Lec 10 | MIT 8.02 Electricity and Magnetism, Spring 2002

[bladervinay]

A very good teacher who explains things quite clearly and you can see this guy has the passion for science or physics

[Kricardose]

I am very happy to see the vidoe Batteries EMF,Energy Conservation ,Power,Kirchhoff's Rules,Circuits after you give this

[bebeheuy]

I Love The Video It Can Increase My Knowledge Batteries EMF,Energy Conservation ,Power,Kirchhoff's Rules,Circuits

[Mjhond]

Steady I Really Like This Video Batteries EMF,Energy Conservation,Power,Kirchhoff's Rules,Circuits

[NorineJunkovs678]

ehm ich bin eine gummi puppe

[apheus27]

The sulfuric acid will boil, the case may melt, and that's no good. Lmao

[brianwesleyan]

Trippiest part: 39:26

Uh oh!

[mdgreg]

Can the Water, In the Final Demonstration, Be In a Contibnous Stream From Top to Bottom? Is the Water Conductive or Nonconductive?

[CuriousKirchhoff]

You awakened the love & interest for Physics inside me :)

[Top3percent]

And if you go 80 mph, you will teleport!

[Top3percent]

Doc Brown?

[weweallthewayhome]

omfg he teaches so well it makes me angry :(((

[blabla791]

i don't understand why the SO4-- travels "uphill", opposing the electric field. Is it because it prefers Zn++ over Cu++? Is the Zn++ attracting it that badly?

And what's the need for SO4- in the Zinc basin at the beginning?

[kotofu]

explanation to the Kelvin Water Dropper in lecture 15. Start at about the 28th minute. Enjoy!

[ryry46d9]

@kotofu

44min not 28

[kotofu]

@ryry46d9

I am talking about lecture 15, the revisit of the Kelwin Water Dropper. In this lecture, he does not explain the way the battery works, he is only showing what it can do.

[Paladin1warrior]

@kotofu That's what he said. He said that is a quantum physics question when you ask how a battery works. You get a brief explanation in University chemistry class.

[13Septem13]

Guys it doesn't matter at which grade or uni you study something....It matters if you understand it and using it.

[LegendLength]

@13Septem13

Exactly. I've seen software developers with *masters* degrees and 15 years of experience who still produce unusable spaghetti code.

What matters most is how much you think about the subject and the depth of your understanding. Knowledge alone is necessary but understanding makes the difference in the qualify of your work.

[Funyima2010]

the battery you showed at the end, is it because of water being a bipolar molecule it induces the buckets that when sufficiently exposed to the polar H20, causes the development of pd.my guess is that the buckets a and b are of different material, thus resulting in difference of the polarity. the reason for the water to sprayed out: the interaction between induced charge on the surface of A/B with the polar H20, the induction influences the tip of the tong and causes a spark just like thunder

[mdinka]

@44:03 why did he choose to draw the direction of the current I along the CCW path of the circuit? Wouldn't it be also possible to take the other CW route? I.e the shorter direction between + and - ?

[mdinka]

@mdinka sorry, i meant @00:44

[circusboy90210]

glad to see you are still keeping with this. don't stop when you are bored with what you feel is remedial, it will reinforce your knowledge for when things get complex & you are grasping @straws again failing your basics.

[LegendLength]

@circusboy90210

Strangely I found the first couple of lectures the hardest, although they were still fun to watch.

[kidmystik101]

Anyone else catch the asian guy sleeping at 31:24?

[sylfix]

@kidmystik101 he is not sleeping thats how asian's eyes look like.

[treven314]

Requesting a HD video of a car battery being shorted out for a long time. I have not been able to find one yet on youtube.

[mrgzcreations]

everytime when I see a mistake I pause the video and open up my email to contact Mr.Lewin so that I can talk with him, but when I go back and play the video to reassess the mistake I find out that it has already been corrected and I miss my chance to talk with him :(

[darat23]

I wish I had teachers like this when I was in school he is the best teacher I have ever seen.

[royalsnowman]

But still, he is the best physics teacher in the universe

[royalsnowman]

Oh no. He got mixed up with the Kirchoff law. It should be the other way round. Anyone disagree?

[MrJavaHelp]

@royalsnowman yes i disagree bigtime

[afdhalatifftan92]

Help! Wasn't it the E symbol meant electron flow? Why did the prof. say it's electric field?

[Mattprole]

As far as I can tell it's always been Electric Field. Electron flow would be current, denoted by capital i

[royalsnowman]

Sorry, but you're incorrect. Current = flow of positive charge.

[trentib69]

@royalsnowman actually it's a negative charge protons are to heavy to travel. it's actually the electrons do the traveling... from negative to positive... that's the physics of it anyway

[royalsnowman]

@trentib69 Physically, you're right. Electrons are the ones that are moving. However, a negative charge moving in a direction is mathematically the same as positive charge moving in the opposite direction.

[kirbuschrist]

@royalsnowman Current flows from negative to positive.

[royalsnowman]

@kirbuschrist There are two currents --- Conventional current is + to -. Electronic current is - to +. Sorry, forgot to add the word "Conventional" because most of our current that we're dealing with are mostly conventional ones

[teledynepost]

current is capital I.

E is electric field, not electron flow.

[ncbookz]

i = current, e= emf = voltage

[lovbinfr3sh]

@ncbookz doesn't the voltage = potential difference?

[GunsNRosesbitches]

@lovbinfr3sh yes

[tkshoe]

that chalk is so awesome...

[Airmack]

Wrong!

The network is definetly assymetric, this nullifying your assumption above.

In the above network the following assumption might be true: V1 has a higher potential than V2 and R2<< R3

Check out assignment 3.7

[CrazyScience]

If V1 has a higher potential than V2, then it charges battery V2 (energy transfer, like capacitors). But, in this case, current can't flow at battery V1 as is pointed above.

Okay, let's say that problem is solved, and that for sake of preventing algebraic headache, you are correct.

In assignment 3.7 I found even more complicated circuit, with three batteries and five resistors. "More food for 'algebraic headache' ". ;-)

[CrazyScience]

Is that only me that noticed error after time [38:16] (in explanation about Kirchhoff law), that current from the left battery is pointed in wrong direction? It should be counter clockwise, or from plus pole of the battery, through the series resistor to the minus pole of the same battery. I think also that because of that, math is also wrong.

Anyone else noticed that?

[Airmack]

It is not wrong! In the end he says I1 is negative ...

At the begining you define your I in one direction , but after solving the equations you might find out, that the current flows into the other direction (negative sign)

[CrazyScience]

If we assume that current flows according to arrow (pink chalk on blackboard), then yes: I1=+3A, I2=+1A, then I3=3-1=2 (+2A).

If we look at the battery orientation, then I3=3+1=4 (+4A). That is huge difference!

On second example, if: I1=+1A, I2=+1A, then I3=0, ONLY !!! if we follow that pink chalk arrow, ignoring REAL battery orientation.

If we ignore wrongly drawn arrow, then I3=2A.

[CrazyScience]

But, that is not my point. Look it at this way: Almost 30 000 views of this video, but ONLY ONE (me) dare to complain about that confusing error.

So, for ~30 000 ignorant people, everything is just fine - but, only one complains.

Statistically looking, that is negligible number of people who dare to complain about something not so important in our everyday life.

[CrazyScience]

Now, imagine how is easy to manipulate with mass of people over the media (newspapers, TV, radio...).

Imagine that over the internet you CAN complain, and maybe someone will agree with you, because of possibility of 'two way communication'.

But, if you look news on your TV, newspaper, or listen radio, you CAN'T complain, because nobody will agree with you, and you know that very well.

'(Al)mighty people' behind TV screen are well aware of that, so nobody care if you are misinformed.

[Airmack]

The things you are saying are still wrong. There is no difference in which way you draw the flow of the current. As can be easily proven

equation from prof.:

I1-I2=I3 = 3A-1A=2A

Equation with I3 in other direction :

I1=-3A

I2=1A

-I1-I2=I3 = 3A-1A=2A same as above.

As i said, IT DOESN'T matter how you draw it. The equations show wether you drawed it 'wrong'.

Your battery orientation, isn't worth anything, as there might still go some current through one batt due to a high potential of the other

[CrazyScience]

But, all the time we are subtracting current, which is more confusing.

Let's then calculate sum of currents.

I1=(-3A), I2=(+1A)

Then: -I1+I2=I3 = (-3A)+(+1A)=(-2A)

That is only if current flows as pink chalk points. Note that from battery V1, current flows from minus to plus (it can't be!), but from battery V2 currents flows from plus to minus (that is correct).

[CrazyScience]

If you look at "real" battery orientation, and know that current flows from plus to minus, then:

I1= (+3A), I2=(+1A)

And:

I1+I2=I3 = (+3A)+(+1A)=(+4A)

---

Let's imagine two batteries of 1.5V, R1, R2 and R3 are three equal light bulbs, then try to connect it as is shown on the diagram. In one case, light bulbs R1 and R2 will glow, but R3 will not.

Reverse just one battery, then R1 and R2 will glows equally, but weaker than R3 - which will glow with sum of crts. from R1 and R2

[Airmack]

Buddy , your math is terribly wrong here:

I1=(-3A) => -I1 =3A but you state that it is -3A which is obviously wrong

[CrazyScience]

Oh, yes... my fault. You see - I got an 'algebraic headache'. :-)

Now, I see why people not like think about that or similar problems.

[pornopolitik]

I'm watching these videos instead attending my own college's course and learning better.

thanks to MIT and Youtube from Turkey

[freezzertime]

outstanding professor.

[tengoliver]

does anyone know the theory of the final experiment? that is interesting

[stradijeri]

It's called the "Water Drop Experiment" by Lord Kelvin, or "The Waterthread Experiment" by Viktor Schauberger. Have fun googling :)

[UserIsAnFBIAgent]

Awesome, I'm going to school to learn about electrics at MIT, awesome.

Currently I am learning about Capacitors, Resistors, and NPN Transistors, and PNP Transistors.

This is some heavy duty stuff, thanx MIT and YouTube.

[goodluckpeace44]

thats good good luck.

[waterpowerisreal]

this guy is cool i think.

[fandennis]

23:34

[heltonsouza247]

Eu sou técnico em eletrica aqui no Brasil e esta aula é demais!!!! Very Good!!!!

[mademedoit]

I dont know... how is a laptop my supply. And how is the resistance infinitely large when it isnt there..

[celisto001]

This is amazing how in depth it really gets, my plan is to go to MIT for engineering, but this is interesting!

[lowfat422]

I short circuited a car battery before and let me tell you...I almost wield my hand on the car battery, along with the wrench. To make matters worst, it was raining that day (don't ask). Me = stupid. Yes.

[petethepotato]

Shame that he's picked up that students (and instructors) often say "battery" when they mean "cell". But an excellent lecturer nonetheless.

[LegendLength]

@petethepotato

It's a single cell battery.

[apparent123]

The best point of the lecture was:

Partner produces heat as twice effective as an electrical blanket.

So use a partner when u wana go to bed in winters.

[gamesguru]

"So a partner is about twice as effective as an electric blanket. Maybe also more fun."

LMAO. It's even more funny when a guy like him does that.

[epicvelocity]

Wow...isn't this kid of basic for MIT? Here in Quebec we do this in grade 10.

[metalminded]

hows the spelling classes in Quebec?

[epicvelocity]

Obviously vastly superior to the grammar classes where you live.

[epicvelocity]

...Wow. If you really are an MIT student, which I doubt you are, you're spelling and grammar is frankly pitiful, meanwhile, I make a typo and I'm the idiot? Please get a life...

[epicvelocity]

OH! Sorry! ***your spelling and grammar classes!*** -.-

[VenomFangXposed]

metalminded what a load of shit us Americans could only dream to be Canadians.

[rkt739]

You guys are really weird. And everyone knows it's the University of Chicago students who can spell and grammatize. :p

[celisto001]

owned!! Indeed, you're metal minded, so we see americans have such limited mind..

[goodluckpeace44]

John Nash was a American

[Dynamics18]

you guys are really weird. O_o. everyone knows that some people sucks at grammers, regardless of where they take classes.

[jsymons1985]

I think it gets a little harder

[acerie]

I am an American doing studies in Switzerland. On top of the language barrier, I have a lot of professors that are great researchers, but not so great in the classroom. This guy is saving my grade. THANK YOU MIT

[jonahansen]

Yes - he's very good, isn't he?

[sddfdhgdf]

I don't know if I agree with the proposition that the SO4 flows from right to left. As it is disposited knowhere, the inital status of equal density left and right is never changed. It seems more logical that the positive zinc and copper ions flow from left to right to equalize densities (assuming for simplicity that the initial solution consists of Cu++, Zi++ and SO4--)

[128j128]

Awesome vid.

"Not only is that stupid, it's very dangerous. Let's do it"

[FHomeBrew]

I watched this vid for the last 6 minutes about the kelvin thunderstorm thing. When does he say what you cited? Sounds interesting lol

[CaspaB]

I made one for my son in year 10 about 20 years ago. His teacher pulled it apart to find the electronics.

[Glendale1901]

He should've left the wrench on the car battery hehehe.