Blackbody Radiation Part 1 - Experimental Observations: Stefan Law, Wiens Displacement Law

Blackbody radiation refers to the electromagnetic radiation emitted by an object at a given temperature. A blackbody is an idealized object that absorbs all radiation that falls on it and emits radiation at all wavelengths.
Stefan's law, states that the total amount of radiation emitted by a blackbody per unit time and unit surface area is proportional to the fourth power of its absolute temperature.
Wien's displacement law, relates the wavelength at which the spectral radiance of a blackbody is at a maximum to its temperature. Specifically, the product of the wavelength of maximum emission and the temperature of the blackbody is a constant: λ_maxT = b, where b is a proportionality constant.
In this video I discuss all the above, as well as various experimental observations.
00:00 Introduction
11:39 Experimental Observations
13:56 Stefan Boltzman Law
17:09 Wien's Displacement Law
20:42 Conclusions
𓏬𓏬𓏬𓏬𓏬𓏬𓏬𓏬𓏬𓏬𓏬𓏬MY NOTES - GDRIVE𓏬𓏬𓏬𓏬𓏬𓏬𓏬𓏬𓏬𓏬𓏬𓏬
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[@FortheLoveofPhysics]

1. Blackbody Observations - kzbin.info/www/bejne/fIPHY2t5gduAh68 2. Rayleigh Jeans Law - kzbin.info/www/bejne/oXndZ62YedacnLM 3. Planck Energy Distribution - kzbin.info/www/bejne/qnK9in6EgNCrqZY 4. Summary - kzbin.info/www/bejne/gYObhKCQast6f8k

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[@user-sz5dt9ih7f]

I would tell anyone who wants to study thermodynamics that they watch your lectures first. You presentation is just brilliant!!! For instance, I did not even think about why physicists thought of using a hollow sphere. Your insight that a flat surface would reflect some of the radiation which then would not be able to be recaptured is a great one! I watched countless videos on this very subject and was never satisfied.

[@jasnoor8-d-155]

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[@ankushabhat1599]

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[@khushbusahani9101]

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[@bpperbpper7750]

This is brilliant. I'm so hungry for more lectures. Thank you very much for your effort!

[@samraawan841]

great lecture. But I'm confused is it Lambda minimum or lambda maximum associated with neu maximum in your derivation. Please help

[@rohankanu9880]

Yeah it's lemda minimum

[@wahydgold]

@@rohankanu9880 because wavelength and frequency are inversely related.

[@appannasidagam8564]

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Very precise and impressive lecture .... thoroughly understand black body radiation.

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congratulation sir for 100k subscribers.

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[@kainturaji3689]

Wonderful sir ❤️ Sir one request can you please make it one video at a week so our learning will be more disciplined and quite regular. I know you have to manage other things as well but if possible please consider this also.

[@ekta-jangra]

Very nice explanation Sir 👏 Thanku Sir😊

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❤ excellent, excellent, excellent.... 🎉

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[@user-fm2fq6qx8l]

Thankuu sir😊

[@Rainbowcolours09]

Nice Session Sir...just wondering your classes 🎉...and now becouse of u l came to know the basics...😂

[@fractalnomics]

Snow and white paint have similar emissivities of near 0.9. Does this make them near blackbodies?

[@harry-ho9ti]

Kindly upload at least two lecture in a week

[@malavikap7433]

Sir, I have a doubt. If the blue chalk is absorbing all the other wavelengths what is happening to the electrons of the atoms of the chalk that are absorbing all the incident light? That incident light is probably not enough to excite the electrons into their higher states. Please explain. Thanks.

[@thusithawickramanayaka4493]

Dear Sir, Can we have the remaining topics in QM also ....? Thanks for your superb series of lectures..

[@abdurrauf7525]

Sir, I also wonder whether there were experimental observations and scientists were trying to explain the spectrum. Or theory and experiment were going side by side to derive a function proposed by Gustav Kirchhoff (the radiation emitted from a black body within a given wavelength interval is a universal function depending only on the temperature of the body) about black body radiation.

[@Awakeknowledge]

i like much sir your english communications skills.

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The speaker (I can't find his name) must have had wonderful teachers. He speaks very well, has excellent handwriting, and can draw lines and circles with great skill.

[@Kneegrowww_911]

Dibyajyoti Das...found it in the description

[@ronitkumar4619]

Spectral Energy Density - Amount of energy per unit time per unit surface area that is being emitted by the black body cavity for a given range of frequency of an EM

[@sayantanpaul1655]

Sir if a perfect black body emits thermal radiation in visible spectrum range how can it be a black body to our eyes ...

[@sanjanayadav9765]

Sir the graph of spectral density versus frequency graph not start from origin why you draw it from origin?

[@alkasoni4688]

Sir i have query only why black body choosed for the experiment .why only thermal radiations.

[@sushmamishra9268]

Next lecture please 🙏

[@impresent2005]

sir, I have a doubt...... sir as Vmax is directly proportional to temp. and when we do c/lambda.....so, lambda must be minimum but apne maximum likha hai????

[@faisayousufzai9057]

Sir why wavelength maximum with maximum frequency?

[@alishair6444]

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[@sanjanayadav9765]

Sir why we use metal while designing black body

[@anandchaurasiya2668]

Sir need lecture on polarization of light such as circular ,eliptical ....

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BEST

[@shyam5604]

Lambda max or lambda min ? at 18 min

[@user-ne4gc1mg5e]

About the quantum of light 1- In the 19th century, much attention was paid to the study of the thermal properties of various objects. The idealized model that was considered was the Black Body. (Max von Laue called the black body the “Kirchhoff vacuum.” It was also called the “ultraviolet catastrophe”; the first signs of the “vacuum catastrophe”) 2- In 1900, Max Planck solved the “black body” problem by discovering the “quantum of action of light - h”. Particle (h) is not a hot particle emitted by stars. Particle (h) came from the vacuum, from the cosmic vacuum. 3- Einstein's second postulate states: In a vacuum, light propagates at a constant speed (c), which does not depend on the speed and radiation of the source or observer. 4. According to SRT, a quantum of light is not a solid particle. 5- According to quantum physics, a quantum of light has its own internal “spin” (linear or angular). 6- Light is an independent and free quantum particle. Its movement does not depend on the speed of the source or the observer. The actions of light do not depend on the opinions of physicists. # "All these fifty years of conscious brooding have brought me no nearer to the answer to the question "What are light quanta?". Nowadays every Tom, Dick, and Harry thinks he knows it, but he is mistaken." /Albert Einstein/

[@gok_dogan]

Professor I wonder that Can a free electron (in vacuum) absorb photon ? Likewise is it possible for an electron (it isn't in an orbit of an atom ) to emit photon ?

[@suneecat]

Of course, both are possible. The question is, under what conditions is each behaviour likely to occur.

[@harry-ho9ti]

Excellent explanation as compared to others❤. Hope ur health is OK sir.

[@FortheLoveofPhysics]

I am fine now. Thanks :)

[@dr.saurabhkunj5423]

@@FortheLoveofPhysics Good to listen that

[@mrslave41]

<a href="#" class="seekto" data-time="794">13:14</a> Can you explain how this graph was obtained?

[@FortheLoveofPhysics]

It's an experimental observation, of radiation Power (for a fixed frequency width) v/s frequency

[@abhijitchatterjee3129]

Your answer to the following please: Suppose there is a cave where we can't see anything inside. There is an opening of the cave, and from outside if we look through, nothing can be seen. Because it can act as a black body. Now, can I interpret like, some may be seen within, in summer rather than winter. Because, in summer, the temp of the cave ( black body) remains high enough and hence the emitted thermal radiation would be more and of higher energy and may fall in the visible region.

[@homemobile8362]

<a href="#" class="seekto" data-time="734">12:14</a> ;I have small doubt on x axis of this graph sir ,i saw many graphs labeled it as wavelength 🤔not frequency, why is it? Wavelength is inversely proportional to frequency ?

[@FortheLoveofPhysics]

Yes, wavelength and frequency are inversely proportional. If you go through the literature, you vl find many books with frequency on the x axis and many others with wavelength. Both are OK. I chose frequency, as in later lectures my calculations will be very much based on frequency

[@homemobile8362]

Okay thank u sir❤❤❤

[@wisdomkeytraining700]

Sir, shouldn't be graph between power or intensity and wavelength of radiation??

[@seekingrafael5630]

I think so too

[@vipinpnair]

I see emissivity factor is also considered for thermal calculations. But this is missing here in these lecture series . Please include a reason why emissivity changes with material, even though black body radiation is independent of material.

[@mysterious5678]

I think it's only about Blackbody. Hence, sir didn't include emissivity.

[@suneecat]

At <a href="#" class="seekto" data-time="1063">17:43</a> you say "... for another body ... ". What you really mean to say is "... for another temperature ...". That would be more clear. But nonetheless, a great lecture. Very informative and very well done. Thank you.

[@motif123456]

It would be nice if you could derive plank's spectral irradiance formula in your subsequent video

[@FortheLoveofPhysics]

Will do

[@cantantephoto8696]

21.40 “if a charged particle like an electron is vibrating (due to higher energy/heat) then it emits an electromagnetic wave” Sounds obvious if the penny has dropped. Why hasn’t any book I’ve read explained it so simply before? Thank You.

[@rishidevpandey1618]

Sir where u have taken the lamda max there will be lamda min

[@prajwalshrestha4210]

lambda max corresponds to wavelength with max energy density

[@abdurrauf7525]

Sir, is the name black body appropriate at all temperatures? Or only at room temperature. Sir, kindly also discuss Wein's approximation in the upcoming lectures. Thanks

[@FortheLoveofPhysics]

The name may be more appropriate for room temperature, as it is supposed to appear black by virtue of being a perfect absorber. But the name is now stuck. So even the Sun is a non-ideal blackbody, as it only radiates out acc to the blackbody spectrum

[@abdurrauf7525]

@@FortheLoveofPhysics , thank you sir. Sir, I do not understand why the black body needs to be in thermal equilibrium with the environment. Because on one side we are saying that the black body needs to be in thermal equilibrium with the environment and on the other side we have a spectrum of radiation at different temperatures (i.e. we are increasing the temperature of black body).

[@prestigious786]

​@@abdurrauf7525one curve is obtained at a particular temperature so equilibrium should be there. To record the second graph, we first change the temperature to desired value then maintain it n take measurements.

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<a href="#" class="seekto" data-time="300">5:00</a>

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[@amritsagarkar7899]

Sir how to take notes from your lectures. Plz make a video on that . If you can't make the video the plz don't change the way teach, it would be hard and time consuming for me to take notes but I will try to manage that. Plz keep this teaching method!!

[@brantbarker181]

golden foil in theory can strip a positive from the particle and not render it less harmful

[@gyaani6993]

Part 2...

[@maryamriaz]

charge particle emit radiation

[@anitsharma5582]

bhot accha pdate ho aap .... hindi m bhi bola kro thoda

[@profhalimboutayeb]

Nice video. A simulation of blackbody radiation using Maxwell's equations (without the concept of energy quantization): kzbin.info/www/bejne/m2jbnn-viNGCi8k Both Planck's law and Wien's law are retrieved. The theory we use is inspired by Wien's work. It is not published yet.