21st April 2009 - 08:08 AM
For my yr 11 physics class, i need to research and write one page of notes on 4 or different topics (including equations).
The topics i am having issues with are:
Electron Energy Shells in Hydrogen
The Basic Concepts of Quantum Physics (too much on the net!!!)
and Fluorescence and Phosphorescence
If someone could explain them to me, it would be greatly appreciated!!
21st April 2009 - 10:06 AM
Atomic hydrogen is a very simple physical system.
Both the absorption and emission spectrums of atomic hydrogen are characterized by a very simple arrangement of lines.
Every line in the spectrum is associated with a specific frequency and wavelength.
But according to pre-quantum physics there is no reason why hydrogen should have special lines in its spectrum.
Quantum physics assumes we can never know the position and momentum of any object both to unlimited precision. The more we know the position, the less we know the momentum and vice-versa.
Electrons and protons are very-very tiny. But if the electron and proton were at rest with respect to each other and the electron was just stuck on the proton, then we would know the position and momentum of the electron both. So the quantum ground state cannot be this "bottom of the potential well" as pre-quantum physics suggests. Indeed, every time we have a bound system in a potential well, the quantum minimum energy for the system is above the pre-quantum minimum energy.
Quantum physics is more just an uncertainty of position versus momentum. It also says everything is a probability which is the square of the magnitude of a function called an amplitude. The amplitude function sometimes acts like a wave moving from place to place, but in a bound system, like hydrogen, it is a trapped wave, like a rope or chain held at both ends. Just like a chain, certain modes are allowed. This means that not only is there a quantum ground state, but the other bound states have discrete energies.
The absorption and emission spectrums of atomic hydrogen can then be interpreted as reflecting the energy differences between the allowed discrete energy levels of atomic hydrogen. This leads to a new difference of quantum physics: light comes in chunks. These chunks, photons, carry a certain amount of energy corresponding to the difference of hydrogen energy levels and have a specific frequency which is proportional to the energy.
Some easy predictions: Since not-very-hot atoms are usually in the ground state, the absorption spectrum is expected to be simpler than the emission spectrum, because we don't have a rule that on emission the excited atom must immediately return to the ground state. In atoms or molecules more complicated than atomic hydrogen, the levels will be more complicated.
Fluorescence is when an atom or molecule absorbs light of one energy and emits light of a lower energy. This what the coating of fluorescent bulbs does to the UV light of mercury vapor.
Phosphorescence is like fluoresce, but takes much more than 0.01 second. Something makes it hard for the atom or molecule to return to a lower energy state.
25th April 2009 - 11:58 PM
thanks for that.
it helped me understand some of the stuff.
Alot better than what i have been finding on the web.