Dear Professor Thank you for your wonderful and extremely helpful video. I have a question to ask you. For diffraction, when the sin theta=1.5 lamda over D, why isn't the intensity maximum again? Wouldn't there be a construction again? Thank you so much.
@@lecturesbywalterlewin.they9259 Thank you for your response. However, in the intensity graph of diffraction, when sin theta=1.5 lamda over D, there is a smaller maximum intensity instead of destructive (0 intensity).
It seems to me that there is another argument why the number of lines has to be as large as possible, and therefore each line narrower, to conserve energy: the more lines, the smaller the surface blocking the light. It looks like the two faces of the same coin.
Is there a physical connection between: A) the circle of radius R formed by E-field vectors with δ phase difference and B) the angle θ that specifies the angle between rays of light? Or was the purpose of this circle to make the trigonometry easier to understand?
Thank you so much dear Professor Lewin. 1:05:32. if d/D=1/5, the 5th maximum grating will be killed, how about d=D? will it kill all the grating maximum except 0 order of course? thank you so much and have a great day!
Thank you professor especially for explaining the modulation in the diffraction pattern. In the last lecture, I observed similar modulation in the interference pattern that was demonstrated using only red light. I assumed the single slit diffraction pattern due to each of the slits caused this modulation like what happens in beat phenomenon and I felt excited to learn that my assumption was right. Also, I never felt comfortable with Huygen's principle for it never was the proper explanation of reality and I thought you would also explain what actually happens which gets Huygen's assumption correct in explaining this, since you quoted the author of the particular book in the beginning of the lecture. Can you please explain what actually happens here? This has been bugging me for long.
+Arunaday Gupta Huygen's principle is very powerful and is consistent with observations. en.wikipedia.org/wiki/Huygens-Fresnel_principle However, QM's approach is very different and fascinating; yet the results often do not differ from Huygen's Principle. I suggest you read about the double slit interference (QM) in the Feynman lectures.
+Lectures by Walter Lewin. They will make you ♥ Physics. Professor, I am comfortable with QM approach and I indeed find it very fascinating how the results don't seem to differ from Huygen's principle. However, for the classical approach I have found it very non-intuitive as to why should every point on a wavefront act as a secondary source of waves. Why do waves behave this way? And whenever it came to the explanation for single slit diffraction, I found it disturbing as to why should every point within the slit act as light sources as Huygen's principle described and not just for light but for diffraction of any other wave be it water wave or sound wave. But then again, in the link that you provided there was that argument on homogeneity of space which suddenly made me remember your lecture on Fourier Analysis where you showed that when you plucked at a particular point forming a square or triangular pulse, Nature doesn't differentiate between left and right and the disturbance travels in both directions to get reflected back again. Is this what happens to every point on the wavefront causing them to act as secondary sources, the resultant of which we obtain as a propagating wave?
+Arunaday Gupta Huygen's Principle is a model. Models in Physics are accepted as long as they work. They are no longer accepted as the observations contradict the models.
+Lectures by Walter Lewin. They will make you ♥ Physics. Thank you very much for answering my queries Prof. Walter Lewin! I should say that I owe a great deal of my understanding in undergrad physics to these extraordinary lectures of yours. :-)
light are photons. The energy, E, of each photon is hf. h is Planck's constant, f is the frequency. Einstein received the Nobel prize for his publication on the photo-electric effect in 1905. Thus if in our WRONG Newtonian world of thinking, there is NO such thing as 10 photons with the same frequency but with different amplitude as that would mean that the energy would differ. Use google if you want more.
Professor, I had a question if the silt width in a diffraction pattern is made half of its initial value what happens to the intensity of the central maxima?
I have question about 3D glass, the light pass through 3D glass is change wave length because filtering? In natual some color mixed together then reflected into our eyes some don't then it is black. Some object like fluorasent may emit light after absorbed. Can you take a photo of the gassoline vapour at gas station? (You may but need some manual adjusting). Another is about the Infared, one of it property is to bending to avoid some obstrucle. You may think about television remote control, that is one reason to use in telescope as higher frequency easier loss energy. But there is a limit of bending infared light.
Colored filters don’t change the wavelength of the light, it simply blocks the other wavelengths. If the filter wavelength isn’t present, the the filter blocks everything. If you look at a red light through a blue filter, you get nothing. It doesn’t turn the red light blue. Infra red from your remote doesn’t bend, it illuminates the walls like a flashlight would and the sensor in the tv can see that.
Sir in the case of single slit why did we get infinite number of destructive interference because when i look at that condition if we have N slits then we would get (N-1) minima so am confused here as there are single slit N = 1 hence N-1 means no destructive interference but not possible ?
Dear Mr. Walter Lewin.. Thank you for another wonderful and helpful lecture. I just have a question that I kindly wish you have an answer for it. My question is: when X-rays are diffracted by the atoms in crystal lattice, what causes the rays to be reflected? We all know that reflection happen when incident light with certain angle is reflected by the plane and the reflected light has the same angle. But what causes the X-rays to be reflected by the atoms?
at 1:07:7 demonstration with green laser there is a dark spacing b/w 0th order and 1st order maxima and so on........... but in graph intensity v/s sine we get continous envelope as if there is no dark spacing b/w 0th order and 1st order maxima.......i mean the envelope is continous then we get minima at 5th order so why there is dark spacing b/w 0th order and 1st order maxima ........in demonstration
I suggest you calculate the theoretical light intensity at a point in the middle between two maxima, and compare that with the intensity at the maxima.
what a lecture, invaluable contribution to the humankind
extremely helpful, thanks a lot professor.
this is also a good representation of heisenberg's uncertainty relationship
This man is just
"awesome"
When i get bored i watch your lectures
Dear Professor
Thank you for your wonderful and extremely helpful video.
I have a question to ask you. For diffraction, when the sin theta=1.5 lamda over D, why isn't the intensity maximum again? Wouldn't there be a construction again?
Thank you so much.
d*sin(theta) = 1.5 lambda => destructive interference
@@lecturesbywalterlewin.they9259 Thank you for your response. However, in the intensity graph of diffraction, when sin theta=1.5 lamda over D, there is a smaller maximum intensity instead of destructive (0 intensity).
My physics lab textbook has the formula you derived at 47:40 as I=I0cos^2(B)... I'm so confused...
My derivation is correct. Your book must have used a different notation. I cannot help you anymore. Use google
Lectures by Walter Lewin. They will make you ♥ Physics. Is the B in radians?
yes - watch at 50:00
All a misunderstanding! Thanks
You really taught us how to see the beauty behind the concepts!
It seems to me that there is another argument why the number of lines has to be as large as possible, and therefore each line narrower, to conserve energy: the more lines, the smaller the surface blocking the light. It looks like the two faces of the same coin.
Do we have infinite diffraction minimas or are they finite?
Kindly help.
The video was wonderful.
Ty prof. Walter.
look at the derivation of the patern and then judge for yourself. minima are ony *meaningful* if they have maxima on both sides
Is there a physical connection between:
A) the circle of radius R formed by E-field vectors with δ phase difference and
B) the angle θ that specifies the angle between rays of light?
Or was the purpose of this circle to make the trigonometry easier to understand?
I cannot add to the clarity of this lecture. I suggest you watch it again
Thank you so much dear Professor Lewin. 1:05:32. if d/D=1/5, the 5th maximum grating will be killed, how about d=D? will it kill all the grating maximum except 0 order of course? thank you so much and have a great day!
If d=D then there is no grating, so yes all you get is the original image.
Thank you professor especially for explaining the modulation in the diffraction pattern. In the last lecture, I observed similar modulation in the interference pattern that was demonstrated using only red light. I assumed the single slit diffraction pattern due to each of the slits caused this modulation like what happens in beat phenomenon and I felt excited to learn that my assumption was right. Also, I never felt comfortable with Huygen's principle for it never was the proper explanation of reality and I thought you would also explain what actually happens which gets Huygen's assumption correct in explaining this, since you quoted the author of the particular book in the beginning of the lecture. Can you please explain what actually happens here? This has been bugging me for long.
+Arunaday Gupta Huygen's principle is very powerful and is consistent with observations. en.wikipedia.org/wiki/Huygens-Fresnel_principle
However, QM's approach is very different and fascinating; yet the results often do not differ from Huygen's Principle. I suggest you read about the double slit interference (QM) in the Feynman lectures.
+Lectures by Walter Lewin. They will make you ♥ Physics. Professor, I am comfortable with QM approach and I indeed find it very fascinating how the results don't seem to differ from Huygen's principle.
However, for the classical approach I have found it very non-intuitive as to why should every point on a wavefront act as a secondary source of waves. Why do waves behave this way? And whenever it came to the explanation for single slit diffraction, I found it disturbing as to why should every point within the slit act as light sources as Huygen's principle described and not just for light but for diffraction of any other wave be it water wave or sound wave.
But then again, in the link that you provided there was that argument on homogeneity of space which suddenly made me remember your lecture on Fourier Analysis where you showed that when you plucked at a particular point forming a square or triangular pulse, Nature doesn't differentiate between left and right and the disturbance travels in both directions to get reflected back again. Is this what happens to every point on the wavefront causing them to act as secondary sources, the resultant of which we obtain as a propagating wave?
+Arunaday Gupta Huygen's Principle is a model. Models in Physics are accepted as long as they work. They are no longer accepted as the observations contradict the models.
+Lectures by Walter Lewin. They will make you ♥ Physics. Thank you very much for answering my queries Prof. Walter Lewin! I should say that I owe a great deal of my understanding in undergrad physics to these extraordinary lectures of yours. :-)
Dear professor Is there any reason why diffraction of waves of any type only depends upon wavelength but not amplitude of wave. thanks
light are photons. The energy, E, of each photon is hf. h is Planck's constant, f is the frequency. Einstein received the Nobel prize for his publication on the photo-electric effect in 1905. Thus if in our WRONG Newtonian world of thinking, there is NO such thing as 10 photons with the same frequency but with different amplitude as that would mean that the energy would differ. Use google if you want more.
Professor, I had a question if the silt width in a diffraction pattern is made half of its initial value what happens to the intensity of the central maxima?
Watch my lectures on diffraction
I have question about 3D glass, the light pass through 3D glass is change wave length because filtering? In natual some color mixed together then reflected into our eyes some don't then it is black. Some object like fluorasent may emit light after absorbed. Can you take a photo of the gassoline vapour at gas station? (You may but need some manual adjusting). Another is about the Infared, one of it property is to bending to avoid some obstrucle. You may think about television remote control, that is one reason to use in telescope as higher frequency easier loss energy. But there is a limit of bending infared light.
use google
No I know the answer, I just try to share some. May be we can more enjoy the lesson.
Colored filters don’t change the wavelength of the light, it simply blocks the other wavelengths. If the filter wavelength isn’t present, the the filter blocks everything. If you look at a red light through a blue filter, you get nothing. It doesn’t turn the red light blue. Infra red from your remote doesn’t bend, it illuminates the walls like a flashlight would and the sensor in the tv can see that.
Sir in the case of single slit why did we get infinite number of destructive interference because when i look at that condition if we have N slits then we would get (N-1) minima so am confused here as there are single slit N = 1 hence N-1 means no destructive interference but not possible ?
sir how did you calculated those no of lines N = 1600 that are being used up when we shine laser beam on grating having 13000 lines/inch.
sir understood we just need to know how many lines can be fit in 1mm i.e. 526 lines and so in 3mm close to 1600 lines can be there :)
Dear Mr. Walter Lewin..
Thank you for another wonderful and helpful lecture. I just have a question that I kindly wish you have an answer for it.
My question is: when X-rays are diffracted by the atoms in crystal lattice, what causes the rays to be reflected? We all know that reflection happen when incident light with certain angle is reflected by the plane and the reflected light has the same angle. But what causes the X-rays to be reflected by the atoms?
www.xtal.iqfr.csic.es/Cristalografia/parte_06-en.html
Lectures by Walter Lewin. They will make you ♥ Physics. Thank you for your time Sir. I got an A today. Much appreciated!
When there would be captions for the lecture ?
Sahil Goyal there's few more years for auto-sub to Android, Pixel 4 is the only one in the mean time.
Name the Scientist who discovered analysis of spectral line can be possible based on, if Iron is present in hot atmosphere of star ?
at 1:07:7 demonstration with green laser there is a dark spacing b/w 0th order and 1st order maxima and so on........... but in graph intensity v/s sine we get continous envelope as if there is no dark spacing b/w 0th order and 1st order maxima.......i mean the envelope is continous then we get minima at 5th order so why there is dark spacing b/w 0th order and 1st order maxima ........in demonstration
I suggest you calculate the theoretical light intensity at a point in the middle between two maxima, and compare that with the intensity at the maxima.
Sir I didn't understand what u said to calculate the I max which formula I heard it like 'lo pi tau'
how many minutes into the lecture?
He's talking about L'Hospital's Rule.
10:57 sir what is lo pi tau
I watched at 10:57, there is no pi and no tau
Sir is it the L hospital rule ...
Cause I searched in internet for Lim of 0/0
I love you Walter
wrr