get practical knowledge of this topic by studying about its applications in the real world and machines and experimenting. Can you tell me it's direct applications for the undergraduate level so that i can read about those and get some 'out of the book' real engineering knowledge.
Your teacher is RIGHT. I tell students all the time that Physics is not about equations. It's try that Math is the language of Physics, but Physics is about concepts. Think about Faraday's Law which now runs our world economy. Nuclear energy (Einstein) will rescue us from running out of energy. Watch my lectures and you will see countless practical applications.
Lectures by Walter Lewin. They will make you ♥ Physics. Ok thanks professor.
respected sir,one of my teacher told me that in magnets there is only one pole .there is no physical difference between north and south pole both are just only revolving electrons .poles are just perception of observer not the property of magnet but in charge + and - have different physical properties and they are not decided + and - according to place from where they are seen.Is this right to say that magnetic has only one pole,and Gauss law can be stated as 'magnetic fields lines always form close loops.'?
>>>one of my teacher told me that in magnets there is only one pole>>>
wrong
Absolutely loved your lecture sir,😍😍
But I am having a doubt
'what if an observer starts rotating around a stationery charge, will it produce a magnetic field for him as in his Frame of reference the charge is in circular motion and a charge moving in circular orbit should produce a magnetic field???
magnetic fields are the result of Lorentz contraction as nicely covered in Purcell's Book (chapter 5). Yes if you move relative to charges, in your fr of ref there is a current and thus a magn field.
@@lecturesbywalterlewin.they9259 Thank you very much for your reply sir. ☺️☺️
Hello Sir, thank you very much for providing this great lectures. I think I am ready to start building my motor and earn some imaginary credit. In order to start in the right direction, can you give us more details about the size of the magnets and the dimaters of the copper wire?. In the PDF provided it just says two magnets and 2meters of copper wire. Thank you again Mr. Lewin.
I gave this lecture 18 yr ago
Sir , Thankyou for making physics so interesting for me . Sir , I have a question that if the shape of the wire is very complex then is there any other way to find the magnatic field of that wire except vactorly adding them because it would be very difficult to do that . Please help me with that for which I will be thankful to you.
sir, can I remove the effect of experiment done at 24:10 minute( I just did it on my old TV):D
sure
Feel free
47:43 sir the magnetic fields should be from north to south isnt it?
By the way I am grade 10th student from India maybe my knowledge is low in this concept.
But I think the coil should go down.
Sir, At 13:21 you said that above the wire carrying current i1 the direction of magnetic field is out of the black board but you said that direction of magnetic field below the wire carrying current i1 is into the blackboard. I am a bit confused about how are you finding the direction of magnetic field. Can you please clear my confusion.
use Ampere's Law
Sir, what magnets are those? How strong should I go, If I wanna do it on my own?
Dear professor,
the way you draw magnetic field lines at 47.17 makes it seem like the convention is South to Noth. However it is the opposite though, right? Do those lines mean something different? Or is this just a shortcut convention to draw B-field lines
magnetic field lines are all closed loops. If you have a magnet, by convention the emerge from the magnet at its North Pole and enter back into the magnet at its South pole.
Sir your's demonstration helps alot to know physics ❤️🙏🏻 in depth
Regardless of whatever issues MIT has with you, I think you sir are a gift to academia and humanity. I've enjoyed all your lectures immensely and wish there were more professors with your passion and dedication to teaching. I wish I had a collection of all your lectures on a disc to share with my children when they're old enough to benefit. Do you have them on disc or maybe Dropbox?
Alfred Castillo Exactly and i'm proud of this professor from the Netherlands just like i am. You can clearly hear that he has a Dutch accent.
Ernest schoenmakers Yes I was born in the Netherlands. Got my PhD at the TU in Delft in 1965. In January 1966 I went to MIT (2 year post doc position). In June that year I was promoted to Assistant Professor. I never left. I retired as a Professor at MIT 43 years later, in 2009. I still have the Dutch nationality!
To Walter Lewin Uw lessen zijn geweldig en ik steek er veel van op. Je engelse achternaam, is dat afkomstig van de nederlandse Leeuwen of van Leeuwen?
Mijn achternaam, Lewin, is een joodse naam. Mijn paternal grootvader en m'n vader hadden dezelfde achternaam. Lewins vind je overal in de wereld. Mijn DVDs zijn bij MIT te bestellen ldg@mit.edu maar ze zijn ongeveer $25 per stuk. Ik heb 120 DVDs. 94 ervan zijn min cursussen.Ik woon al 50 jaar in de VS. Het is dus onbetaalbaar. Ik ben ondanks dat toch nog steeds Nederlander.
groeten
\\/\/////@lter
Bedankt voor de info en er zijn nog 2 andere fysische professoren die ik goed vind en dat is Leonard Susskind van Stanford University en die Indische professor van Yale University.
why is it that only moving charges produces magnetic field?
The time may come that you will study Einstein's theory of Special Relativity. It shows that magnetism is the logical consequence of moving electric charges. You can read about that in chapter 5 or Purcell's college Physics book on E&M.
thank u sir
@@lecturesbywalterlewin.they9259 But why would charges produce magnetic field when they are not moving and then if it is like that, electron always moves which is negative charge inside the atom. So is magnetic field everywhere around us? Or the magnetic field is neutral inside the nucleus but that couldn't be because magnetic field is produced by moving charges... Total net charge can be neutral and not the magnetic field! So therr are so many electrons around us since every single thing is made by atoms so why is not there a lot of magnetic field? Electrons always move and they are charges after all...
@@Annie-bf9ic charges at rest not produces magnetic field
@@Annie-bf9ic only a moving charges produce magnetic field
That is given by savart law
Thank you sir for this great explanation, can you explain the quantum physics in that way so its vary helpful
Sir I’m a high school student in Turkey. In our country, teacher’s teaching skills are so low they don’t even talk about what magnetism is. They’ll just give you some equations and then they’ll jump into the solving problems. (And I’m not even mentioning schools are too broke, teachers are too careless for showing experiments.) Because all they care about is university exam. Not just teachers also the students are behaving that way too. No one really wants to learn. They just want to memorize how to solve problems until the exam.
But why did I wrote this? *I wrote this to show how much appreciate your teaching skills* When started to learn magnetisms I had bunch of unanswered questions waiting in my head. I still have those bunch of questions but at least some of them answered because of your videos.
Thanks a lot
thanks for your kind note. Stay healthy in Turkey! The number of people there with confirmed infection is growing every day!
23:00, don’t mind me I am just putting this as reference :)
Professor I have a question... We say when electric current flows through a spring it compresses because of attraction due to magnetic force ... But why do we ignore the fact that there has to be some electrostatic repulsion between the electrons flowing in the spring... As since we know electrostatic repulsion is far greater than magnetic attraction in this case... The string should rather elongate... ( This question was asked in jee and I had a doubt in the answer... The answer was that spring would compress when current flows through it)
this is a classic demo - use google for details
sir @3.17 you are telling that in north canada it is magnetic south pole of the earth , but not magnetic north pole?, what is the meaning precisely?, is it means that in compass south pole will attract to morth so it is red colored that's why you are saying it is magnetic south pole ? or what . but in the video you are saying that magnetic south pole OF THE EARTH? or is it compass?... clarify sir
The north pole of a permanent "bar" magnet that can rotate freely inside a compass points to the Earth's magnetic pole in Northern Canada. Thus that is the Earth's Magnetic South Pole.
@@lecturesbywalterlewin.they9259 ok thank you sir. In northern canada , north pole of permanent bar in compass points to earth's magnetic south pole. thank you sir for explanation.
Sir i had a question. When a charged particle moving with a velocity v is placed near a current carrying conductor it gets deflected. Why does it get deflected ? Is it due to magnetic field? Why is there a deflection only when the charged particle is moving because there can also be a deflection due to electric field produced by the conductor.
F=q*vXB watch my lectures.
28:10 literally me during the previous lecture. and i realized the same conclusion.
35:48 the difference between the two currents is mainly an issue when using the right hand rule. for conventional current, it's actually the left hand rule. easy enough.
I started to love the Netherlands as a country just as I started watching prof. Lewin. Coincidence?
One of the best illustrations that make you understand Maxwells equations and the relation to Einsteins theory is the following: Imagine a electrically charged hollow sphere, its electric field E have an energy e and a mass m where e = m c^2( Einsteins equation energy is equal to mass times speed of light squared) . Now let the sphere have a speed v, we can calculate the magnetic field around it B. The energy b of the B field is slightly higher than 1/2 m v^2 so the magnetic field is the kinetik energy of the electric field plus a small contribution that come from the energy that keep the sphere together ( also kinetic). Now the interesting part. Take a rocket and fly next to the sphere and measure the magnetic field around the sphere. There is no B field. So if the sphere has a speed relative to you there is a magnetic field but if the relative speed is zero there is no field. This created some discussions because how can it possibly be. It leads to that time is also relative and Einstein understood that.
really thanks a lot for these great video prof. but if there any videos about permanent magnets which are used in various application. Thanks in advance
:)
27:04 29:26 Is that a drift velocity? 🤔
Should be v{d}= aτ ~a∆t~∆v , then.
But you give it as: v{d}=dℓ/dt...😵
So, is v{d} a velocity or _change_ in velocity?
Also, is it over the same time scale "τ" ?
What is string theory?
don't be lazy, use google
Why we can think as magnetic field produce by constituent particles Magnetrons like the electron-proton and neutron?
Sir, i have a doubt. in the ampere's law , doesn't the d.c current in a wire causes a magnetic curl because the electrons are moving thus causing a changing electric field.
alternatively, if an electric field can cause a magnetic curl, then just a d.c charged capacitor has an electric field which in turn can produce a magnetic curl.
kindly try to acknowledge. I honestly am impressed and motivated by your works. Wish you for awesome life!
DC current does not cause a changing electirc field. Ampere's law (modefied by Maxwell's "displacement current") always holds.
but a charged parallel plate capacitor has a steady electric field in between the plates, but it doesnt has any magnetic field, sir,
could you clarify that sir
Dear Professor Lewin,
at 10:52 you show that wire experience a force that is perpendicular to current and magnetic field. But why does it experience this force? What is happening with the wire that it wants to move?
Best regards,
Tomasz Studziński
I gave the explanation as given in college books F=qVxB but that is not the correct explanation as the vXB force can do no work.
How about tourge? Thinking about if we do not fix the movement of the front againts the mortor or the perpendicular direction. Do you know that some of the fan engine will design to have the tourge direction going into the machine and some in the opposite direction? Electric Fan and Air plane fan will oppose tourge into the front direction while the turbulant in some jet engine will do in the opposite direction.
There is unique of the electric field and manetic field that is why it has effect againts aluminum. If we choose the right frequency maybe it can effect the different metal also. Thinking about the frequency fork and its identical frequency.
20:44 In the name of Nikola Tesla, one of the greatest minds in physics. So much we owe him. You had to mention him, professor.
What is your problem? I mention the unit of Tesla. Just like I use Farad (for Faraday) and Amp for Ampere, Newton for Newton, Curie for Curie. Volt for Volta, Henry for Henry, Coulomb for Coulomb, Gauss for Gauss, . . .,
In 8.01 you used to say something about scientists, when you mentioned the unit named after them. That was a good habit. I just want to point out that you didn't do the same with all scientists. That's it. Sorry for any misunderstanding.
>>>In 8.01 you used to say something about scientists>>>
PLEASE remind me what did I say about Joules (unit of energy), what did I say about Pascal (unit of pressure).,what did I say about Newton (unit of force), Celsius (unit of temperature). Kelvin (unit of temperature), Fahrenheit (unit of temperature), Mach (unit of relative speed), Torr (unit of pressure), Planck units, Just to name a few I mentioned in 8.01.
Such amazing, Nam June Paik was died in the same day (29.1) you was born, Prof. Walter Lewin ( Actually not the same year). When you made this lecture, he was still alived
I have met Nam June Paik several times when he visited me in my office at MIT