8.02x - Lect 5 - E= - grad V, Conductors, Electrostatic Shielding (Faraday Cage)

E = -grad V, More on Equipotential Surfaces, Conductors, Electrostatic Shielding (Faraday Cage), Great Demos
Assignments Lecture 1, 2, 3, 4 and 5: freepdfhosting.com/2cb4aad955.pdf
Solutions Lecture 1, 2, 3, 4 and 5: freepdfhosting.com/75b96693f2.pdf

[@mukeshsuman9306]

thank you sir , i lost interest in physics due to my teacher ( i am in india ) , but suddenly you tube recommended me your videos 94 mit lectures , and now i have to say i have fallen n love with physics , I LOVE YOU SIR !! 😇😇😇😇

[@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!

[@fdaalderop5057]

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

[@amanrubey]

Lectures by Walter Lewin. They will make you ♥ Physics. which website?

[@user-mf2sc8xu6v]

Thank You.... Sir.... Thanks for Your Guidance... It's pleasure to learn physics from you...!!! 🌠💖🌠💖🌠💖🌠

[@willtheelectrician8184]

Lectures by Walter Lewin. They will make you ♥ Physics. New subscriber here working my way through your lectures. This is awesome! I would love to hear a conversation between yourself and Wallace Thornhill. Thank you professor. The world appreciates your free giving of information.

[@cmetube]

Glad you're still teaching Physics, Professor Lewin. You taught me everything I know back in the 80's! Thanks!! ❤️

[@BentHestad]

These lectures are amazing! I consider them a gift to humanity, no less. Thanks again, Sir!

[@lecturesbywalterlewin.they9259]

:)

[@TheOneMastodon]

Professor Lewin, that lecture was shocking, electrifying and simply *wicked cool* !

[@lecturesbywalterlewin.they9259]

:)

[@balajimali1292]

@@lecturesbywalterlewin.they9259 Best on youtube👍👍👍

[@of8155]

😁

[@sourya81487]

In the last what happened.... I didn't get it.

[@oximas-oe9vf]

@@sourya81487 He charged the cage up,but since it's a closed Surface the charges rearange only on the outside (Non on the inside) therefore he didn't get zapped

[@Balaji-uz8kp]

21:39 WOW! Thousands of video lectures on KZbin but I decided to watch this one on Valentine's day. What are the odds of that? BTW, thank you professor for uploading your lectures online. Awesome stuff.

[@TheDatolo97]

After reading your comment, I noticed that this video was uploaded the day before Valentine's day

[@herzikkimolog]

whoosh I just watched it at 13th Feb as well.

[@GianlucaUK]

Well, at the moment I'm writing, this video has been up for 5 years and a half, which I will round up to 2000 days, of which 6 were Valentine's day. There are 222,111 views. I appreciate they may not be evenly distributed, but an average calculation tells me that more than 600 people must have watched this video on Valentine's day. I see two comments remarking that. 2 out of 600 doesn't seem like a lot after all. So, what are the odds? For you, it is roughly 1/365. For everybody else, it is an extremely likely event to be reading your comment.

[@imnimbusy2885]

16th Feb but close enough

[@nikelaosh]

i'm watching it on february 13th....

[@milirojas4640]

its so nice to be able to take your lectures despite being thousands of miles away from your classroom, they really have changed my vision of physics, thanks a lot!!

[@abishekbalaji7716]

what a taste you've got for humour! makes learning all the more fun

[@lecturesbywalterlewin.they9259]

:)

[@ashutoshnamdeo602]

You're the most amazing and best phy magician and you really made me fall in love with physics ♥️ thnku Walter Lewin sir

[@lecturesbywalterlewin.they9259]

It's my pleasure

[@mpzelectromechanical1320]

49:11 “Since I’ve taken 8.02, I’m not afraid.” Thank you, Sir.

[@felixov8285]

THANK YOU SIR, I AM AN ENGINEERING STUDENT IN SPAIN AND SINCE I FOUND YOU I DON'T HAVE TO MEMORIZE ANY EQUATIONS, CONGRATULATIONS

[@studywithjosh5109]

After taking multi variable calculus last summer, this lecture paired with the last have to be my favorites so far. The insight into grad makes me me complete!

[@SunSpotOnne]

These lectures are done so much better than my first year physics lectures. They also seem more challenging, (integrating vectors looks scary).. My school has a very poor physics department. Thank you for the lectures!!

[@risharodrigues6525]

Thank you so much for uploading your lectures Prof.Lewin...Im really beginning to love physics.

[@andrejburcev6023]

Haha, just resumed the video at 21:50 and first thing he says - “In honor of Valentine’s day...” and today is really the Valentine’s day 😃

[@lecturesbywalterlewin.they9259]

very cool

[@lavalampex]

I was prepared to hear some kind of in honor of a great man in history from the field of physics. :D

[@echadmiyodea]

*Carl Jung likes this

[@rishabhsinghrajpoot6002]

Me too accidently watching it on valentines day 2021

[@divyakumarjha5766]

I never thought this could also be an explanation for charge distribution on conductors U made my concept so crystal clear 😃 thank you so much sir 😄

[@ramandhingra3764]

This lecture is the best thing I've seen ever especially the experiment with the Faraday's cage. These experiments build the intuition one needs for studying physics. Really I am mesmerized after watching this. Thanks professor❤

[@intomd3730]

This course is amazing Sir. You really made me love physics.

[@lecturesbywalterlewin.they9259]

:)

[@SkyhawkSteve]

I took my undergrad physics class back in 1982 and enjoyed it quite a bit. Still, I'm going through these videos and loving it once again. Thanks very much! For what it's worth, I'm an electrical engineer and did some work with Electromagnetic Compatibility testing, where I did testing in a semi-anechoic chamber... which is really a very large (and expensive) Faraday cage that absorbs the radio frequency reflection inside the chamber. In that sort of work, it's quite important to remember all of the basic physics! Thanks again.

[@lecturesbywalterlewin.they9259]

:)

[@libertyurias7523]

YOU ARE SAVING MY PHYSICS GRADE. i love the way you teach the concepts

[@wobamoshitio2165]

Awesome lecture... I wished I too had a teacher like you sir. All I learn in my college days was nothing .... Wish I can meet you once before I die... Lots of love and respect Sir. From India, Nagaland

[@shreyamehta5800]

The best physics's creation is you sir :-)

[@brahimbenhammou4867]

One thousand Thanks to you Mr.Walter Lewin for sharing such beautiful courses with really make every scientific brain loves Physics and Science in General. All Respect and please continue innovating and sharing wiht us and we hope we can do so.

[@AdityarajXIC]

Hey professor !!! You are really amazing l am in class 12 and preparing for JEE 2021 and l missed the lecture of electrostatic shielding in the class .. But now l am not tensed ....because your lectures are really amazing 🙃🙃🙃🙃🙃🙃🙃

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No hard feelings... Just asking, how did the paper went?? This year, I'm in class 12th and have the same goal as yours... So, what can I expect???

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@@Quantramix even i want to know where these guys are now cz in 2024 i too will be appearing for my jee..and hopefully to IIT

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Awesome lectures given by an awesome teacher. Thank you for the excellence!

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Probability of me having a notably different career right now if I'd had these lectures circa 2004: .99. Thank you for the re-inspiration, professor!

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The master at work! So very enjoyable to watch.

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I would like to call your teaching as great innovation in ACADEMIA. Love from india❤

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sir nothing to say u are just of god-level ur lectures are just out of the world. love from India.

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Thank you so much! These lectures really make me love physics. It's becoming kind of addictive :)

[@lecturesbywalterlewin.they9259]

Happy to hear that!

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I wouldn't attend 50 mins class of school... But your lectures, but your lectures will be never missed..

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Professor Lewin, I love your lectures. :)

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Sir,your lectures are very informative and to the point,very comprehensive indeed

[@lecturesbywalterlewin.they9259]

:)

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[@lecturesbywalterlewin.they9259]

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I don't feel wasted if I watch one of his lectures every day.

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Thank You Sir! Cheers from Aerospace Engineering in Rome!

[@akashhera]

Thanks a lot sir,for making them available for anyone around the world! :)

[@lecturesbywalterlewin.they9259]

So nice of you

[@user-wq9wi8er2y]

scene at 30:15 Why metal basket was negatively charged? I think positive charge induced by cat fur flows into metal basket. Was metal plate on the glass negatively charged at the moment Dr.Lewin touched the metal plate?

[@prashanthbhavanihebbar771]

Beautiful lectures by sir Lewin ....

[@lubanacholasseri5118]

You are the one who made me a physics lover. THANK YOU SO MUCH SIR

[@lecturesbywalterlewin.they9259]

:)

[@lubanacholasseri5118]

I am from India..

[@surajpradhan8606]

The coolest professor on earth.

[@poojyadav7442]

the force line must be perpendicular to the equipotential then the forming surface eventually forms a sphere?

[@cayezara8110]

Very conceptual lecture! Makes me love Physics.

[@lecturesbywalterlewin.they9259]

Glad you liked it!

[@indiarocks9189]

That brooch on the shirt is perfect❗🔥🔥

[@mcNakno]

If you hold a metal key while doing electrophorus and use that to ground the metal plate it will be less painful, since the charge travel through all of the skin that is in contact with the key instead of the infinitesimal area on your finger when doing it without a key.

[@lovkushmishra2602]

Sir you are the best physics professor that I have ever seen

[@lecturesbywalterlewin.they9259]

Wow, thanks

[@guilhemescudero9114]

At 42:24 , if we move that inside charge +q at a speed near the speed of light, do you think the charges of the conductor has the time to rearrange themself to keep a uniformly distributite outside charge? I said that because the -q charges at the inner surface will have to rearrange with respect to the position of the inside charge +q, since a charge move there is an electric field. Therefore it will change the configurations of its nearest neighbours charges. Does the outside charges (by a chain reaction) have "the time" to rearange instentenatly also at this speed? Thank you

[@lecturesbywalterlewin.they9259]

Maxwell's eqs at relativistc speeds www.hep.princeton.edu/~mcdonald/examples/maxwell_rel.pdf

[@shouvikmondal1977]

Sir, l am from India.I love all your lectures.They make me love physics.The demonstrations are too tough to do in a 50 minutes class.But you did it very well.Before I heard of your lectire, I wanted to be a scientist.But, now I want to be a teacher like you.Thank you sir, giving these high quality lectures free of cost.

[@lecturesbywalterlewin.they9259]

:)

[@shouvikmondal1977]

@@lecturesbywalterlewin.they9259 Thank you sir.

[@name8166]

@@lecturesbywalterlewin.they9259 Respected sir, I'm from India. And, IITs are not the best. Most job seekers go to IITs. If you want to see best then, please go to IISC Bangalore, IISERs (There are 7 IISERs in India), IACS Kolkata, TIFR, NISER, Bose Institute, Saha Institute of Nuclear Physics and all Central universities of India.

[@pantheraonca3635]

Professor Lewin, I have purchased the book you used for 8.02. I have a question on doing problems from the book. What problems does Problem 1.3 Continuous charge distribution. Giancoli 21-49 refer to?

[@lecturesbywalterlewin.they9259]

I do not remember

[@canned_heat1444]

I am very happy I took 18.02 before this course! Makes it very intuitive.

[@lecturesbywalterlewin.they9259]

yes that helps If you ever take my 8.03 course, do 18.03 first!

[@canned_heat1444]

I have already taken 18.03 and will most certainly take 8.03. Thank you for the advise! Will have to brush up on fourier series.

[@lecturesbywalterlewin.they9259]

I cover Fourier series in one of my 8.03 lectures with nice demos

[@canned_heat1444]

Great!

[@MuhammadWaqas-fc3db]

When the metal plate is brought in contact with the rubbed glass which has excess of +ve charges, the lower side of the plate gets excess of -ve charges while the upper side of the plate has excess of +ve charges. You create a path for electrons to flow from the ground onto the upper side of the plate, by touching it thereby rendering the plate with a net -ve charge which is then transferred off to the containter. Am I correct in my explanation?

[@lecturesbywalterlewin.they9259]

google "electrophorus"

[@atharva5257]

Professor Lewin.. 50:00 .What if at the end of the lecture , you put one foot at ground and another in contact with cage..?

[@Miguelin12]

This is wonderful. This man is spreading knowledge on KZbin like I spread butter on my morning toast.

[@Tikorous]

Loudly with lots of chalk and hair? You make breakfast weird

[@surajpradhan8606]

The coolest professor on earth..

[@chanakyasinha8046]

To me its intuitive, as i see the charge arrangement on conducting surface like forces between them, they cannot lie inside, in that case they will feel much greater force than it were outside on the surface, the forces gives intuition. In that heart shaped conductor, there will be more charges on the outer curvature than the curve thats protruding in.

[@pragati6218]

You are fabulous. You are amazing teacher.

[@KeithandBridget]

Not just educational, but entertaining too.

[@anjaliraju6679]

Sir, what would happen if we place a conductor with a charge of +q inside it's cavity in an external electric field ? Since the electric field inside a conductor is always zero. There will be a charge of -q and +q induced in the inner and outer surface of the conductor because of the charge in cavity. But if the conductor is itself placed in an electric field, wouldn't there be a change in the total number of charges on the outer surface of the conductor? If so, then wouldn't we loose the information about the enclosed charged?

[@carlosrodriguezronchel1605]

You play in another league professor, truly amazing

[@lecturesbywalterlewin.they9259]

Wow, thanks!

[@Raudcu]

Excelent Course! I'm from Argentina. I've the following question: How "imperfect" can the cage be? I mean, the electrostic shielding, when yo explained it, and when it's explained in every other course, is with closed hollow conductors. But in practice one uses meshed cages. So, is there a parameter on how big the holes can be? Thank you very much!

[@lecturesbywalterlewin.they9259]

+Lucas Pili how good the shielding is depends on the frequency of the EM waves. If there are openings in the material of a but 1 cm then radar waves will be able to get through. Visible light can also get through. but EM radiation with a wavelength of >10 cm will not get through. Another issue is the thickness of the metal. If it is too thin for a given wavelength, then it can also leak through. Look up the words "radiation depth".

[@Raudcu]

+Lectures by Walter Lewin. They will make you ♥ Physics. Right. I understand. But what happens with an electrostatic field? How big can the holes be? Thanks again!

[@lecturesbywalterlewin.they9259]

+Lucas Pili look up "EM radiation depth"

[@Raudcu]

+Lectures by Walter Lewin. They will make you ♥ Physics. I looked it up. But it's all for EM waves. I found the skin effect for conductors and the skin depht, which is frequency dependent, and get's bigger as the frequency gets lower. But in the case of an electrostatic field (w=0), it would mean an infinity depht what makes no sense. Instead if i use the previous argument of the holes being smaller than the wavelength, it would mean that i can have really big holes for an electrostatic field (lambda=infinity). What i'm not seeing? Thanks!

[@lecturesbywalterlewin.they9259]

+Lucas Pili electrostatic shielding is much easier than shielding from EM radiation. If the magnetic relative permeability is very high (it is about 10^5 in mu-metal) not much is needed to shield perfectly. The lower kappa is the thicker the shield will have to be. en.wikipedia.org/wiki/Mu-metal

[@anuskajajoo8023]

Hello Professor. Why were you touching the instrument that you used to transfer the charge to the hollow cylinder from the cat fur rubbed glass slab?

[@lecturesbywalterlewin.they9259]

google electrophorus

[@studywithjosh5109]

I’m but confused with the heart conductor example. Is he saying charge it positively and then touch it with your hand, or touch it with something that has a positive to charge to make it positively charged?

[@asgeirnilsen6752]

Is it OK to draw lines with arrows to show potential between the plates?

[@keshavanand1230]

Sir which book can be used as a reference book for the lectures?

[@parasmahajan09]

Sir please help me I'm not getting the following... Do the hollow conductors shield the inside cavity from the influence of the outer static electric fields in the case if we have net charges inside the cavity of that conductor i.e. Do those net charges inside the cavity of the conductor remains shielded by the influence of the outer static fields ..?

[@lecturesbywalterlewin.they9259]

>>> in the case if we have net charges inside the cavity of that conductor>>> You can charge your conductor with a cavity but in static situations all your charge will go ti the outside surface of the conductor. In static situations the E-field inside the cavity of conductors is everywhere ZER0. Thus there can be no charges inside the cavity of a conductor unless you glue them in place and hold them there.

[@bethsuni4011]

Please let me know if I'm mistaken about the electroforce at 30:00 You first rub the glass plate with the cat fur. It charges the glass positively. By putting the metal plate on top of it, the positive charges distribute themselves on the metal surface as it is a conductor. When you lift it up, it is charged positively. When you touched the metal container, the positively charged metal plate attracts the negative charges. I don't understand why the metal container is negatively charged not why do you have to touch the metal plate (and get a shock) first.

[@lecturesbywalterlewin.they9259]

google electrophorus

[@riya376]

Interesting and well explained lectures Thanks for giving love for physics❤❤

[@lecturesbywalterlewin.they9259]

It's my pleasure

[@riya376]

@@lecturesbywalterlewin.they9259 Hey sir ,I am your biggest fan You know that I hate physics but when I started learning physics with you I just love physics and this is because of you❤❤ Thanku sooo much Professor

[@wntu4]

Hello Dr. Lewin. I am struggling to understand a couple things about electrons. By what process do they (and the charged sub atomic particles) become polarized? #2 From where do free electrons bouncing around in a conductor derive the energy to keep going? Thank you!

[@lecturesbywalterlewin.they9259]

watch my lectures or use google

[@wntu4]

Lectures by Walter Lewin. They will make you ♥ Physics. Gee thanks. I did. And I did.

[@iqbaljurist]

Hello Sir, i am curious how is that possible you have unenclosed electrostatic shield? I know that the Faraday cage is meshed as long it is smaller than the wavelength of the wave, in this case radio. But in 45:15 , Wouldn't the electrostatic field enter from the unopened part so the net of E inside the shielding is not zero? The hole is quite big though. Also, could we able to calculate the minimum thickness of the shielding (ie. using aluminium foil), i assume that we would use the concept of Gauss ' but i have no further idea about it. Thank you Sir.

[@lecturesbywalterlewin.they9259]

google www.google.com/#q=meshed+wire+Faraday+cage&safe=active&tbm=shop

[@sarthaksharma9322]

Hello Professor good evening , hope you are well and good , I have a question so at NY first attempt to find potential gradient , I first started with vector dot products i.e the work equation ( integral of F.dr , then I got reduced to scalars , now at the end I get E=-dv/dr , now everyone says that -ve indicates the direction of field , and I know in my head that its kinda like slope of tangent which can be -ve or +ve , but all the vector stuff has ended and now this E in the final equation represents magnitude only because directions were gone at the moment I opened my dot product so how this -ve links a magnitude to a vector direction , I am getting crazy at this and trying to solve it for months , but couldn't come up with a satisfying explanation , can you please help me?

[@lecturesbywalterlewin.they9259]

>>>E=-dv/dr , now everyone says that -ve indicates the direction of field>> yes it does. E_x=-dV/dx, E_y=-dV/dy, E_z=-dV/dz. If E is only a function of r then E=--dV/dr and it is in the direction (or opposite direction) of the vector r.

[@shilpdhande4340]

can someone elaborate the heart problem? I was fine untill then but could not understand the explaination. Also is the heart a 2d i.e surface?

[@blee6117]

Hi Professor. Regarding E field and gravitational field are they ideally moving stright. Ofcourse fields can bend. My question is field lines are moving stright or they oscilate at very very high frequency so we see them as a stright lines?

[@lecturesbywalterlewin.they9259]

E-fields can have complicated shapes. I cover this in detail in my 8.02 lectuers

[@shiva_iitkgp]

Sir you are awesome Love from INDIA

[@giandimayuga7081]

Good afternoon Professor Lewin, I have been enjoying viewing your old lectures as well as your homework tutorial sessions. I really liked the way you demonstrated the behavior of electric fields through the method of electrophoresis. I have few quick questions regarding electric field, and electric flux using Gauss law as well electric potential. If the electric field is a 100% on the surface of a conducting sphere, and 0% or very close to 0% deep into the very center core aka (a Faraday cage). Does it work the same way for a solid conducting sphere of charge that is not hallow on the inside, or does the sphere need to be completely hallow on the inside. My 2nd question is, does non-uniform charge density occur both on fully solid and hallow insulating spheres of charge? My 3rd question is when we receive a static shock or are hit hypothetically by a bolt of lightning, is the spark voltage or electric potential, and does the spark only take place when an electric field is developed between 2 oppositly charged objects (+)&(--) or can the spark occur between to objects with the same polarity of charge? Thank Professor Lewin in advance and wishing you a Happy Thanksgiving.

[@lecturesbywalterlewin.they9259]

I cover this in my 8.02 lectures

[@rishu096]

Sir you touched the metal can directly with the electrophorous,which should also make the can positively charged. By induction it would have been negatively charged

[@marygonsalves2323]

Thank you from India.

[@nav_819_]

Sir I have a doubt. I made a closed conducting body with a closed steel vessel and attached a wire (having insulation) within it and took it out through the side of its tight cap. Then I attached a knife to this body(just for capturing the spark like lightning arrester) and then passed a small current through it with the help of a gas lighter. I got a slight shock from its outside and what surprised me is I got the same shock from the wire which was taken from inside the conductor. How could this happen? Is it against electrostatic shielding?

[@lecturesbywalterlewin.they9259]

ask Quora

[@NitishYadav-rp4yj]

I'm from India preparing for jee these lectures are great .they help me a lot

[@mukeshsuman9306]

jee 2024 ?

[@bryamayvar6590]

Truly inspiring

[@NamNguyen-gd2yf]

I just happened to watch this lecture on Valentine's day!

[@dr.sciencesc.d3088]

Hello Professor Lewin, if no charge goes in the inside of the Faraday Cage, why is it that the bottom of the inside of the Faraday Cage must be insulated?

[@lecturesbywalterlewin.they9259]

+Dr. Science Sc.D The bottom also has an outside. Charge will be there. If we do not insulate the bottom, the electric charge can escape and that would be a cheat.

[@five5059]

Sir, Is there any of yours 8.04 and 8.05 courses to be find? I looked all over the internet and I couldnt find any

[@lecturesbywalterlewin.they9259]

MIT OCW has 8.04 and 8.05 on line

[@five5059]

Lectures by Walter Lewin. They will make you ♥ Physics. Thank you a lot sir :)

[@adycalin92]

If we have high voltage inside the faraday cage (or maybe we get an electric discharge on the cage's wall) and someone touches the outside of the cage will he get electrocuted by the positive charge on the outside ? If the answer is yes, what if the cage is grounded ?

[@lecturesbywalterlewin.they9259]

+Adrian Calin The capacitance of a normal human Faraday cage is probably about 200 pF. We cannot charge the cage up to very high voltage as there will be discharges on sharp edges. Perhaps you can charge it up to 30,000 V. The charge on the outside would then be approx 0.006 C. Touching the outside would discharge it. You would feel a brief shock but there would be no danger at all.

[@sideswipe147]

reguarding the demonstrationwith the paint can. what happens if you charge the inside surface of the paint can. Will it the charge still only be on the outside of the can?

[@lecturesbywalterlewin.they9259]

yes the charge will move to the outside surface if the can is a conductor.

[@patrickmayer9218]

47:54 cannot figure out what he said that was so funny, "A woman who opposes a bombing"? XD Thanks for the lecture, Dr. Lewin! This was one of your best yet!

[@kumaranunay3058]

Sir, in the case when we put charge inside the cavity...will that charge get stuck on the inner surface if it isn't placed at the centre of the spherical shell..??

[@lecturesbywalterlewin.they9259]

question ill-defined. If I have a conductor with a cavity and I place -q charges inside the cavity at random locations, then the - charges will move till the E-field inside the cavity and inside the conductor will become zero. The -q charge will be at the outer surface of the conductor. Use Gauss' Law!!! I cover all this in great detail in my lectures and in my Help Sessions.

[@jimmyjam6197]

Does anyone know if the assignments he’s talking about are publically available. The linked problems don’t contain a problem 2.1 that he talks about around 37:00

[@jimmyjam6197]

Found it, it’s in the link from the next lecture

[@sandhugaurav5619]

Hello Sir what would be the trajectory equation of equipotential surfaces between two identical positive charges separated by an appreciable distance?

[@lecturesbywalterlewin.they9259]

those curves are very complicated. Check Jackson - maybe he discusses it.

[@alekhsharma816]

I think I know how you charged the paint can when you touch the metal charges flow from glass to metal because of potential difference and when you touch the paint can with the plate the charges go to the paint can. Some charges are lost that go from your body to ground. Please tell if I am correct or not professor lewin. 30:10

[@alierenozylmaz3488]

Electrons flowing to metal from his body. + charges attracts - charges that cames from the ground. + charges cant go from glass to metal.

[@parasmahajan09]

Sir please explain... We know that if we have a conductor with a cavity and there's no charge inside the cavity then this conductor acts as a protective shield (faraday cage) which shields the inside cavity from the external static electric fields but now if we place a net charge inside the cavity, does this conductor with cavity now acts as as a faraday's cage for the charge that is placed inside the cavity?

[@lecturesbywalterlewin.they9259]

You can charge your conductor with a cavity but in static situations all your charge will go ti the outside surface of the conductor. In static situations the E-field inside the cavity of conductors is everywhere ZER0. Thus there can be no charges inside the cavity of a conductor unless you glue them in place and hold them there. I explain this in my lectures. PLEASE watch my lectures.

[@muhammadushaukat2143]

Hello Sir, I have a question at around 45 minutes. When you turn the generator on, the surface of the bucket conductor is equipotential. That means that the the surface of the conductor is perpendicular to the electric field lines, right? The second question is that if the generator is negatively charged, I have to do more more work to get an electron to the right side of the bucket and less work to get it to the left side. This means that the potential is higher on the right and so electrons move from the lower potential to the higher potential. Therefore, should not the right side then get negatively charged and the left side positively charged when it comes to distribution on the surface?

[@lecturesbywalterlewin.they9259]

send me the EXACT times (nearest 10 sec) for each question.

[@muhammadushaukat2143]

@@lecturesbywalterlewin.they9259 43:50 - When you turn the generator on, the surface of the bucket conductor is equipotential. Since equipotential surfaces are perpendicular to the field lines, it means that the the entire surface of the bucket is perpendicular to the electric field lines, right? if the generator is negatively charged then as seen by me in the video, the right side gets positively charged and the left side gets negatively charged. Lets says I am bringing an electron from infinity from the left. Now, I have to do negative work to get an electron to the left side of the bucket and then positive work to get it to the right side. This means that the potential is higher on the right and since electrons move from the lower potential to the higher potential, should not the right side then get negatively charged and the left side positively charged when it comes to distribution on the surface? I hope you understand my badly phrased questions. And yes, GOD Bless you Sir for all that you do for your students! I haven't come across any professor yet who goes this far to help student all over the globe! Love!

[@commentor6439]

should the charge on both sides of a conductor equal each other after induction? and if so why didn't the electroscope at 45:00 move back to the original location

[@lecturesbywalterlewin.they9259]

watch the lecture carefully and you will know the answer.

[@shreyachidambaram1990]

I still can't figure out why you had to touch the electrophorous. Could someone explain please?

[@hamidthephysicist6376]

Thank you very much professor .

[@Abhisheksharma-lk4ll]

Professor lewin i had a doubt that why did you consider at 6:12, to imagine that we are in space? Why not earth.

[@Study-if7by]

at the end of video you jumped out of the cage its for fun or is there any reason behind it?

[@sportsman9519]

Amazing lecture sir Love from "INDIA"

[@lecturesbywalterlewin.they9259]

So nice of you