Lec 8 | MIT 8.02 Electricity and Magnetism, Spring 2002

[agapitoflores001]

Interesting way of presenting the lessons.

[thebigfootme]

good job! great lecture!

[1PeaceNation]

this lecturer is good!

[plancknplant]

48:12

"and then came van der graaf and he said «look, man, you gotta go inside!»"

hahaa

[havoc4571]

240p we meet again...

[hgfuhgvg]

Is that a banana stuck to his pocket?

[yGorevideos]

SCREAM! SCREAM FOR THE PHYSICS PEOPLE!

[canyknoxville323]

I am starting to hate my prof.

[digicho]

Well, great job! But missed some demonstrations which are really interesting.

[bigshel99]

Here's a guy who knows he stuff and enjoys teaching. Seems to be very well planned in his approach and uses a good mix of lecture, real examples, and some excitement to keep students brains working.

[jackillac92]

That guy has a funny accent, some chalkboards and he knows how to use em.

[Compact3]

I don't understand something:

if you keep Qfree stable, but you increase d then V will go up he said (and showed).

Does that mean that if you make d a few meters that you have several millions/billions of volts? Isn't that weird? Does that mean that if you connect the two plates with a resistor when d is little then nothing special will happen, but if you connect the two plates with the same resistor when d is big then the resistor will melt? Wtf?

[cyorks90]

@Compact3

Remember that V=E*d. The units of an electric field are N/C and V/m (Volts/meter is what you should think about in this case).

As you increase the distance between the two plates, you are doing positive work and you are increasing the potential difference between the two plates. He is talking about the case where the plates are close enough that the electric field remains constant. However, when the distance between the two plates increases significantly the electric field is weaker.

[cyorks90]

@Compact3

The capacitance of a parallel-plate capacitor decreases as you increase the distance between the two plates, but that doesn't matter if you keep Qfree stable, as he said. Think of it as two finite nonconducting sheets with a fixed charge sigma. The electric field due to an infinite nonconducting sheet is sigma/2*epsilon. The sheets don't have infinite area, but if they did, you would increase the potential difference V as the sheets are pulled further and further apart.

[cyorks90]

@Compact3

Once the plates are far enough from each other the plates can be considered point charges. Once this happens, you can find the potential with the equation V=q/(4*pi*epsilon*r).

[amrosik]

@Compact3

you wrote: " Does that mean that if you make d a few meters that you have several millions/billions of volts? Isn't that weird?"

no, look what i am saying: suppose you have no plate capacitor, but a sphere-capacitor (because its easier to unterstand). so you have 2 charged spheres, just like you had 2 capacitorplates... soppose you increase the distance to infinite, that doesnt mean that you have tremendously increased the voltage to billion or something, (continuation...)

[amrosik]

@Compact3...that means,that the ONE sphere has arrived at his maximum voltag that the charges on it create in this spherical object, its like having ONE sphere alone (since the other is infitly far away). and what is the potential in ONE sphere alone with respect to the charge?not billion! its the potential of a charged sphere (lecture 4 i think)!

ok, one problem solved,but you have another problem

a full explaination would take too long,i hate this limit,if you want to know the rest, write me

[amrosik]

@Compact3 what i am saying is, that by increasing the distance, its like disassembling the two plates, and because they are not infinitly big, disassembling means: having two charged objects which are indepentend from each other.

[7kholoud]

whts up with the bananas and donuts he puts on his shirt??

[savinay1983]

Who wouldn't want to see their professors take 30,000 Volts? I love this guy.

[xKorax]

@savinay1983 yeah but the camera's missed the moment he touched it -.-

[xKorax]

@xKorax ops cameras*

[rahulilrplac]

I think that spark happens because of the glass.

When the circuit is complete and some charge flows into and out of the system, the Glass also gains some charge. When the final reassembly happens, the charge on the glass induces some charge on the capacitor, and hence the spark.

It's a wild guess. Can you guys comment on this?

[cyorks90]

@rahulilrplac

That's what I'm thinking too. Glass is an insulator, so some of the induced charge on it will remain in place. This phenomenon is known as hysteresis. When the capacitor is reassembled, the dielectric will induce a charge on the metal and hence a potential difference will be present. The electric field on the plates will be equal to the electric field on the glass.

[jljoljljol]

@cyorks90 what I cannot understand is that how did he touch 30000 v without being hurt? I think he did that at the end of the lecture but the camera did not show that.

[electrostaticaids]

Great lecture, thanks a lot!

[luzzie9]

Amazing teacher. This is more entertaining than avatar and you are actually learning something.

[LogicalFlawDetector]

@luzzie9

Do you even understand the mathematics of this class?

[henf5671]

@luzzie9 well avatar wasn't that great. but professor lewin's lectures are actually more entertaining than anything imaginable that would be classified as entertainment on this planet.

[yoyaya007]

@henf5671 avatar was not that entertaining .... well that's only ur point of view!!!

[henf5671]

@yoyaya007 i never said avatar was entertaining. read previous comment one more time. i said walter lewin's lectures are a lot more entertaining than anything else that would be regarded as entertainment.

[yoyaya007]

@henf5671 what u said was``avatar was not that entertaining`` and i said that's only ur point of view (because i completly disagree , avatar was a real success !!!)

[Mattprole]

I love how we occasionally get reaction shots from the audience. Ha ~_~

[Ribban7]

Great lecture, thanks a lot!

[joelmartens]

Kappa is the same as the relative permittivity right?

[phatl12345]

haha man im starting to view this guy as a celebrity. Such entertaining and unforgettable lectures !

[shinunojutsu]

48:33

IT'S OVER 9000!!!

[azizrezai]

30:11-31:04

"Approach it in a very Cold Blooded Way, Real Classic MIT Way"

I just love this man's style of teaching. The physics society should not only award his as the best lecturer in all the universities but also award him with a Nobel Prize for his work on X-Ray Detection from high altitude flying balloons.

[goodluckpeace44]

he is an absolutely beautiful human being. All gods in the world may protect him.

[FlavoredCoffeeGuy]

Why doesn't anyone just use an electron gun to fire electrons into a metal sphere?

[Axmedkoole]

I didn't know Albert Enstien taught in MIT.

[kloum291]

I no longer need to attend the electromagnetism lecture that I take. This guy is an amazing teacher.

[diomedes39]

He's the best professor I've ever seen.

[diomedes39]

not at all. physics is the study of how the world works through the scientific method and describing that world to make predictions. when was the last time Kant or Descartes made predictions? besides whatever replaces these theories would still be physics, just a newer, more correct version. Science literally begs to be replaced. if it didn't then it wouldn't question itself or reward new ideas.

[bucles2000]

Give me an e-mail adress and I will show you an absolut proof of the logical universe based in 4 axioms and 4 rules of inference using just classical Newtonian mechanics. Then I will show you 2 amazing experiments based in this new deductive method.Inductive method is very important but deductive one is infinity more. If you think a physic experiment or phenomeno is going to change again your axioms its means your deductive method is wrong but not the deductive method itself.

[diomedes39]

Your first words were, "give me an email address..." you may use youtube's pm system but nobody here gets my email.

[bucles2000]

How am I supposed to send you 5megabites of information(54 pages) through youtube?

[Mattprole]

The ideas are not valuable in so much as they are permanent descriptions of reality (after all, science is in constant flux), but rather to teach us an affective method of analysis. It's really just the application of mathematical / logical principals concerning specific phenomena.

[landin048]

What a fabulous instructor.

[Likhi]

i like his banana pin :D

[panzarw]

I so want to go to MIT....

[Saskachewan]

But what about that Leyden jar? He didn't explained why it still had a charge.

[killabilla]

it could hold more charge becuz of the dielectric material

[Saskachewan]

That's not the case. I asked about why the Leyden jar holds its charge even after decomposition and discharging the metal plates.

I've found the answer in one of subsequent lectures: charge escapes from plates to the surface of the dielectric jar during decomposition due to the corona discharge effect and stays there instead of the plates.

BTW I don't know why someone gave me thumb down for that question ;/

[radioam232]

As far as I know from radio technology the charge on the plates of a capacitor (also a Leyden jar) always fades away by a certain time, as it is discharged through the air. This can last a very long time, dependent on the quality of the isolation, the amount of charge, the space around the capacitor.

[NinjaAnimeNancy155]

great