This is one of those those great but largely undiscovered nuggets that not only explains the subject of blackbody radiation in detail but also, importantly, the historical context of the research, the questions being asked about the relation between frequency and temperature, and the steps that led to a solution.
Planck's approach was to analyze the entropy of blackbody radiation as a function of energy. To make both high-frequency and low-frequency data consistent with the Second Law of Thermodynamics, he included an additional "guess" term proportional to the frequency. Planck's application of Boltzmann's Statistical Mechanics led to his conclusion that the material of the walls emit and absorb radiation in discrete quanta. A paper titled "Planck’s Route to the Black Body Radiation Formula and Quantization" by Michael Fowler (7/25/08) gives a nice discussion.
Thank you so much for including the history as well, I rarely find such high level lectures incorporating information in an interesting narrative! Subscribed!
Outstanding explanation sir,u really explained in such a great way that made this most confused topic very interesting and very easy .I am ever grateful to you.thankyou so much sir,for explaining this topic in a clear and best way .keep doing more videos like this ,it will be very very helpful to us.All the best sir,u should reach heights❤
very nice video. How the Planck ypothesis explains the Ultraviolet Catastrophe ? I mean why the fact that emitted radiation has energy E= nhf, leads us to predict the actual distribution of the black body radiation at all wavelengths? Why most of the emitted energy is located at a small area of the spectrum?
With regards to Ultraviolet catastrophe - IF YOU PUT THE FORMULA ASIDE, THEN WHAT IS THE INTUITIVE reason BEHIND the math so one can SEE the intensity going down on higher frequencies, I mean conceptually?
Very clear explanation. But why are the curves shown smooth? Is it that there are so many frequencies thaat they appear smooth but if we had better definition we would see little spaces between the points?
yea that's exactly it, we just use a smooth curve to represent it since there's so many different possibilities for frequency (a lot, but not infinite). If you zoomed in on the x-axis you would see discrete quantities
Planck constant is energy in one photon. Multiply this by number of photons per second and you get the energy of a radiation based on frequency or color of the radiation.
@@PhysicsOMG Thank you so much. Your answer is very interesting my dear professor. someone else said the following? Planck's constant is, indeed, the smallest constant used in physics, which is reflective of the quantum scale. However, it is just a scale and not a physical quantity. Hope that clarifies it. please could you give your opinion on this ?
Please tell me how you do the whiteboard thing its the exact setuo as Joel Speranza and hes keeping the secret safe. My final physics exam for 50% is tomorrow morning but this is the most important thing right now.
lol it's pretty easy, I set up a camera in front of me, I sit behind the board and write. In the original video, all the writing looks backwards but when you mirror the image it comes out right. You can tell because I'm right handed but it looks like I'm writing with my left hand in the videos
@@PhysicsOMG thank you i thought this was the case. Physics was easiest exam ever although I forgot a few formulas and wrote wrong ones down lol it happens
Thanks for the video. I am trying hard to understand this topic. To me, E=nhf just means that energy is a function of frequency and does not imply discreteness since presumably f can vary. Or is the point that for a *given frequency* energy can only be positive integer multiples of hf? How is frequency allowed to vary? Is frequency also quantised somehow?
Frequency is continuous and can be any value you want. But for a given frequency, the light is actually emitted in little chunks that are a multiple of Planck's constant instead of one big wave. It's not the value of the energy itself, but the wave packets that carry away the energy that are quantized.
@@PhysicsOMG Thank you for that clarification. I really like your explanations. I am still a bit confused though. If energy is quantised, then it stands to reason that the energy that you put into your black box to heat it up is also quantised. And therefore only certain frequencies will ever be input or emitted. Where does the continuous spectrum of frequency come from? There's something missing from this picture, at least to me :)
hey that was a very nice video. Im a high school physics student and some questions I have are: -why do the intensities of wavelengths lower than the peak value decrease so quickly as compared to the curve for the wavelengths higher than the peak value? -does the black body radiation curve mean that it cannot be applied to objects that are not good absorbers of radiation, e.g. plastic? Thank you if you answer these questions
Thank you, I'm glad it helped! For your first question, remember that the smaller wavelengths (which drop off quickly) correspond to higher energy photons. If you have an object at a certain temperature, there is only so much energy that can be radiated (no UV catastrophe). So there can't be very many of these high energy photons because statistically it is more likely for the low energy ones to be given off. That's why the low energy end of the spectrum gradually trails off but the high energy one drops off quickly - the probability of high energy photons becomes basically 0 beyond that peak. There is a really good minutephysics video that explains why its mostly lower energy photons that get emitted: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-i1TVZIBj7UA.html For the second question: in real life the only things we see that actually behave like true blackbodies are ones we make (like the example of an oven with a hole punched in it), or stars. Everything else will sort of follow that curve but will only have a fraction of the ideal emission seen in a blackbody curve. So yes, something that is a poor emitter will not have an emission curve that looks like a perfect blackbody curve.
@@PhysicsOMG The bit I struggle with is (as Fairboy says) - h fixes the curve, but why? I wish someone could explain what is happening as we move along the curve, why does it come back down?
in 03:59 he says maximum or the peak wave lenght but if the wavelenght is plotted along x axis shouldn't the peak wavelenght be at infinity (according to the graph)? or should it be peak intensity ?
By peak wavelength we mean the wavelength that corresponds to the peak in the graph. That shows us the most common wavelength of photon that is emitted by the blackbody.
yea, basically if that model was correct then the object would emit infinite energy at smaller wavelengths and do all sorts of other insane stuff they knew must be wrong
Maybe infinite in this riddle makes the black⚫ night sky☁ turn blue in the daytime. If not, then it's something to imagine a dazzling sun ☀️ against a black⚫ background of the night 🌃sky which would behave like the black body. Power of infinity.
I'm not German so I'm no authority on it but I think it's plahnk. I just say it the same way my physics teacher always said it when I was in high school.
