Blackbody Definition and 181 Threads

Homework Statement By direct calculation, derive and expression for the wavelength λ(max) at which blackbody radiation intensity is a maximum [b]2. Homework Equations Planck's law for the intensity distribution of blackbody radiation as a function of wavelength λ and the blackbody...

I don't see how this follows.

Hello. I am trying to study "Introduction to Cosmology" by Barbara Ryden, but I am stuck with an equation from chapter two, and I have no idea how to figure out this. If you can suggest me a reading material or can explain the equation to me, that would be wonderful. It is page 20 of the...

Homework Statement The following is from a book: "Terrestrial radiation, T=255 K. Emitted flux ≈ 240 W m-2. Energy density for cavity radiation ≈ 3x10-6 J m-3. Entropy for cavity radiation ≈ 1.7x10-8 J K-1 m-3." I can't understand how they have calculated the Entropy.The Attempt at a...

Homework Statement A blackbody is radiating at a temperature of 2.50 x 103 K. a) What is the total energy density of the radiation? b) What fraction of the energy is emitted in the interval between 1.00 and 1.05 eV? c) What fraction is emitted between 10.00 and 10.05 eV? Homework...

My question is about using an IR thermometer for measuring the temprature of a blackbody that emitts a spectrum that peaks somewhere in the visible region. I think since these kind of thermometers measures the amount of infrared radiation emitted by the object, they can only determine the...

Is the sun a passive or active blackbody? Thanks

Homework Statement (a)The cosmic microwave background fits the blackbody radiation spectrum well with a temperature of 2.7 K and a corresponding peak wavelength at 1.9nm. Applying the relationship between the radiant emittance, i.e. the total power emitted per unit area, and the photon energy...

# of photons in a mode (in a blackbody) I've been going over a proof again concerning the thermal average number of photons in a mode of a cubical blackbody of length 'L' at equilibrium with a reservoir of temperature 'tau' (has a small hole in it, etc. etc. etc.) The logic went as usual...

Homework Statement Imagine you are trying to detect a Jupiter-like planet located 7.5E11 m from a Sun-like star. At what wavelength is the peak of the planet's Planck blackbody intensity function (assume the planet is a perfect blackbody)? Radius of Planet r = 7E7 m Radius of Star R =...

"Theory" question -- Blackbody Radiation and Light I am trying to understand the discussion about blackbody radiation in my Modern Physics textbook. (I'll quote it, but it can be found http://phy240.ahepl.org/Chp3-QT-of-Light-Serway.pdf" , page 5 document numbering, 69 textbook numbering)...

Let's say there's a perfect blackbody inside a box (at room temperature) composed of material such that only x-rays are able to enter and leave. If the absorption and emission of the x-rays weren't the same, the box would heat up above room temperature, and this would contradict thermodynamics...

Homework Statement My question is, why, when changing the variable from "v" to "lambda", does the d\lambda need to be included? Why can't a simple substitution c = v * lambda do the trick?

I saw a claim today that without the greenhouse effect, Earth's surface would be on average at a chilling -18°C (note: this is not a climate change thread). I set about trying to reproduce this result, so at first I assumed that Earth was a perfect blackbody, and that in order to be in...

I've seen the cavity resonator model but no one has been able to explain to me what the underlying physical mechanism is that generates the blackbody radiation continuum. Is there some intuitive explanation or is it deeply rooted in quantum mechanics? An explanation I've heard is that it's...

It seems it is predicted by both classical and quantum physics. Why is it predicted in the first place? Is it purely a mathematical reasoning, or is there some qualitative reason why it must exist? In other words, why would some philosopher/physicist hundreds of years ago say to himself, "I...

physics books on the topic of blackbody radiation say that any given object when heated will emit a continuous electromagnetic radiation which depends only on temperature. Planck's distribution based on discretization of energy states accurately describes this phenomenon. But is this true? If...

1)Is it possible to concentrate infrared radiation from a blackbody with a lens? 2)Should a lens be at different temperature from a blackbody?

If I may dare to ask the question: WHY are bodies absorbing and radiating heat in same proportion? I can't find the answer anywhere on the internet. And why are bodies radiating heat in the first place? And why whole spectrum of wavelengths?

I was thinking about this the other day and I wanted some other input on the matter. Cups of boiling water (I was thinking about coffee) give off gobs of IR radiation at both near and mid wavelengths. Could I think of a coffee mug as an approximate black body for IR radiation? The insulation of...

Hi all, I have 2 questions related to the blackbody spectrum. 1 - If a blackbody emits (and absorbs) energy at all wavelengths equally, why does the spectrum look the way it does (i.e. why does it peak in intensity at a given wavelength?) 2 - The fact that the cosmic background radiation...

Hello all, Does anybody have an idea why the solar spectrum, as measured above the Earth's atmosphere, has such bad agreement with the blackbody curve? I would think that any deviations such as sunspots would be averaged out because of the distance, and that in general (if any deviation)...

According to the blackbody effect, can something be so hot that it emits no visible light? I say this because the more heated an object is, the more it moves away from the visible light spectrum, does that apply until there is no light at all?

Homework Statement By what factor does the radiated energy increase when a blackbody changes temperatures from 100K to 1000K a) 100 b) 6600 c) 1 x 10^ 4 <--- marked as the correct answer on the key. d) 5.7 x 10^4 e) 1 x 10^6 Homework Equations 1) f(peak) = 5.88x10^10*T 2) E =...

Good Day, I was wondering whether anyone has a reference or can point me in the right direction for a mathematical derivation of how the photons in blackbody radiation (for solids) are generated from thermal motion. Regards Max

An evacuated container with volume V and at a temperature T contains black body radiation with an energy density equal to 4T4/c S(T,V)=16VT3/3c The container is placed in thermal contact with a heat bath at temperature Tr. If the heat capacity of the cavity material itself is...

If light is quantized, and is given out in packets, why are the EM wave spectrum and the black body spectrum continuous? I am very confused, can someone offer some explanation? Any input is greatly appreciated.

I'm reading from an introductory text on quantum physics, and came across this sentence: It's the second sentence that I don't understand: how can the energy in the EM field be responsible for the ability of a hollow cavity to absorb heat?

Homework Statement Problem 2.11 of Liboff's Introductory Quantum Mechanics, 1st edition Suppose that you are inside a blackbody radiation cavity which is at temperature T. Your job is to measure the energy in the radiation field in the frequency interval 10^{14} to 89 \times 10^{14}...

Hi All, I'm reading about blackbody radiation and emissivity and I came upon the following statement "Imagine looking into a small opening of a deep cave. In the visible wavelengths, the opening looks black because the light that enters the cave is not easily reflected back out. However...

Homework Statement b) Two stars, both of which behave like black bodies, radiate the same total energy per second. The cooler star has a surface temperature, T, and 3.0 times the diameter of the hotter star. i) What is the temperature of the hotter star in terms of T? ii) What is the ratio of...

Homework Statement Derive an expression for the temperature of an ideal blackbody so that its radiated light at the peak intensity wavelength has exactly enough energy to excite the ground state to fourth excited state. Homework Equations I = σ*T4 λm*T = 2.9 * 10-3 m * K E = hf = hc/λ...

Blackbody radiation problem! Homework Statement The average person has 1.4 m^2 of skin at a skin temperature of roughly 306 K. Consider the average person to be an ideal radiator standing in a room at a temperature of 293 K. a.) Calculate the energy per second radiated by the average person...

The maximum wavelength for blackboby radiation is .29/Temperature. Is the average wavelenght 1.84 times the maximum for all temperatures?

Hello, I got a question about this famous graph of the spectrum given by a heated body, showing the classical line (which goes up) and Planck's line (which gives the hill shape). How is this line continuous? Let's say my body is a lump of hydrogen, the only points on the graph should be the...

I know the CMBR temperature was approximately predicted by Alpher ,Herman and Gamow around 1948, but I can't locate a source specifying when and how the blackbody form of the CMBR was predicted. Does anybody have this information? thanks

Homework Statement Starting with the Planck distribution: R(\lambda,T) = \frac{c}{4} \frac{8 \pi}{\lambda^4} (\frac{hc}{\lambda})(\frac{1}{e^{hc/(\lambda kT)}-1}) Derive the blackbody Stefan-Boltzmann law (ie total flux is proportional to T4) by integrating the...

Homework Statement Starting with the Planck distribution R(\lambda,T) for blackbody radiation. (a) Derive the blackbody Stefan-Boltzmann law (ie total flux is proportional to T4) by integrating the above expression over all wavelengths. Thus show that R(T) =...

Ive heard a black body described as 'a body which absorbs all the radiation that falls upon it'. This seems to me to contradict the idea that a black body emits exactly as well as it absorbs light. I can understand that if you shine light matching a blackbody curve (at a given temperature) on...

You can know the temperature of a star by fitting a black body spectrum. BUt what if the star is moving with some radial velocity v? I worked out that: I(\lambda_0,T)=\frac{8\pi h c}{\lambda_0^5}\frac{1}{e^{\frac{hc}{\lambda_0kT}}-1}...

Homework Statement a 100W beam of light is shone onto a blackbody of mass 2e-3 kg for 10e4 seconds. The blackbody is intially at rest in a frictionless space a) Compute the total energy and momentum absorbed by the blackbody from the light beam b) calculate the blackbody's velocity at the...

A well-established physical law describes the transfer of heat between two objects, but some physicists have long predicted that the law should break down when the objects are very close together. Scientists had never been able to confirm, or measure, this breakdown in practice. For the first...

I've read that the phenomenon of black-body radiation was one of the key factors in the creation of quantum mechanics. So I want to learn about it...;-) First of all I don't understand why the the temperature of the black body increases when it absorbs energy from photons. Why can't the...

Hi. I know this is a pretty basic principle, however I'm fairly new to the subject and was wondering if anyone is able to give a brief 'layman' explanation of why, as Planck's law states, at lower wavelengths the blackbody radiation falls to zero rather than continuing to climb as stated in the...

Homework Statement This is the integration i have to solve I=\int x^{2}In(1-exp(-ax))dx integration is from zero to infinity The Attempt at a Solution I know that it should be solved with integration by parts so u=In(1-exp(-ax)) du=[a exp(-ax)] / [1-exp(-ax)] dv=x^{2}dx...

http://hyperphysics.phy-astr.gsu.edu/hbase/mod6.html#c4 This link shows the general plot of energy emitted by a blackbody against frequency. My two questions regarding this plot are: 1. Is the frequency in the plot the frequency of EM radiation emitted by the blackbody? 2. Why does the...

any electron will be emitted if i use a black body as a metal target in photoelectric effect experimant and why??

Hi, having a bit of trouble with a basic question on thermal radiation. If you take a slab of material that has the characteristics of a blackbody and heat it to temperature where its only emitting in the IR, then its temperature will slowly decrease as the heat is rejected (assuming no...

Homework Statement In case of Cavity Radiation(Blackbody radiation) let \rho_{T}(\nu)d\nu denote the energy density of radiation having frequency in the interval \nu and \nu + d\nu. Then we need to show that \frac{\int_{0}^{\lambda_{max}} \rho_{T}(\nu)d\nu}{\int_{0}^{\infty}...

Homework Statement Suppose that a blackbody spectrum is specified by Spectral Radiancy R_{T} (\nu) d\nu and Energy Density \rho_{T} (\nu) d\nu then show that R_{T} (\nu) d\nu = \frac {c}{4}\cdot \rho_{T} (\nu) d\nu Homework Equations \rho_{T} (\nu) d\nu = \frac{8 \pi h \nu^{3}...