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# phy4 help, stationary waves with electrons watch

1. Q) Descrive fully about stationary waves existing in an atom in terms of the electrons. [4 marks, excluding clarity]
2. If the electron wasnt in a stationary wave it would gradually loose energy and spiral towards the positive nucleus. In a standing wave there is no net flow of energy and so the electron can maintain an orbit. The wave has a wavelength the same as the diameter of an atom, 1*10-10m.
I DNT KNW WAT ELSE TO SAY...4 Marks... i think i wud get 2/4
3. i would say this:
1) electrons act as standing waves
2) more waves found in higher orbits

That's all i know for 2 marks
4. The most important thing is:

The (discreet) energy levels of electrons correnspond to the number more stationery waves created.
5. (Original post by nas7232)
Q) Descrive fully about stationary waves existing in an atom in terms of the electrons. [4 marks, excluding clarity]
> the electron can be modelled as a looped stationary wave (ie. with the end antinodes being joined to form a circle)
> the energy of the electron corresponds to the energy of the stationary wave
> harmonics of the fundemental frequency of this stationary wave represents higher energy levels
> harmonics are discrete and therefore so are energy levels

I'd put those four, of course not in bullet form cos I would want the clarity mark.
6. (Original post by nas7232)
Q) Descrive fully about stationary waves existing in an atom in terms of the electrons. [4 marks, excluding clarity]
I would say something along the lines of:

-The electrons act as stationary waves (De Broglie wavelength and all that)
-The electrons' orbit's have to be equal to a whole number of wavelengths
-If this was not the case, then the electron going round in it's orbit would interfere with itself and cancel out (superposition)
-This is why electrons can only exist in specific discreet energy levels
-Each energy level corresponds to a multiple of the electron's wavelength (ie λ, 2λ, 3λ... etc)

Hope that helps!
7. "If this was not the case, then the electron going round in it's orbit would interfere with itself and cancel out (superposition)"

I haven't heard of that explanation before... I just thought there had to be a whole number otherwise there would be no wave, and very small amplitude. Is that the same thing as the superposition you mean?
8. can anyone tell me what the name of this topic is, any names for this or is it just under de broglie cos i need to do some research bout this on the net b4 thursday my revision book has a minor few sentances about it, very basic explanation !
9. (Original post by mik1w)
"If this was not the case, then the electron going round in it's orbit would interfere with itself and cancel out (superposition)"

I haven't heard of that explanation before... I just thought there had to be a whole number otherwise there would be no wave, and very small amplitude. Is that the same thing as the superposition you mean?
yeh i spose - if it wenr't same no of wavelengths, wouldn't you agree that interference would occur when the waves made their way around?
10. no, it is only one wave, I only know of interference between two waves... how can a wave interfere with itself?
11. only way you can do that if you have the wave reflected from an object in the opposite direction of the wave in order to cause constructive superposition.
12. (Original post by nas7232)
only way you can do that if you have the wave reflected from an object in the opposite direction of the wave in order to cause constructive superposition.

Not always constructive. Could also be destructive. All depends on the level of intensity of the incident and reflected waves. If the distance between the source and reflecting surface is small, the lesser is the interference. Thusforth, distance between the two plays a vital role for the interference of one way with it's reflected self.

I think the electron question is quite a toughy. Sonja has answered it well. You guys are incredibly sick at this subject. Never ever do Economics AND Physics at AS/A2. Too late now I suppose. Darn darn darn darn.
13. oh, i was on about creating a stationary wave. Maths and physics all in 1 year is tough too
14. ok here is what I would answer first of all
- the wavelength of an electron or debroglie-wavelength is equal to diameter of atom
-you cant find an electron in the neuclues or out side the energy level
-the electrons move between the energy level and the nuclues forming a stationary wave as they exist in premitted/discreated energy levels,apremitted
-maximum electrons can be found in the position midway between the neuclus and the energy level thus the edge of the neuclus and energy level are the nodes
15. (Original post by mik1w)
> the electron can be modelled as a looped stationary wave (ie. with the end antinodes being joined to form a circle)
> the energy of the electron corresponds to the energy of the stationary wave
> harmonics of the fundemental frequency of this stationary wave represents higher energy levels
> harmonics are discrete and therefore so are energy levels

I'd put those four, of course not in bullet form cos I would want the clarity mark.
i totally agree to that answer
16. Is this a synoptic question?
17. phy4 question:

mik1w answer is as good as you can get it. "If the electron wasnt in a stationary wave it would gradually loose energy and spiral towards the positive nucleus" this is true also, but i'm not sure if it will get the marks from looking at markschemes [probably more relevant to phy6 type question].
18. (Original post by mik1w)
"If this was not the case, then the electron going round in it's orbit would interfere with itself and cancel out (superposition)"

I haven't heard of that explanation before... I just thought there had to be a whole number otherwise there would be no wave, and very small amplitude. Is that the same thing as the superposition you mean?
Yes you're right, there has to be a whole number of wavelengths otherwise you don't get a wave. I was just saying that if there wasn't a whole number then the wave would interfere with itself and cancel out, so it just can't be like that. I think of it as the wave going round in a circle: if the orbit wasn't a whole number of wavelengths, then where the wave completes once full circle, it doesn't join up exactly to where it began... so it kind of crosses over itself and you get destructive interference.
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