8.02x - Lect 10 - Batteries, Power, Kirchhoff's Rules, Circuits, Kelvin Water Dropper

[@lecturesbywalterlewin.they9259]

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!

[@PrakashKumar-nl3sx]

Lectures by Walter Lewin. They will make you ♥ Physics.

[@PrakashKumar-nl3sx]

sir today I am going to take admission in physics course because I love physics and your teaching methods also aids to my love for physics

[@walterwilliams6357]

Thank you!

[@raphaelpardes3519]

Lectures by Walter Lewin. They will make you ♥ Physics. y

[@narasimha4660]

Dear sir, you have made to love physics. You are the best teacher of physics.

[@toothless8965]

Those trying to study physics now don't know what they are missing out on. These lectures are so good!!!!! Best physics teacher ive ever seen.

[@ElectromecanicaIndustrial]

I remember when I first saw this lecture in 2013, the Kelvin water dropper was so amazing that I couldn't believe what my eyes were seeing. im rewatching all 8.02 in 2020, thank you professor

[@justinsantos5751]

Can you explain what's happening there?

[@anandapatmanabhansu]

Thankyou so much sir♥🇮🇳

[@ramjanreborn4212]

@@justinsantos5751 A good explanation is given by Vertasium on yt

[@martincardenas9459]

I majored in Control Engineering at the Technical University Dresden and I am now 77, but.it is really a pleasure to watch these lectures. Prof. Levin ist really an amazing pedagogue.

[@kevinwilliams5265]

Kirchhoff's Laws: 33:00

[@smylegalaxy2810]

Thank you bro

[@abozidabozid6162]

really thanks bro

[@stepbystepscience]

Excellent explanation, thank you for making these available.

[@topudas9970]

Because of you sir..I feel the love for physics.. Whenever i saw your class it gives me the strength to learn something new that i never found in my early life..You are the boss❤❤❤❤

[@bill-2018]

I've seen a few of these lectures now and they are all very good. I liked physics at school but the lessons were never this good. It all ties in with my hobby of amateur radio. I saw the lecture about capacitors and remember when I was aged about 11 taking apart a valve radio and stripping a capacitor and wondering what all the parts inside that radio did. At 13 I built a one valve radio from a kit. I found out more when I studied for the radio exam and learnt even more by building radios, valve at first, then transistors and finally built my transceiver with i.c.'s and FET's and MOSFET'S.

[@EternalPhoenix]

My physics teacher repeatedly assigns your videos to watch, and they are both very engaging and help me to understand the topic we are learning a lot. I know you seeing this is probably unlikely as this is an 8 year old video, but I just wanted to say thank you!

[@dxdx666]

It is so nice you have uploaded all these wonderful lectures on youtube ! I recommended them to my nephew who wants to study physics. Best wishes

[@francescocuccu4218]

Definitely one of the best teachers I've ever seen. Thank you very much :)

[@lecturesbywalterlewin.they9259]

Glad you think so!

[@vinodkhanna8470]

Namaste Lewin sir, this is Ritvik Khanna from India. Sir I am great fan of your explanation of physics and in future I want to become a teacher like you. 🙏🙏

[@prithwirajbhowmick4776]

Those who don't even know the basics of physics are enjoying his lectures!! This defines how well he teaches!!😊😊

[@kristifrroku3170]

The best professor ever...Just brilliant!...Truly coherent in connecting concepts

[@PrakharPaawanSaxenaInqalab]

before two months I hate physics. Now after watching you i am loving it. Also there is a leap in my physics marking. Thank you very much sir....

[@lecturesbywalterlewin.they9259]

great! 😊

[@parthkatke6706]

48:46 Sir, why it is so that the water is spreading only in can B and it is normal in can A? Or is it just we can't see it spreading in video?

[@TheGREDATV]

another perspective of the mesh analysis, now with the physics that work underneath, thank you doctor

[@VickysTuition]

@30:50 why doesn't the professor get electrocuted here? There is a huge current going through the tool and he is touching it right ? Won't a part of the current go to the ground ? Or does that work only with static charges ? Since this is a battery.. like galvanic cells, the zinc's electrons in the anode are attracted only to the Copper ions of the cathode and not to the ground ?

[@patrickario5259]

Am a graduate in physics from Uganda I love the way you explain physics. And it assisting me so much because am a teacher in high school

[@khandkertiashazad6858]

At 8:13 you cover the resister drawn in the circuit with your hand and say, "if the R is not there, that means the resistance is infinitly large". Shouldn't the resistance be zero?

[@lecturesbywalterlewin.they9259]

what I meant is: If you remove R and do not reconnect the wires, the resistance is infinity.

[@ussecurity3997]

I had the same doubt... thanks

[@rgudduu]

means if resistance is physically not present where it is now. Meaning it becomes open circuit at that location

[@justgivemethetruth]

I love the Lord Kelvin's Thunderstorm experiment/demonstration. It seems like the most amazing thing. One thing I wonder is if the charge polarity always establishes itself in the same direction, or does it vary randomly by 50%? If it is the same or does not vary equally, what might account for that. The lectures are amazing. Another one I really like is the one of light and color ... mindblowers. What a universe.

[@lecturesbywalterlewin.they9259]

:)

[@buggsy5]

It establishes randomly, depending on any slight difference in initial small charge differences on the rings and buckets. There will always be some slightly different charge difference - due to such things as slight differences is the electrostatic charge gradient in the air or someone walking close to the apparatus.

[@justinsantos5751]

I always see the guy at 31:22 sleeping in every lecture lol

[@gauravsidar1885]

🤣🤣

[@amisharawal3967]

I just don't understand how someone can sleep during such an interesting lecture......

[@Torchl146]

@@amisharawal3967 noobs are everywhere even outside virtual life

[@saksham8412]

@@Torchl146 he is taking notes and not sleeping

[@namratakadam8007]

The lectures are awesome sir, this teaching is captivating.

[@selliahelango6899]

Long live sir ❤️ Made physics something lovable forever....

[@thx1138y]

Hermosos ejemplos y gran dedicación por la enseñanza.Un abrazo y muchas gracias por la Lec.Las estoy viendo una a una en mi cell phone...I learned a lot. TKS!!!

[@lecturesbywalterlewin.they9259]

+thx1138y muchas gracias

[@JaiPrakash-bk3uv]

sir I love you more than physics sir. you are really great person

[@lecturesbywalterlewin.they9259]

:)

[@architmittal668]

I am preparing for JEE and your videos really help.

[@aassimhussain2807]

hope you cracked it.I am preparing for the 2024 jee

[@Shri100percent]

wait why does he say at 40:00 that the potential goes down in that direction? was it something i missed before?

[@crookshanksacademy]

If charges move in the direction of electric field, then potential decreases. If charges move against the electric field, potential increases. Hope it helps ✌

[@MrSomethingdark]

Guy knows the power of love.

[@shahbazalisangrasi8576]

After watching these videos, I am really getting in LOVE with PHYSICS..... Thanks a lot Sir

[@lecturesbywalterlewin.they9259]

:)

[@Warpedsmac]

What I would have given to sit in that lecture theatre.....Thanks for posting this to YTube Professor Lewin!!!!

[@sushiljangir956]

Sir your are the best physics lecturer. Superb sir.

[@lecturesbywalterlewin.they9259]

So nice of you

[@sudarshanhs6588]

At 27:36 , it is mentioned that as the temperature of the battery increases, it would increase the internal resistance of the battery. This would be the case if its a normal resistors, but in batteries internal resistance is due to electrolyte resistance and its know to go down as temperature increases as higher temperature promotes chemical reaction at accelerated phase. This is infact why shorting big batteries is a dangerous thing. It can lead to thermal run away

[@lecturesbywalterlewin.they9259]

Battery's are a chemical reaction. All chemical reactions speed up when heated. So the voltage degradation/leakage internal to a battery should speed up with temperature. If you get so hot that the seals in the battery break down then you have immediate failure. Unfortunately the seals in the battery don’t like cold much either so taking a battery too cold could compromise the seals too.

[@sudarshanhs6588]

@@lecturesbywalterlewin.they9259 Thankyou for the quick reply, I just wanted to point out that if anything, the battery would discharge more once it starts heating up as its internal resistance goes down at Higher temperatures

[@usmanmuneer6143]

I really like your voice from the secondary camera mic.

[@BarriosGroupie]

A great example of how teaching standards can range from the _outstanding_ such as here with Prof Walter Lewin to 'barely acceptable' where the lecturer reads from a book.

[@nagmahasan9966]

You and your team is fabulous .

[@rinzej]

4:45 I could be wrong, but I´m afraid I don´t see an E-field across the membrane pointing from the right to the left. Between the Cu-electrode and the solution there will be a + potential difference and between the Zn-electrode and the solution a - potential (the standard potentials of Cu and Zn) As a result of this you get at the right side an extra negative charge (SO4- ions) in the solution and at the left side an extra positive charge (Zn+ ions) in the solution. SO4- ions will then flow from the right side to the left side... I think the E-field is present just around the Cu-electrode, pointing from it, and around the Zn-electrode, pointing to it. But great lectures, thank you for uploading them!

[@lecturesbywalterlewin.they9259]

Rinze Joustra There is no membrane. Watch my lecture and my explanation again please.

[@h7opolo]

3:45 wouldn't the current be flowing from negative terminal through the circuit to the positive terminal? 7:48 same thing here. i understand you might be talking about "conventional current", but i am reversing the arrows in my notes.

[@lecturesbywalterlewin.they9259]

the direction of current is uniquely defined. watch my 8.02 lectues.

[@h7opolo]

@@lecturesbywalterlewin.they9259 yes, at the beginning of the prior lecture, lect 9, and also in the intro to the course. Ok. thanks. I will expect electron flow then to be explicitly stated and opposite the direction of any mention of "current."

[@harshsoni9029]

I have a doubt that.. how the resistance become Infinite when we remove the resistance R from the circuit 🙄.. 8:39

[@ilakkiyanilakkiyan3063]

Because, there is no current if the resistor removed(Circuit incomplete). If there is no current, then we can take that has infinite resistance

[@sebbyteh9203]

it is also very dangerous, so let's do it, WALTER LEWIN STYLE !

[@lecturesbywalterlewin.they9259]

ha ha ha

[@AdityaKumar-ij5ok]

Lectures by Walter Lewin. They will make you ♥ Physics. can you please answer my question just posted recently in the comments?

[@ajaykumarchavan8472]

@@lecturesbywalterlewin.they9259 sir assignment is not opening were can I get assignment

[@niporessas]

I have a question about the explanation between 0:50 and 6:57. Does it mean that batteries prevent the issue where the current direction opposes the field direction?

[@lecturesbywalterlewin.they9259]

it will take me too much time to watch most of that lecture again - sorry

[@niporessas]

@lecturesbywalterlewin.they9259 That's fine, my question is whether the battery resolves the issue where there is a part of the circuit where the direction of the current opposes the electric field. Specifically, I would like to know if the battery prevents this from happening in direct current (DC) circuits. Or if this still keeps happening even with the battery

[@maximocaceres4685]

Potato experiment was fun. Thanks, professor! Amazing lecture as well.

[@brod515]

@8:12 why is it that when the resistor is taken out there is infinite resistance shouldn't there be no resistance. the resistors job is to resist and its not there

[@aravindhsm1287]

Resistor being taken out means the circuit is no more complete,which implies that no current passes through the it. An infinite resistor also does not allow any current to pass through it. So,we can think of a broken circuit as one with an infinite resisitnace.

[@khandkertiashazad6858]

Professor, like at 38:45, what if i1 and i2 both flow through the same battery instead of a resistor? Should we ignore the current flowing in towards us from the other loop in that case?

[@lecturesbywalterlewin.they9259]

follow the recipe that I discuss in this lecture and you will have your answer.

[@munguis]

At 8:10, what do you mean by R=infinity? Do you mean that if we remove the resistance ,we have an open circuit? Because if we simply get rid of the resistance and leave a closed circuit, then the resistance would not be infinity for the charge can flow freely.

[@lecturesbywalterlewin.they9259]

>>>Do you mean that if we remove the resistance ,we have an open circuit?>>> yes

[@waihan6772]

Hello professor, When you short-circuit the car battery, you did it with bare hands. I'm wondering why it's not dangerous, assuming that the current is about 600A in the wrench. Isn't it possible that the current could flow through your body?

[@anshsoni1625]

Current follows the path with highest potential difference The current chooses to go through the -ve potential terminal of the battery rather than the earth (through his hand) which has potential of 0 as the potential diff from positive terminal to negative is higher than that of earth

[@mohamedabohegy3938]

in 10:30 i can't understand how the potential difference will be zero when we shorten the circuit but at the same time there is flow of current. in other wards what will make current flowing unless there is no potential difference (delta V=0)

[@vanshsehrawat8997]

I found someone who will improve my English

[@obayev]

Thank you sir, your lectures are so great!

[@lecturesbywalterlewin.they9259]

Most welcome!

[@ankitsoni9275]

27:00 in india we used to shoot 9v battery 🔋 by our 😛 tongue .......🥰🥰🥰🥰

[@XxPlayMakerxX131]

48:00 Getting that high education for free

[@muhammadsiddiqui2244]

Thanks to the great Prof. Lewin Walter

[@surendrakverma555]

Very good lecture Sir. Thanks and Regards 🙏🙏🙏🙏🙏🙏🙏🙏

[@WCM1945]

Costructive criticism: You illustrated what I call _hole flow_ earlier, but have switched to the _electron flow_ convention at about 32 minutes. Granted, you point out that it makes no difference in the laws or the math, but it might be preferable not to switch back and forth like that. for your lectures. I'm speaking as a former electronics instructor, where _electron flow_ was the standard.

[@Abhisheksharma-lk4ll]

Merry Christmas dear professor, may you live Long and happily , with love from-Abhishek sharma.:) Love you

[@apitipapa6183]

I couldnt understand that why didnt he get shock while putting wrench on batteries? can anyone explain it to me :) Thanks from TUrkey

[@prajjwal9366]

You said when you remove resistance 'R' Resistance become infinite so zero current flowing? But how please make me understand 🙏 My second question In battery current flow from + to - terminal! If it does not go through the battery then what is the need of internal resistance? Maybe I am not able to understand mechanism of battery! Please explain me with satisfying example! Please reply me 🙏🙏

[@lecturesbywalterlewin.they9259]

plse don't be lazy, I cover all this in my 8.02 lectures. When there is no R between the poles of a 9 V battery there is no current, but the potential difference between the poles is 9V.

[@ankisbegummina8941]

Dear professor, you said at 3:06 that there is a potential difference between solid Zn and Cu. So what would happen if we connected them with a wire without any dipping them in any solution? Will current actually flow?And if so, for how long and why would the current stop flowing at some point?

[@lecturesbywalterlewin.they9259]

no current will flow

[@J.RRandallIllinois]

professor Lewin, what variables are involved in increasing the voltage ? If you raised the height that the water falls, add a chelated iron to the water ,use a copper bucket instead of steel , just throwing ideas out there. If you put a voltmeter in the 2 buckets would you be able to read a d.c voltage? thank you for taking the time, appreciate you're lectures.

[@peeper2070]

48:45 The split second pause before 1% of the audience understood 😂

[@koma2000music]

47:53 aah... I wasn't looking. Thanks Prof Lewin for your amazing lecture series, and for keeping the viewer's attention at all times!!

[@lecturesbywalterlewin.they9259]

you are welcome

[@sebastianrada4107]

Why did the professor didn't suffer any damage when shorting out the big battery? Isn't it logic that the current would use him a resistance?

[@rgudduu]

At around 34:30 u said "We can take any loop, even in space around the circuit, and still integration E.dl=0 is valid." What if I take a loop including the middle resistor (R3) in the circuit, but the rest of the loop is in space around the circuit. Means E.dl along the middle resistor bet its two terminals, has to equal the E.dl in a path in space bet those terminals. I don't understand how. What is the E in space around the circuit?

[@gruppoid]

Yes, E.dl along this loop is zero. Which means e.g. that there is a voltage between a terminal and a point in space outside the circuit. However there is obviously no current flowing between these 2 points, it only flows in a conductor.

[@pkillor]

Dear Professor, What will happen, if the Kelvin Water Dropper experiment, were to be performed at higher atmospheric pressure? Thank's!!

[@sandeeppatidar1106]

Best teaching.Thank you professor

[@lecturesbywalterlewin.they9259]

Glad you think so!

[@JaiPrakash-bk3uv]

love from india. may you live long sir.

[@lecturesbywalterlewin.they9259]

I have 5+/-5 yr to go. That will be IT!

[@yograjbir9993]

@@lecturesbywalterlewin.they9259 sir iits you will stat your new journey in another realm of existance. so be positive...

[@Espectador666]

@@lecturesbywalterlewin.they9259 You are still going strong at this point and your legacy is legendary

[@GaganpreetSingh-ft1xi]

If I attach a pure inductor to an AC source then is it true that the The induced EMF in the inductor is exactly equal and opposite to the emf of the source irrespective of L of the inductor? If not why. And how can we apply Kirchoff law if it is not true?

[@lecturesbywalterlewin.they9259]

*KVL can never be used in the case of an induced EMF* watch my lectures.

[@GaganpreetSingh-ft1xi]

@@lecturesbywalterlewin.they9259 oh sorry sorry, i want to say Faraday's law. Please explain how we can apply Faraday's law.

[@lecturesbywalterlewin.they9259]

watch my 8.02 lectures where I cover RLC and RL circuits.

[@shengwencheng8040]

Hi, professor: I find that almost every courses I took introduced the Kirchhoff's Rules in another form which are called KVL and KCL. I had a hard time to digest them in my head. The one you explained (Integral of E.dl = 0) is much easier for me to understand the idea behind those equations. Wikipedia also only introduce in the form of KVL and KCL, so I think maybe Wikipedia is not a right place to learn science properly.

[@lecturesbywalterlewin.they9259]

:)

[@dangthanhnghia4720]

When you mention in 10:31, the Vb goes to 0, so is it possible that we still have the current? I don't understand why we still have current when the difference of electric potential is 0. Can you please explain to me? And, suppose I connect a 9v battery's + with a conducting wire, and connect that wire to this battery's -, what will happen?

[@dangthanhnghia4720]

Also, why are you still ok even though you touch the screw connected to the car battery (in 30:26)

[@lecturesbywalterlewin.they9259]

To touch a 12 V battery is without any danger,

[@lecturesbywalterlewin.they9259]

I watched from 9:30-11:30. I cannot improve on the clarity of my lecture. I suggest you watch it again. If you short out a 9 V battery with a copper wire, the current will be limited by the internal resistance of the battery. I don't expect any "firework". I expect that the battery will be dead within 5-10 minutes.

[@dangthanhnghia4720]

+Lectures by Walter Lewin. They will make you ♥ Physics. I'm sorry, what's the next part of the explanation. And, is it ok if I charge my phone ( or any electric devices), and leave it charging even though it's full charge?

[@lecturesbywalterlewin.they9259]

I explain the Kelvin water dropper in a later lecture. >>>>.And, is it ok if I charge my phone ( or any electric devices), and leave it charging even though it's full charge?>>> Read about this on the web.

[@HarshYadav-ot9xu]

The different resistance attached in fan it and its help is to vary the speed of the fan as the current flows the rate of consumption of the power will be same if we run it at different resistance? Or will be same

[@mohammadbinmahbub9160]

why does the current go in the opposite direction to E within the cell? i.e. got from +ve to -ve as current does

[@lecturesbywalterlewin.they9259]

*chemical energy* is the reason

[@parthkatke6706]

@@lecturesbywalterlewin.they9259 Professor, I want to know the name of the course book name and edition to complete the assignments. Please tell

[@lecturesbywalterlewin.they9259]

@@parthkatke6706 8.02 Physics for Scientists & Engineers by Douglas C. Giancoli. Prentice Hall Third Edition ISBN 0-13-021517-18 all asignments and exams are posted as PDF files below the video thumb nails

[@lollolzi2996]

8:15 if that '' R '' is not there then shouldn't there be infinity current running through since there is nothing resisting the flow of the current? I=V/R

[@lecturesbywalterlewin.they9259]

all power sources have an internal resistance.

[@MaherKaderDrums]

If the internal resistance of the power supply is r_i, then why does R = infinity, and not r_i in a situation where you remove the external resistor? At 10:04 , you mention "if I short out the battery" - isn't that what the example at 8:14 is doing? Removing the external resistor essentially connects the two terminals of the power supply together.

[@lecturesbywalterlewin.they9259]

question unclear.

[@amj.composer]

Genuine laugh at 23:54 Love you and your videos Professor Lewin!

[@pranjaljain6762]

@12:50 what would happen if you arrange battries with negligible internal resistance in parallel what would be emf in circuit then?

[@lecturesbywalterlewin.they9259]

question unclear

[@pranjaljain6762]

Lectures by Walter Lewin. They will make you ♥ Physics. We put batteries in a configuration like parallel resistors in a circuit. then what would be the emf

[@lecturesbywalterlewin.they9259]

at 12:50 I show you what the emf is that is produced by my Cu Zn battery.

[@trale1872]

Cu should not be reacting to h2so4 yet there is Cu2+ in the solution? I'm confused. And also what chemical reaction SO4 2- participated in for them to go against the current flow?

[@namanhtu4938]

Professor, What did you mean when you divided two terms by dt and said "you shouldn't tell your math teachers"? What is mathematically wrong with that?

[@jayshreegohil2716]

U divided a equation nearly by 0

[@gruppoid]

dW/dt is a derivative, not a division. We pretend that we find the derivative by just dividing these "infinitely small" numbers.

[@gruppoid]

en.wikipedia.org/wiki/Leibniz%27s_notation

[@tomieemile]

@@jayshreegohil2716 That's not a problem, nearly 0 /= 0

[@GaganpreetSingh-ft1xi]

Sir there is another question : If i attach a pure inductor to an AC source . Then is it true that induced emf is always equal and opposite to the emf the source , irrespective of the L of the inductor. If NOT then how can we apply Faraday's law to this circuit. Please explain 🙏🙏🙏🙏🙏🙏🙏

[@GaganpreetSingh-ft1xi]

Sir this question

[@tomieemile]

@@GaganpreetSingh-ft1xi He's not your personal google search engine buddy

[@divyadharshinim1042]

Amazing lecture sir.I have a small doubt.why circuit without resistor has infinitely high resistence?? Can anyone help me in this?please

[@samuelbency8104]

I think what he meant there was that the resistor wasn't there and instead it was just air (the circuit wires weren't connected when the resistor was removed, the wires were simply left like that). So the resistance instead becomes that of air(around 1.5 x 10^16) which is really high. I hope that it helped

[@divyadharshinim1042]

@@samuelbency8104 Thank u.That helped 😀

[@CaptainCalculus]

Where does the H from the H2SO4 go? Just checked, the Cu becomes sacrificial and ZnSO4 and the H2 is dispersed--Zinc sulphate being carried out by H2 molecules would smell disgusting, like a rotten egg factory

[@lecturesbywalterlewin.they9259]

:)

[@Ashusingh-ze5jp]

Pls help me power loss in transmission by Walter Lewin which lectures

[@trale1872]

Cu should not be reacting to h2so4 yet there is Cu2+ in the solution? I'm confused. And also what chemical reaction SO4 2- participated in for them to go against the current flow?

[@JaiPrakash-bk3uv]

sir I am confused that emf of a battery = IR or potential difference between two terminal of battery =IR

[@holipinieo1]

emf=i(r+R), 'r' is the internal resistance of the battery and 'R' is the resistor attached in circuit to the battery. V=emf-ir

[@Abhisheksharma-lk4ll]

Sir at 10:35 you said that " it doesn't mean there is no current running, but it means between point A and B , the potential difference goes down to zero" . sir but if there is no p.d between points A and B than how can there be current ? :)

[@lecturesbywalterlewin.they9259]

I watched at 10:35. What I have is perfect. I cannot add to the clarity - watch it again. If R=0 you have a circuit with an EMF (the battery). I=EMF/r, here r is the internal resistance of the battery

[@lecturesbywalterlewin.they9259]

If you attach a voltmeter to the poles of the battery with R=0 the voltmeter will read ZERO but the current through the circuit will be I=EMF/r

[@mrbigvolume6066]

Your method for solving kirchoffs current law is how we were taught at U of akron. when you have a 3x3 equation you really need to watch your signs. We called this mesh analysis.

[@hridayamkrishnahore2964]

Sir If a battery reads 1.5 volts then how what do we mean by that as per the classical definition of electric potential

[@lecturesbywalterlewin.they9259]

it means that as long as the battery draws no current that the potential difference between its 2 sides is 1.5 V.

[@hridayamkrishnahore2964]

@@lecturesbywalterlewin.they9259 if I want to express this potential difference in a way that I bring a test charge from infinity to a particular point then how do I say it

[@lecturesbywalterlewin.they9259]

@@hridayamkrishnahore2964 The electric PE in Joues or in eV of one pole depends on its environment. It could +or - hundreds of Jules it could also be zero if you attach that pole to the ground.

[@maxt774]

At 8:10, how come if the resistor is not there, R=infinity instead of R=0 because there is no resistor?

[@maxt774]

Ohhh, I think I just realized what you meant. When you said the resistor is not there, did you mean that there is now a break in the circuit so that's why R=infinity? In my head I just was imagining that with no resistor there was just one long continuous wire that went around the batter similar to the case where you short out the load.

[@mahmouddesokey3818]

Sir , at 30:51 , why didnot you get an electric shock ? Is it because your resistance is much higher than the wrench ?

[@lecturesbywalterlewin.they9259]

when you touch a car battery you do not get a shock.

[@mahmouddesokey3818]

@@lecturesbywalterlewin.they9259 But you are touching the wrench which represents a path for current .

[@Jim89M]

@@mahmouddesokey3818 He doesn't touches both terminals of the battery, but even if he did the 12Volts of the battery and the high resistance of the skin are not enough to allow a high current to pass through him and shock him.

[@bhanu8391]

30:48 , sir, why did not you get a shock when you shorted car battery of large current?

[@lecturesbywalterlewin.they9259]

no current went through me.

[@bhanu8391]

@@lecturesbywalterlewin.they9259 could you explain me sir, though you held the rod with bare palms why no charges passed through you? Was you insulated yourself by any means or just your shoes were strong enough? Thanks sir for reply, 😊

[@Jim89M]

@@bhanu8391 because the other terminal in this case is not the floor like the Vandegraaf experiments he did on other lectures. The current will flow between the two poles of the battery through the wrench, not between one pole and the floor through the professor. But even in the case you put your hand between the two poles, according to ohm's law, the 12 volts of the battery and the high resistance (much higher than the steel of the wrench) of your skin are too low to allow a high enough current to pass, so not high enough current passes to feel or harm you.

[@ivansmirnov362]

@@lecturesbywalterlewin.they9259 Sir, i got a little bit confused: does voltage depend on resistance? I always thought (since the electric field is conservative) potential energy depends only on initial and final positions. Thank you.

[@JaiPrakash-bk3uv]

sir in 1:00 the shape electric field lines from +ve terminal of cell to -ve terminal of cell is not smooth. in the corner of circuit it is not smooth. electric field lines are taking turn. but we know electric field lines are smooth

[@lecturesbywalterlewin.they9259]

connect a copper wire over a battery. put knots in the wire make sharp turns. The E-field will always be in the wire.

[@Abhisheksharma-lk4ll]

Sir at 8:18 you said that "if that R is not there that means the resistance is infinitely large" but sir if that R is not there so resistance will be only that of wire which is negligible approx zero, so how you said R= INFINITE? :)

[@lecturesbywalterlewin.they9259]

currents through an open circuit are in general near zero. It all depends.

[@lofijedi]

anyone here cuz your school shut down due to corona virus?

[@keyss78]

I wish we had this resource when I was in school/college, he makes the concepts so easy to understand...

[@kinglogic1729]

Yeah I'm a rising junior and am bored (and also preparing for taking AP Physics).

[@uncocoloco6862]

Yeah because our physics teacher doesn't care :D

[@dipayandasgupta7506]

@@kinglogic1729 nice even im in grade 9 doing 11th and 12th grade physics. Im from india though. Are you preparing for international physics olympiad by any chance?

[@navirashandra9567]

Professor, you said that so4 ions go from the right to the left and they travel through an electric field that opposes them, but why on the picture you drew, the E field arrow pointing left which means it goes from right to the left too ?

[@lecturesbywalterlewin.they9259]

how many minutes into the lecture?

[@Graham_Wideman]

The electric field arrow is drawn in the direction that it would move a positive charge. But the so4 ions are negative, so the electric field pushes the so4 ions in the direction opposite to the arrow.

[@BumbleTheBard]

Unfortunately, in the early part of the lecture, Prof Lewin flits back and forward between describing two different galvanic cells. If you put a zinc electrode and a copper electrode into sulfuric acid, there are no copper ions involved, and there is no need for a membrane to separate the electrodes. The overall electrochemical reaction is zinc plus hydrogen ions going to zinc ions plus hydrogen (gas). The Daniel cell is quite distinct. In that cell, you have a zinc electrode in zinc sulfate solution, and a copper electrode in copper sulfate solution, and a salt bridge between the two to keep them separate. There, the overall reaction is zinc plus copper ions going to zinc ions plus copper.

[@kailuigi3793]

Why is the closed loop integral of E dot dL in a closed circuit equal to 0? isn't that a special case for when we have conservative fields when there are no charges moving and yet in our circuit charges flow from one side to the other all the time

[@lecturesbywalterlewin.they9259]

closed loop integral of E dot d is ONLY zero if dphi/dt = 0 That's called Kirchhoff's loop rule.

[@18141776hhhh]

That’s not just spark, You can’t make lightning from a “wet blanket?” Some buckets and pails yes! Dripping water, The clean scent of negative ions after a rain for how long has the potential been overlooked? If you left the water running the model would continue to spark

[@pravshah8265]

What is shorting of the battery, if we connect a wire to battery terminals, without any resistor does it mean we are shorting the battery. What happens when we short something? When the two charged planes connected to a battery when we bring extremely close till they touch each other do we get a discharge and what effect does it have on a battery?

[@lecturesbywalterlewin.they9259]

shorting is VERY bad for the battery - it overheats and can even explode. ask Goggle also for details.

[@babitachaubey491]

Why current is not reduced by the resistors in kirchoff closed loop. It's ok that number of charge entering the resistor equals number of charge leaving but current= quantity of charge flowing/time. Current= number of charge [in coulombs] leaving resistor in "one second"(current 1) should not be equal to number charge entering in a resistor in "one second"(current). As resistors reduce energy of charge so charges with low energy will take more time to flow(charges leaving resistor per second should be low that is current leaving resistor should be lower than the current entered the resistor with higher velocity) as their energy is reduced hence current should be reduced however total number of charge entering resistor and leaving it will the same irrespective of time taken Please answer🙏

[@Jhonatan31415]

Sorry for any mistakes in the grammar, as english isn't my first language. Thanks for all the content and love for physics you pass for all the students, all students I recommended your lectures loved and said that it was the best lectures of physics they have ever watched. Now my question, in moment @39:22 when you say +I2R3 you say that the potencial on the "bottom" side must be greater than the top side of the resistor, shouldn't be the inverse of that? Because if you have an increase in potencial the bottom side must be at a lower potential than the top side, I guess. And again, thanks for all the content and love for physics.

[@lecturesbywalterlewin.they9259]

what I have is correct. I1 and I2 are in opposite direction. If you go from the top to the bottom of R3, you go in the direction of I1, but you go against I2. Thus using my convention going through R3 we get -I1*R3 + I2*R3.

[@Jhonatan31415]

Yes, the sign was correct, my doubt actually was in what you said, in I1, we go through R3 from a higher potential to a lower potential, but I2 goes in the opposite direction, from a lower potential to a higher potencial, thus the positive sign. But you said that I2 goes from a higher potencial to a lower potencial, this would make -I2R3 using your convention, and from my perspective it's the inverse, that was what confused me.

[@lecturesbywalterlewin.they9259]

I can see that you were confused. I should have use different words. Going form the top to the bottom of R3 we go in the direction of I1 but against I2. I should have left ti with that.

[@Jhonatan31415]

Thanks for the explanation.

[@bill-2018]

When I was about 10 I had a book: Batteries, Bulbs and Magnets with experiments in. One was using copper sulphate crystals and a battery to copper plate things, my eldest sister got me the copper sulphate. Another I recall was to wrap wire round a nail to make an electromagnet. I put a 9 Volt battery on a transformer and got a shock. I couldn't understand why. I found out why later and it's why I put reverse biased diodes across relays when I make things.

[@hussain7md166]

Amazing lectures

[@babitachaubey491]

Walter Lewin sir, it has been three days since i asked the question regarding current in the comment section. Please answer it. I'm so much confused how in kirchoff's current law, the current moving with energy of mv²/2 leaves conductor with same current with which charges entered the resistor. The mass in mv²/2 cannot be reduced so for the voltage drop the kinetic energy reduced is due to reduction in velocity of electron. So why do we say that in a closed loop the current leaving resistor is same as the current which entered the resistor. I think the charge entering and leaving resistor is same and not the current as current is quantity of charge flow in one second(I=q/t) and since velocity is reduced less number of charges will be leaving resistor in *one second*

[@thx1138y]

Sr. im from chile..im afraid that high voltaje water source works by charge of the electron on movement (water) thats chargue the cans?..tks..!!!

[@karbonnphone6340]

in our homes if we keep the plug switch on without connecting any appliance, is there any power consumption

[@lecturesbywalterlewin.they9259]

Many electronics(such as TV and Computers) when switched off consume power. There was an interesting article in the New York Times about this about 2 months ago. The ONLY way to prevent that is to unplug them.

[@karbonnphone6340]

Lectures by Walter Lewin. They will make you ♥ Physics. thanks sir what would happen if we don't connect anything ( no comp or tv but judt the switch of the mains on)to the mains but just keep the switch on, is there still any consumption?