8.02x - Lect 27 - Destructive Resonance, Electromagnetic Waves, Speed of Light
ฝัง
- เผยแพร่เมื่อ 13 ก.พ. 2015
- Destructive Resonance,Breaking Wine Glass, Electromagnetic Waves, Speed of Light, Radio, TV, Distance Determinations using Radar and Lasers
Lecture Notes, Travelling Electromagnetic Waves: freepdfhosting.com/c154c2cbc7.pdf
Assignments Lecture 26, 27 and 28: freepdfhosting.com/20495b808e.pdf
Solutions Lecture 26, 27 and 28: freepdfhosting.com/7759a06b8d.pdf - วิทยาศาสตร์และเทคโนโลยี
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That demo at the end deserves 5 minutes standing ovation. Thank you so much Prof. Lewin for the wonderful lectures.
Glad you liked it!
@@lecturesbywalterlewin.they9259 Dear professor, did you get into any trouble with Harvard afterward?
Hilarious... outstanding!
I was just about to say the same thing lol. Awesome demo!!
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!
Hi, but I am not able to get the homework assignments, I have tried many a times,could you please help .Thanks
A great balance of theory and practice with just a nice touch of humour, thanks
The lectures are so good that I watch them as an entertainment. Thank you Sir.
I love how physicists swap integrals and derivatives without any remark :)
I won't kink shame
@@Tikorous damn you got me man 😂😂😂
Differentiating under the integral sign is allowed.
Dearest professor, Being in your timeline is our greatest pleasure and proud moment. You are an Inspiration to teach and Fall in loving with Subject..Lots of Thanks sir.
These lectures have excellent camera work and the switching is excellent too. I commend your crew on their diligence.
Thanks for posting these videos!!! My physics lecturer was absent for multiple weeks and didn't cover half of what you do! I love physics, and these examples really help me understand the concepts better. (:
if there was a prize nobel in teaching, it would be for you. Thank you very much for your lecture !
Every lecture of his, is a MASTER PIECE !
Absolutely fantastic lesson. Finally I understood how to derive the speed of light!!!
Hi Walter , I am returning to these lectures for the 3rd time , I just love them. Since the first time of watching I have passed all three UK amateur radio exams and your lectures on electromagnetism and related topics certainly helped. Thank you 🙏
Wonderful!
excellent demonstration with the transmitter professor Lewin!
As someone who teaches undergraduate chemistry I watch your lectures and they inspire me ! Unfortunately we cannot do demonstrations with chemistry due to safety considerations, but these excellent demonstrations sure make the lectures exciting ! They are no doubt extremely time consuming to set up - and I can only hope you got outstanding course evaluations :-) By the way, I teach in your home country of the Netherlands - in Maastricht :-)
Hello Mr Walter Lewin, first I apologize for my bad english. it's because I'm french. And you know french people speaks often bad english.
But with your famous science lectures I understand you so well !! You're the best teacher I never had, really I'm fond of your lectures. So tahnk you very very very much for your sharing of your knowledge : it seems so easy to understand with you.
These are the lectures i would never miss!
Thanks for the class!
Happy teachers day to you sir .
You are the most loving and respected teacher for me . You have changed my thoughts about physics, the way of thinking .
Sir here is teachers day in india today .
So happy teachers day to the world's best teacher
What a marvel of invention of velocity of EM waves related to permitivity and permeability and a great Professor Liwen thanks sir
Another great session thanks teach.
Oh, this is so cool! Thank you Dr. Lewin!
You're very welcome!
10:28 an important consideration in the phenomenon of destructive resonance is that rapidly slowing the input frequency of an object which is at resonance causes something akin to the inductive spike in a coil due to a collapsing field. A large shockwave occurs as a result of an interference pattern in the material. This can be seen as water splashing from a dish as the frequency is changed or as a building structure disintegrating the moment an earthquake start to subside.
Strange how I have ideas of things I'd like to learn about purely from guessing the methods others like nikola tesla and I wind up here.
I like this professor, he simplifies but explains throughly. 👌
You are really a great enligtented master in your passion SIR
:)
I think showing your interference with the radio signal was really funny. 😂😊😂😂
:)
Not to mention blaming it on Harvard. Walter, that was a bit cheeky, but I loved it.
Wow 🤩🤩 experiment on resonance is awesome thanks a lot sir 😊
That is the most awesome Radio broadcast ever. I wonder what the power output was from that frequency generator.
The electric field composed with the magnetic field results in a diagonal field. This resultant is the polarization of wave: vertical or horizontal. In certain waves both fields are desphased 90° resulting in a wave with circular polarisation.
Best Physics teacher there ever was
Brilliant, thank you for sharing.
My pleasure!
Legend
Excellent lecture 🙏🙏🙏🙏🙏🙏🙏
I wish I could do TeX markup on TH-cam... I tried solving the students half of the assignment using a similar method and arrived at:
- E0 l = - l B0 w / k ... Which of course reduced to ... B0 = E0/c ... I just wasn't sure if I took the right approach what with minus signs and directions around loops.
Wooooooooo! My brain is melting out my nose....
One of the things they don't emphasize in textbooks, but which everyone should recognize, is that every oscillator has a restoring factor and an inertial factor. And both of those factors are a measure of how much energy the oscillator can store
In the spring, it is the spring constant over the mass. In the string, it is the tension over the mass density. In the pendulum, it is gravity over the length. And in the EM field, it is epsilon over 1/mu.
In each case, you have an (energy storage / unit of displacement) / (energy storage / unit of change). Thus, when you see c presented this way, it is obvious why epsilon is capacitance per meter. It is no longer just a bunch of random looking units. Capacitance is a measure of how much energy can be stored in the electric field. And you also see why my has to be farads / meter. Inductance is the measure of how much energy is stored in the change in the electric field (that is, in the magnetic field).
So one can see, even without any calculus, why a field that works this way would sustain waves.
Amazing !
G.O.A.T
Very good lecture
Prof, great watching your lecture! Did you really do that thing(being on the air) at the end? Or, there is some trickery involved because all the listeners that radio station would object?
Of course I was on the air for all people in Cambridge and Boston to hear.
Hatts of to professor I'm here after reading the book "for the love of physics" that's amazing
Does anyone know why the wine glass appears to be smoking while the sound is playing? I don't think it is dust, as I can see it in the beginning of the video and also further in while the strobe light is on as well.
Professor Lewin,
I've tried to use Faraday's law to come up with B_o= E_o / C by inserting a rectangular loop on x-z plane. However, my solution end up with extra minus sign, B_o= (-) E_o / C. Do you have extra note for checking my derivation?
tks,
+swh19 I refer to my lectures. I never check incorrect solutions.Sorry
Hi Sir, {Nice profile picture for your channel, by the way :) }
I have had always had trouble understanding electromagnetic waves, because they are so different from the waves we usually think of (like those on the surface of water, which require matter to propagate). After watching this video, I understand that an electromagnetic wave actually is E fields (and perpendicular B fields of course) travelling through space - please correct me if i'm wrong. What i find difficult to understand is how an E field (essentially a force field for charged particles) travels in space?
Your answers are all in my 8.02 lectures.
I knew this would be the wrong day to try out my new glass hearing aid. . . .
HI Professor, outstanding lecture as always, i'm a huge fan! regarding this one i was always told that takoma bridge fail is not an example of mechanical resonance but of an aeroelasticity and flutter problem. Whats your take about this? (thanks a lot)
use google.
Professor Lewin,
How do we measure such great distances as millions or even billions of light years ( 33:00 ). I can accept that if the galaxies are indeed that far away then we are looking into the past by observing them, but I am skeptical that we know they are so far away.
One more question, when you pranked the radio station ( 45:15 ), did it only effect your radio or radios in the area too? Either way it was hilarious!
Thank you
+Webb Telescope Google "cosmic distance ladder". My radio prank would only affect radios close to the lecture hall.
Very very interesting experiment. Your class is an art, professor. However, will the interference of the radio actually affect other audience around the city?
Only if the transmitter is powerful enough... I'm hoping that they were only transmitting with enough power to cover the lecture hall... Otherwise... Blame Harvard ;)
He was heard 5 miles away (he noted this in some reply to a comment).
The last demonstration was too cool.
sir in resonce condition ,amplitude goes on increasing with each oscillations ,right?If so why a wave with small amplitude in resonance with a glass could not break the the glass?
amplitude at resonance reaches a maximum as there is always damping on the system.
Can you please explain how do you get the derivative of phi with respective to time? All I know is about Fundamental Theorem of Calculus which states that the the derivative of an antiderivative F(x) = f(x)
Yun Heng Faraday's Law
the closed loop integral of E dot dl = - d(phi)/dt
phi is the magnetic flux going through an OPEN surface which is attached to the closed loop.
Is this of any help?
\\/\///////
Professor, if waves require a medium to travel through (water waves through water, sound through air etc), what's the medium for EM radiation (and light)?
no medium is required - www.google.com/search?safe=active&source=hp&ei=pnjQXLeNFu_45gLw47qABQ&q=michelson+morley&oq=michelcon+&gs_l=psy-ab.1.0.0i13l10.1906.4189..6173...0.0..0.118.984.9j3....2..0....1..gws-wiz.....0..0i131j0j0i10.mZhStc0ngQ4
I believe Professor Lewin does Caruso and other great singers a disservice. The glass is almost certainly a non-linear resonant system. This means its resonant frequency changes with the amplitude of its deformation. In the case of the glass, the resonant frequency decreases. As the amplitude of the deformation increases, the glass becomes increasingly detuned from the constant frequency signal, which no longer efficiently drives the oscillation. So of course, it has to be louder than necessary to cause breakage.
Not a professional, so a reply would be welcome.
Sir, i didn't find the notes of your lecture, can you provide me the link of the notes
Thank you for these brilliant lectures professor. I have a question here at about 24:15 where we are trying to predict the speed of light. From gauss’s law we followed flux of E = closed surface integral of E • dl = enclosed charge/u. Wont the charge enclosed be 0 since we have zero current? Also similarly for other 50% when we apply faraday’s law we need to compute flux of B = closed surface integral if B • dA which should be 0.
Given these scenarios I am having difficulties following how equations work out. Kindly guide me to understand what am I missing here.
>>>>> From gauss’s law we followed flux of E = closed surface integral of E • dl >>> this is not correct - watch my lectures on Gauss Law again.
Oh my mistake i wanted to say integral of E•dA.
After rewatching the lectures and going through my notes i understand that i confused between closed surface and open surface. Magnetic flux through closed surface is zero and not open surface. I also corrected my understanding of electric flux.
However I now have different question. Light is an EM wave so it has electric field. What I understand is that electric field originates from a charge but from what I have read so far photons do not have charge. So how does the electric field originate?
Edit: Oh I see you are going to cover this in next lecture so I will wait till that lecture. Thank you again for these lectures professor. These are really very helpful.
hello sir,
Am i right to think that a piano key produces one harmonic resonance when pressed and this tone isn't an interference of many harmonics?
Because a piano has well defined strings which do not change any factor of their own( l or v) . Plus for higher harmonics one has to go up on octaves. So one key, only one harmonic resonance and not superimposition of many harmonics as is the case with other instruments.
ohk sir. Got it...wud try it out with my piano and oscilloscope.Thanks a lottt for replying soo quick. Really appreciate it :)
I have become a huge fan of you through these lectures and Ur book"For the love of physics".
C'mon, record you piano string using your phone, cut thr first bit (about 0.1s might be enough for the middle C), and run the log-fourier transform on it. You'll see some nice stuff :)
in the above video, at 16: 44, it says that at an instant of time , E & B vector everywhere in that cross plane are same... As the E field oscillating only along X axis and B along Y axis, could you please clear the idea...
Watch the lecture in which I derive the EM plane wave radiation. That t4ells the whole story.
Hello and my deepest admiration for you Professor...I am incomplete in physics because there are so many things in this subject that should be learned very carefully combined with an appropriate imagination...I am in the 1st year for Electrical Engineering and I am interested in many new informations about physics...I have a question about one of these bringings... Is there ever meant The Tachyons Theory?...Does it appear properly to prove?...I found it as a hypothesis or as an unsolved postulate but I just wanted to know an opinion about it.
use google
@@lecturesbywalterlewin.they9259 I tried but it doesn't give too much information...That's ok...I referred to you in a inappropriate way and is just hypothesis about that information...So I apologise for disturbing and I appreciate too much your respond...Be strong the best!
5:30 Lewin would make a good beatmaker.
just wondering...when you were radio jamming did it only affect the radio in the room?
+John Lin Probably only a few hundred meters - definitely also outside the room
@@lecturesbywalterlewin.they9259 A few dozen Smoots outside the room at least
It occurs to me that perhaps Maxwell was the first of a new kind of physicist in that he _predicted_ the existence of a phenomenon (EM waves) from his equations. And only later was that phenomenon observed. Whereas, earlier physicists worked to explain what had been observed. E.g., the motion of planets, a compass needle moved by a current in a wire, etc. Nowadays a lot of physics is about finding the phenomenon (e.g., particles) that the theory predicts, but that wasn't the case before Maxwell. Does this make sense, or is my knowledge of science history flawed? Thanks
yes he predicted EM waves. At that time the speed of light was already known to high accuracy. Since his theory could predict the speed of EM waves, he was the first to conclude that light are EM waves.
I am still having trouble understanding how the electric and magnetic fields propagate. I understand that a fluctuating electric field at a point in a medium or vaccum can induce a magnetic field perpendicular to it at the same point. What I fail to understand is how they can influence another point in space near to that point.
Hello, the links in the description for the assignement and the solution don't work anymore and I really would like to see that proof for the speed of light. Where can I find them?
ocw.aprende.org/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/index.htm
@@lecturesbywalterlewin.they9259 Thank you, it was the link for 801 assignement, but following that link I found the assignement of 8.02.
Here are the links :
Problems: ocw.aprende.org/courses/physics/8-02-electricity-and-magnetism-spring-2002/assignments/ps9a.pdf
Solutions: ocw.aprende.org/courses/physics/8-02-electricity-and-magnetism-spring-2002/assignments/pss9.pdf
Incredible derivation of B=μεEc . Namaste sir , from India .
wonderful lecture professor :)
:)
They did a myth-buster video with a metal singer that was able to break the glass successfully.
I know
Sir,
Is range of antenna used in your lecture hall small?Only those radio in its range will receive your voice and all others from radio station , right sir?
students who lived 5 miles from the lecture hall could hear what I said.
Wow! 5 miles is pretty impressive!
Does any one know where can I find the homework assignments for this class? Thanks in advance!
playlist "8.02 Homework, Exams, Solutions & Notes"
I am confused with the way he derivates de function phiat min 26. Can somebody explain?
The web and another course I took said that the Tacoma Narrows bridge collapsed because of aeroelastic flutter. Isn't that a different phenomenon than resonance?
the resonace was driven by wind. Look at the video - The bridge is clearly oscillating in one (perhaps 2) of its normal modes.
Fun fact. If you turn rust (iron oxide) into dust and collect it between scotch tape.
You can record...the sound
Granted you need a magnetic field...to play it back.
So... what is the magnetic field?
Sir I have a Q
you demonstrated for string and musical instruments the air inside having harmonics. but how are different things supposed to have harmonics...they just vibrate to what we subject them to...😗
all objects have normal frequencies, all cavities too.
Lectures by Walter Lewin. They will make you ♥ Physics. ohhhho thank-you I never thought it that way...keep rolling sir
In to Resource freqency we give energy and the glass broken.
Was watching the video with headphones and the resonance frequency of the glass still seems to be tingling in my ears T_T.
:)
Your headphone had the quality of memorex
What is the energy that can push more air, the kinetic energy of a propeller or the resonant energy?
Assuming use the same electricity.
+Anonimousxz I do not understand the question
Lectures by Walter Lewin. They will make you ♥ Physics.
This resonant energy is the energy used que makes the hummingbird can fly, right?
The question is: What is the most effective energy to fly, the resonant or kinetic?
+Anonimousxz I do not understand what you mean by Resonant energy. Be more specific and what do you mean here by KE? KE of what?
Lectures by Walter Lewin. They will make you ♥ Physics.
Look hummingbirds and have your answer
Dear Professor, Would you explain about Laplace transform and Fourier Transform.
use Google and watch my 8.03 lecture + demos on Fourier series
sir are heat wave and infrared radiation same thing???
use google
it depends on defintions
all heat is IR radiation
dear professor thank you for solving all your students' queries Worldwide...:)
So does a wine glass have multiple resonant frequencies and the 488Hz are just one of those?
the glass = has many resonance frequencies - the lowest freq is the easiiest to break the glass.
@@lecturesbywalterlewin.they9259 But why is the fundamental the easiest to break glass? Because its also a resonant frequencies (the lowest). So why is the lowest freq the easiest?
When I watch this brilliant physicist, in the back of my mind I sometimes think. Who might be the opposite of this guy. This guy is the real thing, on the other hand, the media tries to convince us Bill Nye, the mechanical engineer, guy is the real scientist.
If I were attending MIT, I’d pop into his office and see what he thought of this global cooling, err umm, global warming, err umm, climate change issue.
difficult to read, bro. should've used grammarly.
What happens when you oscillate a quantum string to the point it breaks/snaps similar to the wine glass?
use google
Yea thats what I wanted to hear from a physics professor.... ALmost like michio kaku telling a 11 year old boy to go play in traffic.
Google has all the richness you could not even dream off. String Theory is not easy
It's unreasonable to expect that I can give you a satisfying answer in a few lines.
*Please don't be lazy USE GOOGLE*
I love to know how universe is working
When he does the integral for B dot dl, he appears to me to assume that B is in phase with E. But is that a fair assumption? Isn't that one of the things you have to prove? After all, a solution with a phase change would still a solution to the wave equation. So when he made both E and B cosines in phase, with synchronized t, he was seemingly assuming that without justification. Was he not?
The waves where E and B are in phase are consistant with Maxwell's eqs. There are also other solutions where they are not in phase. Thus my solutions are acceptable be it not complete. I suggest you watch my 8.03 lectures.
@@lecturesbywalterlewin.they9259 Thanks, I'm going to go through all of them. Is this reply from the real Professor Lewin? If so, thanks, legend! These are all really good.
Do you think you could do that to cancer cells??????
❤❤❤
Marconi was the first able to transmit radio signals.
I got an Glass today at work and put it into a holder with an other glas the one that i holded pulverized itself. I would like to know what that was :/
I would have to see a video
I only can tell what i saw: I was holding my Glas in my hand wanna put it into the holder it touched another glas just with a tip of itself and it shatters into its items. it was an new one out of an from me opened box. I cant even find something on Google over this...
But thanks for answering =)
If glass cools it can build up tension. We do a demo with a large (3 cm) drop of glass that we cool rapidly in water. That builds up a huge tension. I then scratch it with a small diamond and the glass beat explodes. However, drinking glasses are produced in a way that the tension is minimal and certainly an explosive shattering if you bang or scratch it would be out of the question. I suggest you try to reproduce the demo and video tape it.
10:15 of course it is possible for even a normal person to do this with minor training. It all depends on the wine glass material, which needs to be crystal. Crystal has a more ordered molecular pattern and is more prone to resonance. It's generally thinner and easier to break as well. Check out Mike Boyd's TH-cam channel to see him learn to do it. Science! th-cam.com/video/X6iJ0hPpGec/w-d-xo.html
Mr. Walter Lewin did you really jam the WEEI?
*yes I did*
Sir the assignments and solution links are broken !
core.csu.edu.cn/OcwWeb/Physics/8-02Electricity-and-MagnetismSpring2002/Assignments/index.htm
professor why aren't there any kappas and kappa m's in Faraday's law ?
+InventTwig dphi/dt is the magnetic flux through an open surface attached to a closed loop. No kappas!
+Lectures by Walter Lewin. They will make you ♥ Physics. ooh thank you professor :)
What makes you think they defy them?
how did he know that peculiar shape of the electromagnetic waves?
question unclear
My teacher says exactly same what u explained here he might have watched your videos
At 02:51 he says a dramatic story and screen color changes…
In this lecture you say that you think it's impossible to break a crystal glass using nothing but your voice. But it has been done in the past. An example of this is Mike Boyd. He spent a week trying to learn how to keep his voice at a loud and consistent frequency and trying to break crystal glasses until he broke one.
Here is a link to the video: th-cam.com/video/X6iJ0hPpGec/w-d-xo.html
I know that some people have done this.
Dear sir where is your lecture on speed of sound
plse search for it - I would also have to search
how did we modulate the 850Hz frequency?
how may minutes into the lecture?
41:08
you should have used google
en.wikipedia.org/wiki/Amplitude_modulation
I think, you can learn strong theory only if you do practical like these.
Interesting that these children are expected ( and probably it is true) to know integral calculus but the good dr. has to explain how a simple radio works, among other things. It seems to me that their mathematical acumen is disproportionate to their other talents. I think that is good.
students who are accepted by MIT must know integral calculus which they learn in their high schools. They have to do very well on their SAT. They do not have to know how a radio works.
I understand.
Using Faraday's Law, I'm getting E = - B c. Can't get rid of -ve sign!
Edit: by the way amazing ending!
Watch my 8.03 lectures
Sorry, I forgot to reply in happiness of finding the problem.
I chose area vector opposite to the the loop, that caused the minus sign.
I know it's a silly mistake, I do it on a regular basis 😅
SAY SORRY TO HARVARD SIR XDD
AMAZING DEMONSTRATION
Did you actually hijack that radio station or was your signal just strong enough to affect the radio in 26100😂
yes
Lectures by Walter Lewin. They will make you ♥ Physics. Must have been quite the demo😂
Sir can you please do something good for Indian viewers. Can all these lectures be translated into an hindi audio voice?