This 18 minute Mini Lecture is a MUST

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

Ай бұрын

Watch All 18 minutes, you will greatly benefit from it!

Пікірлер: 90

@mohdhashir3840 Ай бұрын

Hope electroboom vs walter lewin doesn't start again 😊😊😊😊😊

@kartikeysingh3182 Ай бұрын

WOW! Loved this mini-lecture Professor! Thank you for clearing the difference between Faraday's laws and KVL. I request you to please keep uploading this type of mini-lectures. Really enjoyed a lot. One last thig to say..... those real life examples (torch and radio) are really amazing!

@amitkumarchejara6042 Ай бұрын

A very very imp concept explained!! Thankyou for this eye opening video!!

@carlospoccia5066 3 күн бұрын

Thank you very much for shedding light, professor, greetings from Argentina

@markitsche987 Ай бұрын

You made my day today, Professor Lewin. Thank you for this lecture.

@lecturesbywalterlewin.they9259 Ай бұрын

Glad to hear that!

@amitarishi Ай бұрын

Hello Hello Hello Professor ❤Walter! I am very grateful to you for changing the way I view the world and understand physics. I will be giving the JEE and would be thankful for your well wishes

@amitkumarchejara6042 Ай бұрын

Thankyou sir for making a whole video on the question I raised in your thired previous video...Keith norman's solution

@hanslepoeter5167 Ай бұрын

Thanks for explaining again sir. I understand a little bit better than before. Maybe. I like to think of a self inductor as a component where the voltage falls over, even if the resistance is zero. That's a simplified view and I'm aware of that but it allows for a simple analysis of circuits where KVL hold's. There are times when this simplified view is not enough, typically when the electromagnetic field of a self inductor interferes with other component's or even other devices. It can be very painfull if we engineer something and that is causing a problem.

@lecturesbywalterlewin.they9259 Ай бұрын

>>>>That's a simplified view and I'm aware of that but it allows for a simple analysis of circuits where KVL hold's.

@jdubruyn Ай бұрын

These mini lectures are priceless professor. They can help us mortals to catch concepts that may have taken a lifetime or more🙌🙏 Please look after your health professor - Omega3's, Vitamin D(requires Magnesium(Magnesium Citrate)), Astaxanthin, Vitamin B's, Calcium(very important for the nervous system) and Vitamin C - I think these are most important. Siim Land did a video a few days ago on what he takes if you want to look at it prof... like Siim says at the end of his video -stay optimized stay empowered😉⚡

@PaoloMassa-qb7pb Ай бұрын

Good Morning professor Lewin, you are the best teacher that each student can desire to meet. Congratulations for all your job eng. Paolo Massa from Italy

@lecturesbywalterlewin.they9259 Ай бұрын

Wow, thank you

@steveh1273 Ай бұрын

Very cool lesson.

@lecturesbywalterlewin.they9259 Ай бұрын

Glad you liked it!

@surendrakverma555 Ай бұрын

Excellent information Sir. It was never told by any Physics teacher and most books also don't explain it. In circuit theory, Simple KVL gives same answer. But how we get different reading in different directions for same potential points in physical sense? Thanks and Regards

@lecturesbywalterlewin.they9259 Ай бұрын

When there is an induced EMF, then KVL does NOT give the same answer as Faraday. *Potential diff is not well defined anymore whe there is a induced EMF. The integral of E do dL then depends on the path.*

@ayushmansharma-lp8te Ай бұрын

Sir why the light is moves forward Which force push the photons forward???

@lecturesbywalterlewin.they9259 Ай бұрын

light has no rest mass but it does have momentum and Enegry. All massless particles (photons) must move with the speed of light (use google).

@FACTFLOWbySHIVAM Ай бұрын

Sir i got inspired by you in physics and you make this intrest more and more always thanks for that my respected inspirational professor and love ❤ from india

@lecturesbywalterlewin.they9259 Ай бұрын

All the best

@Ankit-ni8bc Ай бұрын

Love From India ❤️❤️❤️❤️

@kenjideboutte1484 Ай бұрын

Professor, I completely understand the explanation but I always had one big question, if there cannot be an electric field in the coil (= ideal conductor), how is application of Faraday's law in differential form explained? Curl(E) = -dB/dt, if the magnetic field through in the space through/around the coil is changing, this laws says that an electric field has to rotate in the plane perpendicular to the changing magnetic field. This electric field is passing through the loops of the coil, what is opposing this field to make the electric field in the ideal coil zero?

@lecturesbywalterlewin.they9259 Ай бұрын

you misinterprete Maxwell's eqs. A current can flow through a super conductor. That's what the accelartors in Geneva are all a bout. But no E-field can exist in a super conductor as it has no ohmic resitance.

@kenjideboutte1484 Ай бұрын

@@lecturesbywalterlewin.they9259 Thanks for your answer, I still don't see the misinterpretation in curl(E) = -dB/dt... Where does the induced electric field constitute itself?

@kanishkamajumder7259 Ай бұрын

I love your physics videos

@kanishkamajumder7259 Ай бұрын

SIR, I have a doubt

@kanishkamajumder7259 Ай бұрын

Can an electromagnetic wave be deflected by a magnetic field ? Explain.

@lecturesbywalterlewin.they9259 Ай бұрын

use google - EM waves are formed by electric and magnetic fields but are not deflected by them, and also they can be deflected by gravitational fields. Light (electromagnetic wave) has an electric and a magnetic field and should thus deflect a compass needle during daytime.

@kanishkamajumder7259 Ай бұрын

@@lecturesbywalterlewin.they9259 thank you sir

@adityachaudhary4948 Ай бұрын

Hello professor hope this comment finds you well there and I wanted to ask that whether electric charge is an extensive property or intensive property and how much appropriate this classification would be?

@lecturesbywalterlewin.they9259 Ай бұрын

question unclear - use google

@jackbidnik9642 Ай бұрын

Prof. Lewin, I do not at all doubt your explanation of the circuit analysis of Faraday's law, but I am interested in how the ambiguity with KVL arises. I pose this question: Suppose we have only a battery and a switch, not even a circuit. Then the point A, which is on the far side of the switch from the battery, when the switch is open has zero potential. But when the switch is closed, point A, according to convention, has a potential of +V, the same potential as the + terminal of the battery. Is this not also the case if we insert the battery and switch into the inductive circuit you have shown?

@lecturesbywalterlewin.they9259 Ай бұрын

Apply the closed loop integral on any closed loop. what you are suggesting are no closed loops. KVL only works if there is no induced EMF. Faraday always works also in cases that Ldi/dt = 0.

@jackbidnik9642 Ай бұрын

@@lecturesbywalterlewin.they9259 Thank you for your reply. I only mentioned the isolation of the battery and switch from the circuit to establish the voltage in that case, then to reinsert it as you have it and enquire if the voltage at point A is different in the closed circuit case. I realize the potential is a varying thing when there is an inductance in the circuit, just wondering how it changes at A as the switch is closed. I have no partiality to KVL at all in this case. By the way, I was most impressed with your demonstration in class of the different readings on different sides of the parallel resistors.

@lecturesbywalterlewin.they9259 Ай бұрын

@@jackbidnik9642 Watch my video again; I cover (also in Lectire 2) what happens when you close the switch. I even draw pictures how the current changes, depending on the values of L.

@woodcoast5026 Ай бұрын

Hi Walter My comment is not about the applicability of KVL to the circuit , however there is certainly an electric field along the wire of the self inductor , by the definition of the electric field there is an electric field along the wire , because there are charges there experiencing a force and that is the definition of an electric field.

@lecturesbywalterlewin.they9259 Ай бұрын

There is NO E-field inside a suerconductor. *Thus the intergal of E dot dL through the superconducting wire of the inductor from one end to the other is always ZERO!*

@woodcoast5026 Ай бұрын

@@lecturesbywalterlewin.they9259 Regardless of the low or Zero resistance the electric field is there E = F/q . Charges along the wire are experiencing a force along the wire and so there is by definition an electric field along the wire. Ohmic resistance along a wire is not a requirement for an electric field to be located along a wire.

@lecturesbywalterlewin.they9259 Ай бұрын

@@woodcoast5026 There is NO E-field inside a suerconductor. *Thus the intergal of E dot dL through the superconducting wire of the inductor from one end to the other is always ZERO!* End of story

@The_Green_Man_OAP Ай бұрын

@@lecturesbywalterlewin.they9259 I think you keep getting this from people b/c they do not understand why E=0 in a super conducting inductor.

@copernicofelinis Ай бұрын

Only when you consider a real conductor with finite conductivity there will be a tiny electric field inside the inductor. A field compatible with Ohm's law in its local form j = sigma E. In the case of a perfect conductor sigma is zero, so the electric field goes to zero. The surface charge that makes the field zero INSIDE the perfectly conducting inductor (or very small inside a real conductor) are also responsible for the nonzero field outside the inductor. This field outside is what makes a voltage appear in the space between the terminals and between turns (but only for paths that form, with the conductor, a one or more loops around the changing magnetic flux).

@luiesherosaki4797 Ай бұрын

Tomorrow 4th April which is the beginning of the smiles of thousands and cries of around hundred thousand of Indian 12 grade students hope you know what am taking about

@lecturesbywalterlewin.they9259 Ай бұрын

1897 April 4 (not Febr 4) Hugew Earthquake in India

@luiesherosaki4797 Ай бұрын

@@lecturesbywalterlewin.they9259 thanks for the reply sir ,,,, Well I was about to say that the JEE MAINS phase 2 are starting from tomorrow which is like an earthquake to most of the students 😅😅

@yasir_wayne Ай бұрын

@@luiesherosaki4797 😅 , You should Post the same Statement on or Before 26th May, He may respond Better then this than/ Aware of! Hopefully You got it :D

@user-tg5hc9dw5c Ай бұрын

Good Morning sir 🙏.. I am Avanish Singh moving in class 11 as an jee aspirant . I am so happy and excited but I want to join offline coaching and my family doesn't agree because of economical problem. Sir I request you to help me. Sir please help me otherwise my IIT dream will broke. Sir please help me as much you can. I will so grate full to you in my whole lovely life. 🙏🙏 or tell me about some way to overcome this problem.

@lecturesbywalterlewin.they9259 Ай бұрын

Watch all my 94 MIT course lectures. Start with 8.01, then 8.02, then 8.03. Do all the homework and take all my exams. *I guarantee you that you will then do very well on the Physics portion of any freshman college or JEE exam* You will find all information you need on this channel in three playlists "Homework, Exam, SolutionsY & Lecture Notes". 8.01 & 8.02 will each take about 200 hours, 8.03 about 250 hours.

@user-tg5hc9dw5c Ай бұрын

But sir for chemistry and maths?? I think alakh panday sir will help me if you help me. For offline course at my nearest center varanasi i.e. BHU.

@Curious_Mind_3.14..... Ай бұрын

Sir iam your biggest fan from india im currently 16 years old watching you from 1 year can you tell me how can i become like you

@abulkhayer4898 Ай бұрын

I'm from class 9th sir...and I want to know about the topic ENTROPY of Thermodynamics....

@lecturesbywalterlewin.they9259 Ай бұрын

use google

@MrKinyodude Ай бұрын

Engineers use KVL because it is handy tool for solving loop currents. Engineering teachers never even mention that Faraday's Law is the underlying basis for KVL. The confusion shows that engineers are not physicists. Physicists show what's possible, engineers build.

@lecturesbywalterlewin.they9259 Ай бұрын

If engineers *always* use KVL then transformers and internet would not exist and planes could not fly. *Luckily the Physicists call the shots!*

@MrKinyodude Ай бұрын

@@lecturesbywalterlewin.they9259 Engineers love shortcuts, so they made KVL work on transformers too. SInce Faraday's Law always work, transformers can just be represented as an element in a circuit. Then power engineers invented another shortcut called per-unit calculation where transformers disappear in the calculation for voltages, currents, and power. So thanks to Faraday's Law, it made some shortcuts possible.

@lecturesbywalterlewin.they9259 Ай бұрын

@@MrKinyodude I am glad to know that engineers had to jump through a few hoops to still get the right answer. Physicists, who would use Faraday's Law, would not have to jump through any hoop and they would never have any doubts about their correct solution.

@vibhortripathi8709 Ай бұрын

Prof my doubt is regarding ur previous lectures at MIT. Back in 801x while you were teaching mechanical physics u took certain uncertainties in ur problems . How were u so certain of ur uncertainties like how did u assume the uncertainties like when ball hit a floor the uncertainty would be about 5 milliseconds in time. That part is a bit confusing 😅😅.

@lecturesbywalterlewin.they9259 Ай бұрын

kzbin.info/www/bejne/f2XGiZigideSacU

@vibhortripathi8709 Ай бұрын

Thanks prof

@user-xf3gw6fo2n Ай бұрын

After watching the 18 min lecture, I go to the 50 min lecture 16. And now I am going to look-up what is "conservative filed"...

@nuclearrambo3167 Ай бұрын

it means curl is zero, in vector analysis sense

@arpit- Ай бұрын

Sir please read my question If we connect a wire of zero resistance across a battery with internal resistance zero Will current flow in the wire as all points on the wire will have same potential. ,?

@lecturesbywalterlewin.they9259 Ай бұрын

This is one of my Physics Problems - go for it and also read the solution. Current will flow but NOT through the wire

@Ogdivyansh Ай бұрын

Holy skibidi!

@legacygamemaker9800 Ай бұрын

Dear Mr. Lewin, a Chinese high school student, you made me go from hating physics to loving physics. China's terrible exam-oriented education😢

@justin_other_kayaker Ай бұрын

Love the music. Wonder who was the artist, and what was the title and year😂

@saumyameena2008 Ай бұрын

1st from India please reply me I wanna know how to focus on studies and my weakest subject is physics please help me sir

@lecturesbywalterlewin.they9259 Ай бұрын

eat yogurt every day but *never on Fridays* That worked well for Einstein and also for me.

@omicronsrule6565 Ай бұрын

😂@@lecturesbywalterlewin.they9259

@sb-sm8ib Ай бұрын

@@lecturesbywalterlewin.they9259😅

@user-cz9ou4ue7v Ай бұрын

Taking by your name, I'll issume you're a 10th/11th(to be) grader, here are some things you can consider following 1. Concept, learn it, there's no alternative. 2. Formula derivation, wherever possible, get the hold of how the formula is derived, it will increase the number of sums you can solve. 3. Don't take breaks when you're tired but schedule the breaks and stick to it firmly (even if you wanna continue studying, take the 5 min break)

@eventu08 Ай бұрын

A warning to these climate people that think batteries can run the world.

@michaelbruning9361 Ай бұрын

I also work with Faradays law, but in contrast of you i imagine that under certain conditions there is and must be an E-field in a coil. If you have AC voltage, the resistance of an ideal coil is not zero, it is w * L. The contribution to the E-field from Faraday law - L * di/dt comes from the coil with the inductance L. Depending on whether the magnet field in the coil is increasing or decreasing, the E-field of the coil can support or counteract the E-field of the powersupply. If you think, that there is no E-Field in a coil, how would you explain, that if there is a time changing B-field inside a coil, in one moment the left side of the coil is negative charged and the right side positive and some time later the left side of the coil is positive charged and the right side negative ? That is only possible, if there is an E-field in the coil, which accelerates and decelerates the electrons, so that they move from one side of the coil to the other side and back. A simple situation to demonstrate, that there can be an E-field in a superconductor is: A 1m long cylinder with 1mm diameter in direction of the y-Axis is moved with a velocity v in direction of the x-axis and there is a B-field in direction of z-Axis. Then you will get a voltage between the endpoints of the wire and you can calculate the E-field in this wire with the equation q*E = q*v*B. You can watch my video (and the following lectures for the induction law). kzbin.info/www/bejne/gGi6iYKshrR-b6c

@michaelbruning9361 Ай бұрын

This idea for the derivation of the induction law (if you watch the following videos) comes from my father who unfortunately died 2017 and was also a great physic school teacher. You can also download the software for windows for free.

@georgejetson4378 Ай бұрын

Definition of IDEAL coil is ZERO ohmic resistance!

@lecturesbywalterlewin.they9259 Ай бұрын

There is no AC electrical current resistance. *There is no resistance in a superconductor, period.* What the statement means is that you do not lose electrons to heat while transferring electrons through the superconductor.

@lecturesbywalterlewin.they9259 Ай бұрын

@@michaelbruning9361 Resistance and reactance are the properties of an electrical circuit that opposes the current. The main difference between reactance and resistance is that *resistance measures the opposition to a flow of current,* whereas reactance measures the opposition to a change in current. *A superconducting inductor has zero resistance*

@michaelbruning9361 Ай бұрын

@@lecturesbywalterlewin.they9259 I never lose electrons to heat (charge is conserved). Electric energy is transfered into heat energy. I agree with you, that a superconductor has no ohm resistance. The correct word is probably reactance. In germany we say also inductive resistance, so i wrote resistance.