Lec 14 | MIT 8.02 Electricity and Magnetism, Spring 2002

[shellybirdy]

brilliant video

[bebeheuy]

I Love The Video It Can Increase My Knowledge Video Biot-Savart Law,Gauss' Law for Magnetic Fields,Revisit the "Leyden Jar",High-Voltage Power Lines

[Mjhond]

Steady I Really Like This Video Biot-Savart Law,Gauss' Law for Magnetic Fields,Revisit the "Leyden Jar",High-Voltage Power Lines

[moejobe]

@15:26 LMAO. listen carefully

[hardways33]

49:54



[nanjingian]

I think this professor is great, I wish I could have had his lecture.

[Milchi7]

best physics teacher =P

[mdgreg]

Is Most of the Energy Storage in the Distortion of the Molecules in the Glass, and Not "Free" Charge On the Glass?

[OKMUNWURX]

The charged glass demo has me thinking about electrons and holes being rearranged and so trapped in the glass when the electrodes are removed (then replaced). Electret condensers use this trick too.

[moonfiber]

we meet again, 240p

[zeeracer21]

@lenlen1010

DUDE what the hell do you think of your self eh ? Dont you have some respect for Walter Lewin ? do you even know his achievements ? His experience and the vastness of his knowledge ? You say you have worked with physicists 20 times smarter ? eh ? I doubt it. You wouldnt have sounded so DUMB if that was true.

Seriously get a life , Get over your arrogance and Learn. Be open towards learning . No one knows everything okay ? and no one is 100% percent correct always. And you are one .

[lenlen1010]

@zeeracer21 I am not obligated to show respect to someone who starts insulting me for no good reason, he may know how to inspire students but his grasp on physics is only impressive to a young student, almost all physicists I've worked with put Walter Lewin to shame.

Pot-logic never ceases to amaze, you say "No one knows everything okay ? and no one is 100% percent correct always" yet you sound very confident in your position.

[MarcoOrBust]

i feel like this guy inspires with the smallest notions through out his lecture

[MarcoOrBust]

@walterhglewin i made a fool of myself by saying the professor inspires his students? i think you misinterpreted my comment. dont be an ass

[walterhglewin]

@MarcoOrBust Sorry Marco, my note was meant for lenlen 1010. I apologize for having accused you for something you did not do. I removed my note to you and sent it to lenlen 1010. greetings,

\\/\/////////@lter

[LeibelMorosow]

To expand on my post of 4 days ago, unlike the charge on say a sphere, the charge on the outer surface of this glass is being firmly held in place by the opposite charge on the inner surface of the glass, and just like with any capacitor /Leiden jar both charges must be removed simultaneously, had the professor realised this he wouldn't have had to use his shirt

[lenlen1010]

@LeibelMorosow Wow, you're right, MIT really needs to trash the entire last three minutes of this lecture, they need to rerecord a new version, they also need to give you an acknowledgment.



[walterhglewin]

@lenlen1010 You made a fool of yourself. Before you make some arrogant statements like you did, you should first learn some physics. When you know soooooooooo little, you should be more modest. LeibelMorosow was dead wrong, his knowledge of physics is equally poor. You can read my replies to him. He does not understand the fast difference between the behavior of a conductor and a insulator. Glass is an insulator. You would be well served to delete your ridiculous comment.

[lenlen1010]

@walterhglewin I'll have you know I've worked with physicists that are twenty times smarter then you and no one has ever called me a fool, you are calling me arrogant, why don't you go look in the mirror, LeiblMorosow made a very clear and valid point which from your answer its obvious that you didn't even bother reading before you started hurling insults, you obviously are in love with your own voice and incapable of hearing anyone else, you sir are an arrogant self absorbed individual.

[LeibelMorosow]

Great lecture but in the last five minutes when he tries to remove all the sprayed on charge from the glass, he has a hard time because he is doing it wrong, he is forgetting that the glass is still a capacitor - since charge doesn't travel along the surface of the glass the glass is actually a bunch of little capacitors - and the only way to remove charge from a capacitor is to touch both sides simultaneously, touching one side at a time gives you noting.

[walterhglewin]

@LeibelMorosow Most capacitors have two metal surfaces separated by a dielectric. If you do not exceed the maximum allowed voltage there is no net charge on the dielectric, there is only "induced" charge on the two surfaces, but the net charge is zero. If you did not exceed the maximum allowed voltage, when you remove the charge on both metal plates the charge on the dielectric should remain zero, and the induced charge at the surfaces of the dielectric disappears instantaneously.

[walterhglewin]

@LeibelMorosow With the Leyden Jar I purposely exceeded the allowed voltage by a large factor and that sprayed charge on the dielectric. Thus when I remove the charge on the metal plates, there is still net charge on the dielectric (which produced the spark). However, when I also remove the charge I sprayed on the dielectric, there is no spark. Glass is a good insulator; it's not easy to remove the charge. Some readers have a misconception about dielectrics. I hope they do understand it now.

[walterhglewin]

@LeibelMorosow I'd like to add, that if I had not exceeded the maximum voltage when charging the Leyden Jar, the net charge on the glass would have been zero. There is induced charge on the surfaces of the glass (of opposite polarity). That charge is there ONLY as long as the glass surface is near the free charge on the metal (remember it is induced charge). If I then had removed the metal from the glass as I did in class, the induced charge on the glass would have disappeared instantaneously.

[walterhglewin]

@LeibelMorosow You are confusing the behavior of conductors with that of insulators. If I have a glass slab which is charged (free charge) at both surfaces (with equal and opposite charge - which all by itself is IMPOSSIBLE), and if you then touch both sides simultaneously, you will only remove charge located at the position where you touch (thus you will remove only a very small fraction of the total charge). The reason is that a dielectric is a very good insulator.

[LeibelMorosow]

@walterhglewin Ask yourself the following two questions: 1) approximately how much energy would it take to distribute a micro coulomb of free negative charge over a given glass slab. 2) approximately how much energy would it take to distribute two micro coulomb of free equal and opposite charge on both surfaces of this same slab. (the former divided by the latter equals THOUSANDS) therefore the latter is NOT JUST POSSIBLE IT'S AS COMMON AS CLOUDS THAT HAVE COLLAPSED INTO STARS.

[LeibelMorosow]

@walterhglewin Also, you repeatedly mention the three-million-volts-per-meter rule for air, so haven't you ever wondered why you can't remove the vast majority of the multi kv charge from the jar's surface with just one sweep of your fingers???

[Danthaman1971]

Gold has actually a higer resistivity than copper (2.2 x 10^-8 for gold and 1.67 x 10^-8 for copper). For high voltage cables usually it's aluminium that is used and then gold would be better (2.65 x 10^-8 for aluminium)...

[farestabs]

This man is brilliant, and I very much admire him for that.

[Majutube2010]

VERY GOOD I LIKE IT MATHOD WHAY SYSTEM

[FlavoredCoffeeGuy]

I noticed with a TV tube how hard it is to get ride of a charge on glass. I actually found that you can pump electrons through it and build up a stronger electric field. Turning the TV on then off on off long enough for the tube to light produced a much higher charge. So, there had to be some charge layering wihtin the glass.

[gspradoneto]

brilliant class.

oh, magnetic monopoles are not so far from being manufactured, you can the theory becoming fact in several recent articles published, as this one published recently buy guys from the Imperial College London in UK.

[PointOnACurve]

Convert the Electric energy to Light, move it, then turn the light back into electric potential.

[quantomic1106]

hey I got an idear!

[akhiltuffy]

this guy just finishdteaching me a chapter which would have taken me atleast 6 hours in 50 minutes :O

[MiriamUpdate]

he says "IDEAR" lol

[1987dman]

how does he make those dotted lines on the board with that chalk he has?

must be some expensive high end chalk.

[1kingconan]

THERE IS A TECHNIQUE, IT'S SIMPLE

[1987dman]

please explain.

[shim2dawg]

@1987dman no it isn't

he's just pushing it along in a different way

[1987dman]

someone call the ambulamps.

[xbeerxpressurex]

@1987dman LOL!

[odem22]

i never liked physics...but because of u i adroe it :D ur such a genuis!!!

[driftx2]

how does he make dotted lines with his chalk? it looks so effortless

[podunkest]

I think he's just angling the chalk completely opposite how you would if you were writing with it so it kind of bounces along the board as you move it. Kind of like \ vs. /

[FlavoredCoffeeGuy]

This makes me think of solid state dielectric pumping to produce ultra high electric fields. Like the one that knocked me over. One flat conductive plate in glass and a ring of metal all embedded in glass at about the distance of the plates in the lyden jar. Corona pumped discharge constructing a series aiding condition in a dielectric. That or stacking glass plates experimentally after having been charged. I want controlled charge migration.

[g0rk3mm]

my professor also told me in

[JerichoKaren]

The electric field stength is strongest at the high radius of curvature. Is magnetic field strength also affected by sharp edges???

thanks MIT!

[cheetah219]

yeah i think its 0

[nepoereh]

This course is beather then my Romanian ones

[easyaspeace]

this helps so much the night before an E&M exam

[matthewcharder]

@easyaspeace funny

[MarZoeKi]

thanks a lot for this video ^_^

[Abba2six]

Haha, my professor gave the exact same line about finding a magnetic monopole and getting a Nobel Prize. I wonder if every physics professor says that. This guy does explain things a lot better than my teacher though. I guess that is why he is at MIT.

[saq05]

my professor said the same exact also!!!

[Shawn3340]

they were classmates in back in college

[AntDX316]

maybe every top college much teach it or else their students wont have everything Top Notch

[hannibal305]

Mine Too =P