Naked Science Forum
On the Lighter Side => New Theories => Topic started by: sorincosofret on 04/12/2008 04:56:01
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Franck Hertz experiment and quantum hypothesis
The Bohr conception about an atom with discrete levels of energy was verified through Franck-Hertz experiment, first performed in 1914. Franck and Hertz bombarded isolated atoms with electrons and showed that the electrons lost discrete amounts of energy, characteristic for each element. Further, they were able to show that electron bombardment at an appropriate energy led to optical emission at the known spectral frequency corresponding to that energy.
Using a device presented in fig 1 they observed maximal and minimal in the transmission of electrons through mercury vapor, with increasing potential of acceleration of these electrons.
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Figure 1 Schematic diagram of the Franck-Hertz device
Electrons are accelerated toward a grid through a sealed tube containing mercury at low pressure. When the accelerating voltage, V, is increased, a current is first observed when V exceeds 1.5 V (fig. 2).
The current intensity increases with increasing of potential up to a certain threshold voltage, at which point the current drops sharply. The reason for this is that the kinetic energy, acquired by an electron matches the energy difference between the ground state and an excited state of the mercury atom. If the energy of the electrons in the beam is less than the energy separation of the ground state from the first excited state, then no energy is transferred and the collisions are elastic. If the beam energy is equal to or greater than the separation of the lowest states, then energy is absorbed, an electron is promoted on an excited state, and the collision is inelastic. If we increase again the potential after first drop the current again starts to rise until it reaches a value when it drops sharply again. Now the electron has undergone two sequential inelastic collisions.
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Fig. 2 Dependence of current on accelerating potential
The experiment suggests that the mercury electrons cannot accept energy until it reaches the threshold for elevating them to an excited state. This 4.9 volt excited state corresponds to a strong line in the ultraviolet emission spectrum of mercury at 254 nm. Drops in the collected current occur at multiples of 4.9 volts since an accelerated electron which has 4.9 eV of energy removed in a collision can be re-accelerated to produce other such collisions at multiples of 4.9 volts. This experiment was strong confirmation of the idea of quantized atomic energy levels.
Why the actual explanation is wrong
A true theory of physics should clarify some simple facts:
• How gain an electron a kinetic energy according to quantum mechanic.
• How loose an electron an kinetic energy (totally or partially) according to quantum mechanic
• Is it possible to be formulated a gegen-experiment to actual Franck-Hertz experiment?
According to quantum mechanic, an electron, like any quantum particle, can gain or loose energy as multiple of Planck constant. Actual physics should clarify when and how an electron in an electric field receives these quanta of energy. An electron acted by a difference of potential U, receive a single quanta of energy or receive more? These quanta are increasing the energy of electron in a single step or in multiple steps? There are a lot of questions but is not the case to insist here.
For the present discussion we consider that an electron acted by a difference of potential U receive this energy as a whole.
If the incoming electron has a kinetic energy (KE) which is less than the difference ground and excited mercury energy levels (ΔE), then it simply bounces off elastically, keeping all its original kinetic energy as in fig. 3. This is the case when KE is smaller then 4,9 eV, and in this case even actual quantum mechanic admit a ,,classic” comportment of electron.
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Figure 3.
If the electron has KE equal to ΔE, the mercury atom becomes excited. An electron is raised up on an excited level and the entire energy of electron is transferred to atom as in fig. 4. Of course it is implicitly supposed that energy of electron is formed by a unique quantum of energy. The excited atom is not stable and after a smaller or longer time interval, it falls on the ground state with emission of a photon.
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Figure 4.
The absurdity of actual quantum explanation can be observed when the electron KE is greater then ΔE. If the energy of electron is formed by a single quanta it is impossible to explain how a part of kinetic energy is used for atom excitation and other part remain to electron and contribute to gas conductibility.
For example, an electron with a KE equal with 6 eV, excite an mercury atom using 4,9 eV, and the electron remain with 1,1 eV as in fig. 5. Further this electron suffers elastic collision with other mercury atoms and consequently, the conductibility of gas is increased.
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Figure 5
In case of an electron with a KE equal with 6,1 eV, after atom excitation, the electron remain with 1,2 eV. Actual quantum mechanics should explain the mechanism of this quantum split. If the energy of electron is considered quantified, and formed by a single chunk, this split works against quantum theory itself. Of course it can be admitted that energy of electron is formed by multiple quanta. But in this case how can an electron fit its sum of chunks to transfer only a certain quantity to a mercury atom. Entering more into details, the chunks which form the kinetic energy of electrons are forming a photon quantum in certain cases. In this case the actual quantum is not the smallest chunk and another theory of physics should be accepted. These are the actual orthodox prediction. The same discussion should be performed in case of photoelectric effect, with specification of role reversal.
In the proposed theory, the electron circulation, if there exists, plays a secondary importance. In the proposed theory, the variation of electric field and consequently the variation of free electrons KE are continuous. In order to become free an electron from an atomci structure, need certain energy (ionization energy) and the entire photoelectric effect or the ionization process can be explained in classical physics. In order to convince actual elites about absurdity of actual orthodox model of Frank-Hertz experiment a gegen experiment is proposed.
The idea of proposed experiment:
If the electrons are responsible for mercury atom excitation, the same phenomena should be observed using other sources of electrons, for example, a source of beta radiation.
It is known that beta radiations are electrons with high energies. This beam of energetic electrons can be slow down to electrons with energies up to 50 eV using different techniques (decelerating in electric field, bremsstahlung emission etc.). After that, these electrons with low kinetic energies are directed to a low pressure mercury gas and the excitation of mercury atoms followed by light emission of specific quanta is counted.
For the actual orthodox theory, there is no difference between an electron beam originating from a gas discharge tube and from a radioactive source; the effects should be identical.
In the new proposed theory, the results are completely different for a beam of electrons coming from a radioactive source, and a ,,beam” emitted by a cathode gas tube, even both beams has the same energies.
A beam of electrons coming from a radioactive source will never produce a specific line excitation of mercury or other atoms. At low energies, up to 50 eV, an electron beam coming from a radioactive source is scattered by atoms, without any photon emission. At higher energies a continuous spectrum of photon energies is counted (brehmstrahlung radiation).
The detailed explanation of Franck Hertz experiment and Photoelectric effect is described in Corpuscular theory of light book. In the old Atomic structure book, these explanations were formulated at concept level without a detailed discussion.
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This asertion isn't true "According to quantum mechanic, an electron, like any quantum particle, can gain or loose energy as multiple of Planck constant."
An unbound electron can have any energy it likes and it can change to any other energy.
The answers to these questions
"How gain an electron a kinetic energy according to quantum mechanic.
How loose an electron an kinetic energy (totally or partially) according to quantum mechanic "
are well understood and involve virtual photons transfering the energy.
I have no idea what "Is it possible to be formulated a gegen-experiment to actual Franck-Hertz experiment?" means.
"physics should clarify when and how an electron in an electric field receives these quanta of energy. An electron acted by a difference of potential U, receive a single quanta of energy or receive more? These quanta are increasing the energy of electron in a single step or in multiple steps? There are a lot of questions but is not the case to insist here.
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Physics does clarify this. It's called time dependent perturbation theory.
"In case of an electron with a KE equal with 6,1 eV, after atom excitation, the electron remain with 1,2 eV. Actual quantum mechanics should explain the mechanism of this quantum split. If the energy of electron is considered quantified, and formed by a single chunk, this split works against quantum theory itself. "
As I said before, an unbound electron's energy is not quantised. There isn't a problem here apart from you not understanding the physics.
Your propsed exeriment isn't practical anyway. The beta particles are emited with a huge range of energies. you could only hope to select that tiny band within about 0.1eV of eachother to do the experiment. You would need a very intense source of beta particles and then throw practically all of them away. The Xrays from the bremstrallung would ionise all the gas and you would get meaningless results.
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A real physical model should explain a simple thing: how is possible for a Franck Hertz tube to have a electric current and a gas discharge at 5V potential and for a common gas tube there are necessary hundreds of volts. The detailed explanation is in the book.
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The voltage is irrelevant. It is the voltage gradient (or field) which determines whether or not electrons will start moving away from the space charge around the cathode. Just use a short tube. Their final KE (in eV) depends upon the Potential Difference. If one happens to be interested in energy levels of a few volts, why use hundreds of volts of HT?
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You have right when the voltage is a ,,generic term" like voltage of atmosphere point. But speaking of Frank-Hertz tube, it is by default considered the cathode at 0V and the anode at increasing voltage. So the 5 V is the voltage of anode related to cathode. Your comment does not change the situation. A current of amperes size and few volts does not permit gas conduction in a gas tube (except so called tunnel effect for small distances between anode and cathode), but a microampere current and high voltage will produce a visible effect in a gas tube.
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"A real physical model should explain a simple thing: how is possible for a Franck Hertz tube to have a electric current and a gas discharge at 5V potential and for a common gas tube there are necessary hundreds of volts."
Because this tube has a heated filament to produce free electrons. Any field will then get them to move.
Ordinary gas tubes don't so they have to rely on the avalanche efect.
If you knew any physics worth speaking of you would have realised this.
Also you would know that this description "A current of amperes size and few volts does not permit gas conduction in a gas tube" is not far from the state of affairs in an acr welder.
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So?
If you have a high voltage across the tube you can expect many collisions on the journey with a correspondingly large number of photons emitted. The electrons slow down after each inelastic collision then speed up again under the influence of the field. And, as BC says, the avalanch effect produced lots more light. That's what a flourescent tube is designed to do!
If you are trying to look at what a single collision involves then you use a low voltage - to avoid confusion. (It may have confused you, tho, sorin/
I don't see what you are complaining about. Have you invented something new (yet again)?