8.02x - Lect 16 - Electromagnetic Induction, Faraday's Law, Lenz Law, SUPER DEMO 

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I can see why MIT are keeping chalkboards as opposed to replacing with hi tech. Your chalk skills are amazing. Great lecture too! Thank you.

Hello once again Dr. Lewin; Your lectures are proving to be a fun and productive learning experience for me. Your passion for physics, your knack for communicating and educating, and the strength of your convictions in the wake of the controversy created surrounding the validity of Kirchoff's Loop Rule, have inspired me to challenge my own understanding of concepts that I've often failed to appreciate. I credit you for empowering and inspiring me to treat both sides of the controversy equally and fairly. It's amazing how so many have attempted to set the record straight and discredit your provocative claim by simply declaring that you are wrong; and then proceed to apply their own spin to the results of your experiment, defending Kirchoff's Loop Rule, and focusing only on your error; while adding nothing toward understanding of the concept of Faraday's law that you were presenting. All of the arguments I've reviewed and studied are convincing enough at describing what we were all taught; but none seem to convey an understanding of your point of view or your presentation, sufficient enough to challenge them. I wasn't looking to be told what I know... or think I know. I was intrigued by the possibility of learning something new. I began dissecting your lecture, hanging on every statement and visual aid presented until I became certain that I understood you every step of the way. At 38:36 in your lecture, you make the statement "So far so good!", and I am in complete agreement with you up to that point, including your corrected Ohms Law equation (at 35:59) up through and including your statement at 40:28 "... and now it's not so simple... because there's no battery." This is where you switch from a conservative model to a non-conservative model, at which point the difference between them becomes quite clear and intuitive. Aside from correcting your Ohm's law error, you never discovered nor took note of it through to the end of your lecture. I'm speculating that the error may have been steering your thinking in the moment and stayed with you; but maybe not. Continuing from 40:28, you follow with "and so now when I go from point D to point A... I don't have the "1" and therefore I now find -0.1 Volts... I find a totally different answer." This is where I became disconnected, and asked myself the question "How can the voltage drop across two resistors be opposite in sign when the current is flowing in only one direction? So I listened further for the answer... As you stated... this is not intuitive. At 44:20 you make the point: "keep in mind that with non-conservative fields, it depends on the path". That statement seems intuitive and clear to me, and I interpret this as the encircling path of the loop with the induced emf flowing in one direction only at all points around the loop; but changing direction in concert with the building and collapsing of the magnetic field that induces the emf in the loop; as observed in your multi-turn loop demonstration using a solenoid and center reading Galvanometer. In the schematic drawing shown in your lecture notes, you correctly show the loop current flowing clockwise inside the loop, with current flow from node D flowing down through R2 and down through voltmeter V2 to node A. On the opposite side of the loop, you correctly show the current flowing up from node A through R1, and up through voltmeter V1 to node D. Missing in your drawing is the polarity of the connected voltmeters. Your schematic is accurate and clearly indicates that the the polarity of the voltmeters, and the voltage drops across R2 and R1 are reversed; as they should be when diametrically opposite the loop from each other with current always flowing around the loop in the same direction. Therefore experimental measurements must observe this convention; with the positive side of voltmeter V2 connected to point D, and the positive side of V1 connected to point A. Assigning the the polarity of the voltmeters, consistent with the convention used in your schematic will show that V1 = + 0.1V, and V2 = +0.9V, with their sum now equal to the 1.0V induced emf in the loop. Your experiment demonstrates and satisfies all of the supporting findings of Oersted, Faraday, Kirchoff, Lenz, and Ohm without conflict. Additionally, it also demonstrates that the validity of Kirchoff's Loop Rule is independent of conservative and non-conservative fields. A slight rearrangment of how the loop is presented, may also make it a bit more intuitive to conceptualize. Unfortunately; I am unable to upload my rearranged schematic drawing to RU-vid. Best wishes and respectful regards; Gary O'Neil

If everyone had a teacher like you, learning would be not only easy but enjoyable :) Thank you for all your lectures.

Prof Lewin. Your lectures are among the best science lectures ever delivered anywhere. The MIT students were incredibly lucky that they got it live,but thanks to the marvel of the internet, practically anyone anywhere in the world (provided they understand English) can learn from your incredible ability to teach. My deepest respect for you and a deep bow of gratitude.

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For those that keep saying that you wished he was your teacher when you were younger or whatnot: look at the bright side, that it is possible that he is now a teacher to everybody is a beautiful thing. It's a wonderful time to be alive.

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Sir walter lewin I am in class 10th from India.I was very bad in physics and didn't liked it but because of you I am addicted to physics that even I am now able to understand these topics Thank you very much.And we all students are gglad that we have the greatest teacher of all time.

Lectures with applied demos and derivations are always better than an entire lecture of numerical problems. Great lecture!

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The whole Incident with ElectroBOOM was so amusing. I'm happy it happened just before I watched this lecture. Understanding the confusion helped me to digest the topic better. So thank you Dr Lewin and ElectroBoom. :)

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36:02 ......made me remember that anythings possible! I absolutely love all of Walters lectures!

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At MIT : WHAT!! homework too long?? Ok i cut out 2 questions u do only 7 At Schools : WHAT!! homework too long?? Ok rewrite it 2 times and from tomorrow 10 questions instead of 8 + detention+ guardian call+1 week suspension+ 10 point deducted from you final grades for complaining...

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Go to 5:00 for actual lecture.

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0:33 "If you are very unhappy with your recitation instructor, you are complete IDIOTS, if you stay in that recitation!" I truly love this!

"Concepts is what matters." (3:16)

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Dr. Emmett Brown, could you PLEASE take me back to the future so that I can come to your classes in real life...

The oscilloscopes form a second conductive loop around the energizing coil. Although an oscilloscope is concidered to be a voltage measuring device, in this case they are measuring the current that flows in a clockwise direction around the loop that they form. The righthand oscilloscope see's current flowing into its positive terminal, the leftthand oscilloscope see's current flowing into its negitive terminal and so shows a mirror image. The different amplitude of the two displayed waveforms is caused by the different values of the resistors in parallel with the one megohm resistance of each oscilloscope. If you simply move one oscilloscope to the other side of the coil without changing the connection points of that oscilloscope, both oscilloscopes will now display the same waveform.

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"Kirchoff is for the birds" truer words have never been spoken

5:25 is changing electromagnetic field

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There'll also be an induced emf in the circuit which when added to the other potential differences through the resistors should add up to zero ensuring that KVL holds.

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Sir I am a class 10th student in India.Here I have enrolled in a institute to guide me to get in IIT colleges.They are not able to explain Lenz law to me so I thought to search for it on youtube and found your video.I knew you from 2 years and thought that it might be difficult for me to understand it but it was quite easy.

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