Planck and Black Body Radiation (1 Viewer)

[Dash]

I know this is probably simple to some people,
but I'm full struggling to undertand wtf it is all about...

My question is...

How does Planck's quantum theory account for the
relationship between the dominant wavenlength
of EMR emitted by a black body and its temperature???

An answer plz!!!

ThAnX

 

[Rahul]

this is an attempted sabotage, u'll not beat me biatch,

it didnt.

lol, i'll post my explanation. it confusing and fuxed. we need help.

that bell-graph shows how the energy that is radiated reaches a maximum, which is related to the temp of the blackbody. now the classical theory was that the radiation of energy would infintely increase right, so that didnt fit the graph. in the case of classical physics, the radiation should have kept on increasing. the 'quantum' of energy would show the peak in the amount that can be radiated.

how would the dominant wavelength come into it? jus the radiation emitted. doesnt the blackbody emit radiation of all EMR?

 

[Ragerunner]

to make it sound easier the first part you said Rahul,

have an example in a solar cell

Classical theory though that if you left light shining there for a long time the thingy will increase ( i can't find the word for it )

How ever its not true such that if you leave light there nothing will increase, explaining light is quantised

you have to look at that graph and compare it to classical physics and modern.

Increase intensity of light = more current flow
Increase Frequency = higher stopping voltage and more kineteic energy

 

[Dash]

Errr... what?

Sorry, I think that I wasn't specific enough, cos what your saying is making no sense to me at all

The amount of energy radiated reaches a maximum at a particular wavelength of around 200-400nm depending on the temperature of the BB. Now, how did the quantum theory explain this?

How is it that the idea that radiation is emitted in discrete packets of energy account for this irregular pattern?

Has it got something to do with photon energy levels???
I dunno! Explain plzz! Exams soon

ThAnX

 

[Constip8edSkunk]

in short, quantum theory states that energy is emitted in discrete packets, each with energy proportional to frequency. as the frquency of the EMR increases, each quantum/photon would contain greater energy, and hence less number of photons r emitted. the intensity/radiance is dependant on the number of photons, therefor less photons of higher energy=less intensity of the corresponding radiation. search this forum 4 more detailed stuff...

 

[+:: $i[Q]u3 ::+]

the bos leaves a bit of a gap.

1. the experiments show a bell graph.
2. classical physics can't explain it.
3. planck thinks up a groovy new hypothesis about the quantisation of radiation.
4. his hypothesis can explain results~

dash, are u asking about the bit between 3 and 4, as in, how did this hypothesis actually explain the radiation?
no textbook will go out of its way to explain it - and hsc won't ask it. it's a bit advanced for this course, methinks... at least, that's what i've been told... (does anyone really know?)

 

[Dash]

argh!

Omg all that stressing for nothing!

Thanx for clearing that up +:: $i[Q]u3 ::+

I was kinda worried there... But from what i've read so far
I think that it has to do with photon energy levels and the
properties of black bodies...

O well, on to bigger things!

 

[deyveed]

Hey I'm not done yet!

What does that bell curve graph suggest?
How do you read it?
What is being experimented and how?
Can somebody give me an analogy to help clear it up?

Sorry if i sound pesky

 

[Huy]

Planck and Black Body Radiation (BBR) - The Quantum Theory

A black body is a perfect emitter or absorber of energy. It had been long known that there was a relationship between the dominant wavelength of electromagnetic radiation emitted by a hot object and its temperature.

Physicists, using classical physics could not get an agreement between theory and experiment to explain the black body radiation curve. A radical change in approach was needed. This was the quantum theory of physics.

Planck found that he could only get the necessary agreement between theory and experiment for black body radiation by making a fundamental change to the laws of physics.

He proposed that: Radiation (energy) is not emitted or absorbed by a black body continuously as classical physics said it should, but rather it is emitted or absorbed in little bursts or packets of energy quanta or photons of energy.

Mathematically, E = hf
Where E is the energy of the photon,
h is a constant called Plancks constant (6.6 x 10^-34 J.s), and
f is the frequency.

The concept that energy is quantised, lies at the heart of physical theories.

 

[deyveed]

Dominant wavelength? whats that? Is that the peak of the graph?

My friend told me to imagine this:

I get a hot object (2500K) and a machine that makes EMR with a knob that can change the frequency/wavelength. When i point that machine to the hot object with a high wavelength, it does not glow very brightly. But when i tune the machine to a specific wavelength (the wavelength of the peak), the object glows very brightly.

Is that correct??

 

[Huy]

Originally posted by deyveed
Dominant wavelength? whats that? Is that the peak of the graph?

Yes.

I don't know about your friend's explanation though, sorry