8.02x - Lect 8 - Polarization, Dielectrics, Van de Graaff Generator, Capacitors
ฝัง
- เผยแพร่เมื่อ 12 ก.พ. 2015
- Polarization, Dielectrics, Van de Graaff, More on Capacitors, Mystery Demo with Leyden Jar.
Lecture Notes, Dielectrics and Polarization: freepdfhosting.com/a7e868daed.pdf
Assignments Lecture 6, 7 and 8: freepdfhosting.com/73aa29b41a.pdf
Solutions Lecture 6, 7 and 8: freepdfhosting.com/7e11dd8e3f.pdf - วิทยาศาสตร์และเทคโนโลยี
![[UNCUT] ฝันรักห้วงนิทรา | EP.8 (4/4)](http://i.ytimg.com/vi/RDYJYiDwsj0/mqdefault.jpg)
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. Hi sir how are you
Which website?
Sir, Thank you so much for these Lectures, I really enjoy them!
Please, professor, please make sure your videos will continue to be freely accessible after you leave us, we will always need you!
@@andredelacerdasantos4439 when did he said he'll remove?
A brilliant physics teacher who explains everything with experiments .
The demonstration included in this video is mind blowing and simple. This is one of the gems that offers a bridge to connect you to a higher intuition.
A hundred years from now, young minds will see the beauty and feel the irresistibe excitement of physics because of these lectures. They are no less than the pyramids of Giza or the masterpieces of Picasso.
I'm having so much fun just by watching these, I love all Mr. Lewin's spirit, he's the best teacher I never had.
sir , really you are god for billions of students, your teaching is absolutely great and unbelievable good .
:)
@%F0%9F%98%9E/UCiEHVhv0SBMpP75JbzJShqw Sir, thanks lecture is amazing!! But I still don't get that, why needle goes to left in demonstration 3. please anyone?
Billions is a stretch but he is amazing
When I saw that girl sleeping on camera, I had to laugh because she paid $40k to sleep and I paid $0 to be on the edge of my seat.
U r such a clever little boy
You have a wonderful way of explaining information that is often very diffifcult to comprehend; Your Sharing this knowledge with any one who wants to learn and doing so both effectively and efficiantly. Your work is appreciated. Thank you
In this world where ,teacher won't work to show their student real beauty of physics; Prof.walter lewin sir is risking his life to do so.Thank you sir from bottom of my heart.I would have been watching other content that might have taught me the same things but thank god,they all don't even come close to you and your teaching😊
0:54 Dipole formation
15:21 Demo 1
18:20 Demo 2
20:22 Equation set
24:52 Demo 3
29:15 Demo 4
You sire, are a true hero
Thanks, appreciate it
Thank you so much for keeping these on the web! Physics has always been something I've loved....a looooong time ago I watched many of these on open courseware, but that was years ago, much of which went over my head but it was a great introduction. Now taking university level physics it's so great to come back with a conceptual and mathematical foundation and soak in as much as I can. Thank you!
:)
Thank you Dr.Lewin for sharing this jewel with us !
I love u sir for anything and everything u do and speak.
I am learning a lot from u😊
Wish u a busy, healthy and happy life😊
I've had half a century of experience in the electronics field and I have never before had such a clear description of the way capacitors work.
:)
Sir I’m enthralled and I just can’t thank u enough for ur contributions as a soul to the education how I wish u be blessed forver and we can take ur legacy forward
So nice of you
Your lectures are truly a gift!
:)
Brilliant Lectures with amazing experiments. I hated Electromagnetic theory before this, now I can't stop watching your lectures. You are resolving a new mystery in every experiment. ♥❣
Indeed it will take me considerable time to digest those.Sir you are the hero of my world.❤❤
Prof. Lewin has put in SO much work into the demonstrations.....hope the students make good use of the demonstrations. Because, in my experience as a teacher I have faced frustration in the matter. No matter how you put it, science has a high 'intrinsic cognetive load', so, no matter how it is put across, the student still needs to walk all the way to grasp it.....
Thank you professor for the most excellent lectures! You're the reason I am taking this course!
th-cam.com/users/shortsesyw1xihCWk
That was amazing in many ways! Thank you, Professor!
You're very welcome!
This is an amazing lecture, so much important information!
Real definition of teacher
Wonderful lecture sir 😃
Love from India
I understand the Liden Jar like this:
The strong E field between the two conducting bottels creates some corona distrages, so charges go on the dielectric "bottel".
Then wenn you discharges the conducting bottels and put everything back together, the charge on the dieletric bottel (different sign inside and outside) creates a potential difference between the two conducting bottels and thus, wenn you shortcut them, it creates a spark :)
:)
That was a wonderful demostration , I would have wanted to be in that class
what was your explanation?
The glass its polarized, I think, or maybe the base has some charge that its tranfer into the plates
You will have to be wayyyyyy more specific for a proper explanation
There are two cylinders(that previusly I called plates) made of copper ,
1) when the cylinderes are been charged, some of the charge go to the base (I dont know what material it is) so after discharging the cylinders , the charge that was in the base is returned to the cylinders, so can be a potencial diference between the cilinders.
or maybe
2) When the cylinders are been charged, it creates a magnetic field inside the glass, so the atoms in the glass line up with the magnetid field, and when the cylinders are without charge, the magnetid field that is in the glass makes in any way I dont know charged the cylinders again.
or maybe.
3)Everything is discharged ; but when putting back the second cylinder there is friction, some of the charge go to the glass and the other charged its in the the cylinder inside, so when putting near the "promp" the charge the was in the cylinder inside the glass it travels to the "promp" so it discharge it. (I dont know what it name is of the "promp" (I´m spanish speaker))
you are not even close. I do give the explanation + demo in a later lecture. I suggest you watch it.
Wow amazing lectures every engineers treasure
Very nice lecture like always Dr. Lewin, today playing whit the factor K is pushing integrated electronics beyond his limits, in the same circuit we can have high-K materials for high capacitance in transistor gate that ultimate can translate in more speed, and low-K materials for reduce the capacitance between interconnections and have lower noise in the system, all that in the nanometer scale at will, how amazing.
And like always physics works
:)
29:58 this is what I love about these lectures.
Very interesting.A great Prof ever seen.
Happy birthday, professor Lewin!
+Thales Agricola Thank you.
During this lockdown i was really worried how will i do physics when i dont understand a bit of electrostatics. Thx to Dr Walter Lewin not only do i understand it but i also experienced it. Greetings from India
Brilliant lecture sir....love❤️ from India 🇮🇳🇮🇳🇮🇳
Now I am started to love physics... thanks MIT.. thanks for these videos.i love this teaching style.thank you sir..
I'm not gonna sleep tonight for this, really. :D I need an explanation for that capacitor with glass as dieletric! Greetings from Italy mr Lewin, It's my pleasure to watch your old lectures.
I give the explanation in a later lecture.
@@lecturesbywalterlewin.they9259 the dielectric stays polarized after removing two plates then after putting them back in the dielectric induces charge,thats the reason for the E field maybe?
Sir did you given an explaination for this phenomenon. Which lecture can I watch to see that explanation ? Thank you
namasthe sir
lectures are so inspirational, thank you so much
:)
Love for walter lewins teaching from India 😍😍❣❣
You are the best professor I have ever seen. I got an A+ in my class by only watching your videos, didn't even do homework. LOL
"physics is so beautiful...."
Very nice demonstrations in the last third of the lecture.
Glad you liked it
Thank you sir for providing your lecture, its very useful to me ty
:)
That was a good one, Sir.
I'm thinking of my failing A-V sinods.
I was making small videos demonstrating electrostatic charges produced by rubbing different materials. Glass rubbed with silk is supposed to produce an opposite charge on glass than that produced on ebonite/PVC when rubbed by fur/wool. I used two pieces of glass - one made of borosilicate glass, another made of ordinary soda lime glass. The ordinary glass when rubbed with silk cloth was getting attracted to both PVC rubbed with fur, and ALSO to boro glass rubbed with silk....I was scratching my head for a while. Then I realised that the rubbed piece of plain glass was not getting any significant charge (as shown by a pith ball electroscope). It was not charged, it was just showing the dielectric response of getting attracted to both the +ve and the -ve charged object nearby... it was the first time I got to see the dielectric effect of glass, practically. Seeing fine bits of paper flying towards a charged ebonite rod is one thing, seeing a 6 inch long (uncharged) glass strip rotating to follow the ebonite rod is another thing......tributes to all the scientists of 400 years back who had to patiently tease apart the confounding factors to distill Gauss' law out of their experiences in the lab 😊
Hello sir that was a very wonderful lecture and I am very thankful to you for making the concepts comprehensible......
And also, Greetings from India.....
I have a possible explanation for the results seen in the demonstration of the Leyden jar, ( time stamp 40:25 )......
My explanation is as follows....
It could be possible that when you charged the conducting cylinders (thereby making a charged capacitor), the molecules in the glass beaker became induced dipoles......
And when you disassembled the jar setup, the dipoles held on to the charge somehow (I still can't make a clear explanation as to how that occurred, since it was induce)..…
And after discharging the metallic conducting cylinders, and putting them back around the glass (which was holding on to the charges it aquired through the induced dipole), when you connected the two metal cylinders, the dipole charges got a pathway to discharge themselves, going through the metal cylinders and through that device you used to connect the 2 cylinders, which completes the circuit pathway, thus causing the spark, which was actually the induced dipoles getting discharged......
Can this be a possible explanation?
And once again, thank you for such an amazing lecture and a lot of greetings from India.....(I m in 11th standard, by the way, and I still understand mostly all that you teach in the first time........)
HATS OFF TO PROFESSORS LIKE YOU🤯🤯🤯😇😇
This professor is super!!!
Thank you sir I understood all of its concepts
this is what I call lecturing , not like the rubbish universities which just talk like the parrots and do it for the sake of their salary .... walter U bent geweldig dank U , Ik heb 20 geleden in nederland gewoont en ik kan nog steeds nederlands spreeken ,,, you are a legend Sir.
spark between two conductors is due to alignment of dipole in the glass hence +ve side of insulator attract negative charge. nd -ve side of insulator attracts positive charge of conductor. Hence two conductors charged again by the property of insulator i.e dielectric.
you are the best professor!
Glad you think so!
I think maybe charging the plates in the Leiden jar induces a dipole in the glass that stays in the glass when you remove the plates. When you put the plates back they are themselves polarized and because the top of the jar is open, the electric fields don't cancel and a voltage is generated
Great lecture .
in leyden jar experiment i think the energy produced afterwards even after taking off all the charge from the metal plates is due to the charge induced on the dielectric(glass) which then acts as a source for recharging the two metal sheets and produce energy.
If you remove the free charge of a capacitor, the induced charge on the dielectric goes away INSTANTANEOUSLY.
amazing class！
Loved it!!
Thank you very much sir.
The lecture was really intuitive.
The spark between the glass beaker and the copper cylinders experiment may be due polarization of glass. Since glass is an insulator, electric dipoles remain somewhat alligned even after the removal of external electric field. When you reassemble the whole thing, the dipoles induce charges on the metallic beaker which causes spark when shorted.
Not correct.
All capacitors have dielectrics. When you discharge a capacitor INSTANTANEOUSLY all induced charge on the dielectric disappears. Something else is at work here.
The Leyden jar experiment is particularly interesting in the sense that the parts that you think should retain the charge actually do not once it is dissected. The glass jar is prone to holding water molecules from the air on the surface and thus the charge from the capacitor is transferred to the surface of the glass jar via coronal discharge when the system is pulled apart. The charge is then able to be discharged through the conductors when the parts are put back together.
your explanation is incorrect
Lectures by Walter Lewin. They will make you ♥ Physics. Awe shucks. I guess I will have to finish the rest of your lecture series to find out the answer! Still an intriguing phenomenon nonetheless. I do enjoy your lectures! Thank you for taking the time and effort to make them available to the general public.
:)
Lectures by Walter Lewin. They will make you ♥ Physics. I just watched the lecture in which you explain the Leyden jar. I was close in how the charge was conserved yet wrong in the physics behind why it works.
For the full explanation behind the physics I recommend continuing to watch Prof. Lewin's lectures.
como te papeaste una alumna lewin! gran clase
When capacitor was charged, the dipole is created inside glass, while disassembling the device the induced charge on plates got fade away but the free charge dipole of glass was as it was as before so when the device is reassembled the created dipole again induce charge but less in quantity compared to before in the device, now the plates are charged again, hence you can still use the capacitor but with less energy than before. ( maybe i am wrng but i like the demos)
love from INDIA ... :)
prof., in your fourth experiment, you said that in order to compensate for the E field induced in the dielectric, we must add more charge on the plates - so when the dielectric is placed more charge flows onto the plates. but doesn't more charge on the plates mean that the dielectric is polarized more and the opposing electric field is stronger? which in turn requires us to put more charge on the plates? I hope you understand my question.
I have a guess on your demonstration of Leyden Jar and it might have something to do with the metal fork tool you have on your hand: When you remove the inner plates you attach the metal fork to it -> some charges go to the metal fork; Then during the disassembling you again attach the metal fork to the outer plate, it might neutralize some charges on the metal plates but it gains some opposite charges. When you assemble the jar, you used metal fork to attach the inner plate therefore charging the inner plate -> now the jar gains energy again! The reason why I think so is that I noticed that your metal fork has a glass handle therefore cannot be discharged.
no
you are the best.thanks
36:20 Leyden jars discussion!! Yes!! yes! yes!
So if you, a student, had to establish a question from the minute 36:19 - 41:15, what would be the question if you’re expected to answer that same question based on the information given to you from minute 32:5 - 50:09 ?
Best explanation about electricity that I have ever seen (And I am electronic engineer!!!!!! hahahah). Physics works, You are telling us!!!!!!
thank you
Very good lecture Sir. Thanks and Regards 🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏
Most welcome
Just putting my prediction here while I continue the course. The Leyden jar stores the charge on the glass. In a demonstration with Franklin's Bells you can induce a charge THROUGH glass likely for the same reason. Charge is provided to one side, attracts charge from the other. This is why Q is increased with a dielectric, its stored on the surface of it.
you have not properly explained my bizarre demo. I give the correct explanation in a later lecture.
@@lecturesbywalterlewin.they9259 I look forward to it! Hopeful not before another sleepless night.
Thank you very much
:)
Bonjour Pr Lewin, je suis français
Je pense que les charges que l’on retrouve dans le condensateur (Leyden) reconstitué sont les charges induites dans le diélectrique.
The charges in the capacitor at the end are coming from the inducted in the dielectric glass.
so much simple but so much counter intuitive.
this is a good
Awsome lesson. Where do you get your lab equipment like the amp meter, the plate capacitor and the voltage source? I teach and need some lab equipment. Also thankyou for doing this. Your a great teacher. 👍
14:40 I think I may have an other unenlightenment about why the potential difference ΔV between the two plate is growing as we are growing up the gap between them :
As you say at 14:29, E = σ/𝛆₀ , so E is a constant at each point between the two plates, if we grow up the gap, E must remains the same, and since E⃗ = - ∇⃗V and ΔV= ||- ∇⃗V||·d , ΔV between the plate 1 and the plate 2 is getting bigger as d is growing.
Great lecture
Glad you think so!
@@lecturesbywalterlewin.they9259 sir where is optics
Can I get to know in which lecture has sir given reason for the sparks even after disassembly of the capacitor ??
I don't rememebr which lecture - but I did explain it and did a demo to demostrate the explanation
He is an artist look at the board and when he makes lines or dotted lines...
Great lectures !!! I studied physics here in Buenos Aires and i´m refreshing concepts and learning a lot too :-) . I studied this subject from the Purcell book from berkeley and Reitz Milford. Which one do you recommend? My regards to you that made me fall in love with Physics again !!
Purcell is super! Read chapter 5 !
The Liden Jar just blew my mind. My whole life is a lie. I have a midterm tomorrow and I guess I won't be able to get some sleep.
Leiden ;)
My guess for the Leiden jar is that the dielectric is kept polarized and when the conductors are placed again, a surface charge will be induced on them. The top part of the top jar will be +, and bottom part of bottom jar -. Then, joining these to faces with the "wire" will cause a discharge.
incorrect
@@lecturesbywalterlewin.they9259 I saw the solution in a further video. Very interesting Walter! I thought that maybe the dielectric could be permanently polarized - seems not so. Big hug from Spain.
Which lecture did you see the explanation?
23:23 she's sleeping AGAIN! Someone buy her a coffee!
LOL I hadnt noticed. Been watching multiple lectures a day, Walter is so captivating ! How can you sleep!
Yeah let me back to 2004
Ohhh!! I thought she is copying down the notes.
Lol sometimes classes can be boring..
But without this comment..I didn't even noticed it since I'm paying attention to only the lecturer
$27000 for sleeping in class
Thank you very much Sir
Most welcome
Professor how I believe you got a shock at last 😜
Sir, you are right. You only hate physics when you have gotten a bad teacher. Otherwise, it's the most interesting subject. Hats off to you sir.
Sir , your lectors are very helpfull for me so thank you so much
i'am a moroccan student and we learned that we use in place of KAPPA we use EPSILON r which depend on the material
my question Sir , is it the same thing ???
HAve a good day Sir
www.britannica.com/science/dielectric-constant
thank you so much Sir , it really helps
Thanks again :)
The Mystery With the Leyden Jar.
I have an explanation.
The dielectric inbetween has dipoles randomnly aligned. So, when Prof. Walter Lewin charged the plates, they aligned and for that dipoles to be aligned, the electric field does work which is stored as potential energy in the dielectric. Although he disassembles and discharges the plates, the dipoles still remained aligned (he didn't disturb the bottom part of the dielectric). So, when he reassembles that discharged plates, it is the charge density in the dielectric that creates spark. My guess is that, if he hammers or does any physical change to the dielectric while that period, then energy mustn't be left.
Although he left the dielectric down, some may think charge might've flown. But the table is wood!
Prove me, if I am wrong or right.
I give the explanation in a later lecture
So irritating when it zooms onto a students face when he is trying to speak about something on the chalk board.
Thomas rad Nah you get to see the beauty of MIT xD
Those are moments where the professor accidentally spoke something incorrect...
They edit those moments out..
@@CrazyGamer-xi8rf you hear the voice man
Hello, Prof.Lewin, at 44:26(you say we do positive work), if there is no E field inside the Van de Graaff sphere, what force is repelling us to bring the charge inside the sphere? Thanks.
there are 2 issues here. 1. energy is needed to place charge on the belt 2. energy is needed to rotate the belt. 3 There is E-field between the belt and the metal "comb" *inside the dome* which removes the charge from the belt
So does this mean the mechanical energy used to rotate the belt is partially converted to the electric potential energy of the charge near the metal comb inside the dome? what I am thinking is something like lifting up a ball, where the work done by us against the gravity is converted to potential energy of the ball. I don't know if there is any similarity between these examples. On the Wikipedia page, it says "The larger the sphere and the farther it is from ground, the higher will be its peak potential". So I think the gravitational PE is related the electrical PE for the Van de Graaff generator. Is this correct? Sorry about this long message. And thanks again for the quick reply.
Assalamoalaikum. My suggested answer is may be it's glass whosemolecules get polarized and make a field. And when inserted again, this field again aligns charges in plates. Right?
(@ 15:45) Prof, what would happen if you just kept separating the the two plates? How far can you go until something breaks down? In theory, voltage would just keep increasing I guess, but to what point?
What type of source was the one you used to transfer charge via the sphere to the inside of the metallic can (in the end of the course)?
At 42:51 why doesn't all the charge transfer on to vandfegraph and on the second time itself both would become equipotential?
Hello Dr. Lewin, at 18:30 you put the 7mm glass between the two plates and then take it out, there is expected to see no current through the amp meter, but I see the amp meter moved a little bit when the edge of the glass is going in and out of the area between the two plates. In addition, the amp meter goes towards two different ways when the glass is put in and taken out. Would you please explain this? THANK YOU.
The amp meter is doing exactly what it is supposed to do. Please figure it out!
I think the little move of the amp meter is caused by the little bit current which is flowing towards the propeller volt meter and back. Am I getting it right？
Lectures by Walter Lewin. They will make you ♥ Physics. I do see a tiny bit movement about the amp meter too. I think it may caused by the creation of the induced electric field which has opposite direction and creates a temporary weak current going through the amp. May I have your opinion sir?
Sir what is the answer to the question you posed with respect to the capacitor still having a potential difference after you clearly removed the charge?
He explains it in a later video
When I saw that women sleeping at 23:20 , I had flashbacks of me trying to stay awake during this class🤣🤣🤣
sleepy girl at the back!!
@Lectures by Walter Lewin. They will make you ♥ Physics.
Why an induced electric field, in the direction of the applied electric field, not created by the dipoles inside a dielectric when placed in an external electric field, as the direction of the dipole, induced field, and external field will be same?
please anyone explain
Thanks, Prof. Walter Lewin for the great lecture. Could you please explain about the probing you used for the Van de Graaff voltage measurement? One side of the probe is grounded and the other side is on a distance from the Can you are adding the charge on? Thanks
your question is not clear. Refer to how many minutes into the lecture and then rephrase your question.
@@lecturesbywalterlewin.they9259 Thank you very much for responding and sorry for the unclear question I had. Actually, what I was referring to is the following: you examined your own Van de Graaff with a paint can and measured its voltage using a voltmeter as you were accumulating charges on the paint can. To measure the electric potential difference of two points, I think we need to connect both probes of the voltmeter to the two points. But what I was seeing in the lecture video was that one of the probes of the voltmeter was hanging on the air, close to the paint can, assuming the other probe is grounded (Maybe I don't see it well, though). Is that how should it be?
@@rezamaram2439 if you want to know the details of how we measured the potential contact Andy Neel aneely@MIT.EDU
@@lecturesbywalterlewin.they9259 Thanks a lot. I certainly will.
Perfect
The reason behind Walter Lewin holding his head while touching the charged Vandegraff is to direct the current through the hair(shortcut the body) so he is safe.