Black Body Radiation (1 Viewer)

[taeyang]

Can someone PLEASE help me with Black Body Radiation. It has been bugging me since day one. I mean I get the idea, somewhat, and the good ol'e Jacaranda furnace analogy, but I just don't understand the GRAPH of classical vs quantum physics, why does it bend down at the end? Is it because when there is too much energy in the black body cavity, it will emit it in discreet quanta? and that is why as the wavelength decreases the intensity decreases? because it releases the high energy within? gahh, ahjhmajhfiogidfjo

And how does this lead to Einstein? Is it that he described the quanta of energy being "photons" and that they emit after given enough energy? ok thanks guys for the help, trials tomorrow so gotta get some sleep thanks thanks thanks.

 

[michaeljennings]

Can someone PLEASE help me with Black Body Radiation. It has been bugging me since day one. I mean I get the idea, somewhat, and the good ol'e Jacaranda furnace analogy, but I just don't understand the GRAPH of classical vs quantum physics, why does it bend down at the end? Is it because when there is too much energy in the black body cavity, it will emit it in discreet quanta? and that is why as the wavelength decreases the intensity decreases? because it releases the high energy within? gahh, ahjhmajhfiogidfjo

And how does this lead to Einstein? Is it that he described the quanta of energy being "photons" and that they emit after given enough energy? ok thanks guys for the help, trials tomorrow so gotta get some sleep thanks thanks thanks.

Do you go to baulkham hills lol?

 

[miniwaybzz]

why does it bend down at the end? Is it because when there is too much energy in the black body cavity, it will emit it in discreet quanta? and that is why as the wavelength decreases the intensity decreases? because it releases the high energy within? .

OMG. I dont get that either!!
Can someone please explain it??

 

[kazza9]

The reson it must curve down is because if it keeps increasing at an infinite rate it won't comply with the law of conservation of energy

 

[Fizzy_Cyst]

OMG. I dont get that either!!
Can someone please explain it??

The BBR curve is basically a probability curve showing the probability that an electron will undergo a specific energy transition. The peak on the BBR curve corresponds to the electron energy level transitions which are most probable at the given temperature.

The reason why it bends down drastically at wavelengths lower than the peak is as wavelengths lower than peak wavelength corresponds to an electron transition which releases more energy than the average energy and this requires more thermal energy than the average thermal energy of the blackbody, hence is more unlikely to occur the further away it is from the peak wavelength.

As the blackbody gets hotter, the peak wavelength decreases as there is more thermal energy to be given to the individual electrons, hence higher energy level transitions can be undergone.

 

[hayabusaboston]

And how does this lead to Einstein? Is it that he described the quanta of energy being "photons" and that they emit after given enough energy? ok thanks guys for the help, trials tomorrow so gotta get some sleep thanks thanks thanks.

Max planck was the original dude who discovered quantum physics, although einstein discovered the photoelectric effect

 

[o_0]

i spoke with an ex hsc marker and she said hsc students don't need to know the details, because thats really advanced quantum mechanics. The main thing you have to understand is that the curve predicted by classical theory didn't agree with the experimentally derived curve! Try have a look online if you're interested though haha

 

[DNETTZ]

And for those who do care and cant be bother to look it up, I will explain it briefly, simply and in an analogous yet erroneous fashion:

According to the second law of thermodynamics, entropy of a closed system will not decrease. Given the scale of the universe, it would then seek to equally spread energy across the entire of space, such that entropy is maximised. When a body is heated, it has thermal energy, if you like, the vibrations of the individual particle. Based on what i just said, it tries to pass this to lose energy. Thus, the black body engages in a spontaneous conversion of thermal to electromagnetic energy, which is emitted across the spectrum, including light.

The graph you describe plots intensity of emitted light against the wavelength of light emitted. As the gradient approaches infinity, therefore there is a infinite amount of small wavelength radiation emitted by the body. Bearing in mind that it is a conversion of thermal energy, and infinite amounts (intensity being the amount of it) are indicative of the energy used to create it, the classical model suggested that black body radiators effectively had unlimited energy in them they were emitting electromagnetically.

Having violated the law of conservation of energy and the 2nd law of thermodynamics, hell, even the third law, as infinity/(any energy level) is still equal to infinity [conceptually at least], they termed it the ultraviolet catastrophe.

Now, why does that graph bend down at the end by quantum mechanics? Because EMR is emitted by converting firstly thermal energy into electron energy, statistically, one will observe more occurances of the middle range, as a certain quanta of energy converted is needed to make the EMR go in the first place! Also, it tapers off to the right hand side as we dont have infinite energy!

Hope that clears things up.

 

[Alkenes]

Are you srs???!!!!

i spoke with an ex hsc marker and she said hsc students don't need to know the details, because thats really advanced quantum mechanics. The main thing you have to understand is that the curve predicted by classical theory didn't agree with the experimentally derived curve! Try have a look online if you're interested though haha