Syllabus Help (1 Viewer)

[allGenreGamer]

Ok, I'm nearly ready to take on the HSC Physics exam. However, I still need help with some of the syllabus dot-points:

1) Discuss advantages/disadvantages of AC and DC generators and relate these to their use.
2) Discuss Einstein and Planck's diffring views about whether science research is removed from social and political forces.
3) Analyse the significance of the hydrogen spectrum in the development of Bohr's model of the atom.
4) Describe how Bohr's postulates led to the development of a mathematical model to account for the existence of the hydrogen spectrum.
5) Describe Fermi's initial experimental observation of nuclear fission.
6) Describe Fermi's demostration of a controlled nuclear chain reaction in 1942.

Thanks heaps!

 

[Xayma]

1) AC:
Advantages:
Voltage easily changed
Slip rings do not wear out quickly

Disadvantages:
Often must spin at a determined speed (most appliances running on 50Hz)

DC:
Advantages:
Can spin at any desired speed

Disadvantages:
Split ring commutator wears out quickly and needs to be maintained.
Voltage produced is not easily changed.

2)Einstein: Pacifist, condemed the German war effort, believed scientifc research should be conducted with how it will be used in mind.

Planck: Nationalist, supported the German war effort, believed that scientific research should take place purely for science's without worrying about how it may be used.

3) The hydrogen spectrum giving discrete finite number of lines, suggested that electrons moved between set energy lines, with quantisied energy given off/absorbed when a movement between these lines occured.

4) The idea that spectral lines were caused by quantisied packets of energy produced from a change in a stationary state of an electron allowed an empirical formula to be produced by Balmer and later adapted by Rydberg.

5) Fermi bombarded U-235 with neutrons after splitting Fermi recorded β decary. Fermi incorrectly made the assumption that an element higher than 92 was created. The β decay was a result of the nuclear decay of the daughter elements created due to the splitting of the U-235 nucleus.

6) Enrico Fermin on December 2,1942 demonstrated at a disused squash court under the University of Chicago a controlled nuclear chain reaction at "Chicago Pile No. 1"

The moderator used to slow the neutrons consisted of of bricks of graphite.

The reactant was 850 tonnes of natural uranium in 22000 slugs.

A few minutes after 3:25pm the reaction became self-sustaining and was left for 28 minutes before the reaction was stopped.

 

[Tommy_Lamp]

2) Although there was no direct debate between Einstein and Planck on this issue, it seems that Einstein and Planck took different views about scientists remaining in Germany during the Nazi era and continuing to do scientific research.

Planck stayed on and directed the Kaiser Wilhelm Institute. Einstein and others left Germany. Although there was no direct correspondence between Einstein and Planck, consideration of the actions of each provides a case study of the complexity of evaluating the moral responsibility of science to social orders.

3) This is significant in Bohr's second postulate, i.e. When an electron falls from a higher energy level to a lower energy level, it emits energy that is quantised (E=hf). The emission (or absorption) of energy is discontinuous and corresponds to a transition between two stationary states.

4) The Bohr model supplied an experimental basis for the Balmer series formula (Rydberg's equation).

5) Fermi bombarded many of the known elements with neutrons. In the majority of cases new isotopes were formed. Of particular importance was the bombardment of Uranium-238, which produced U-239, which Fermi thought would undergo beta decay to form the first transuranic element:

6) This might be wrong: He had massive piles of graphite blocks, which absorbed 2 of the 3 neutrons released by the uranium. The one that didnt get absorbed hit another uranium atom etc. etc.


EDIT: Xayma posted while i was typing up my response

 

[mojako]

To Xayma:
In (5), did they also produce a small amount of transuranic elements?
In (6), Jacaranda has it as 50 tonnes not 850 tonnes... isn't 850 tonnes too massive though? The 50 tonnes uranium were dispersed throughout 400 tonnes of graphite.
http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/First-Atomic-Pile.html btw

To Tommy_Lamp:
In (4), isn't it a theoretical basis?

 

[Xayma]

5) It is irrelevant, but yes it probably did contain some as well but not enough for the results.

6) Probably, I probably copied it down wrong Ill check it later.

 

[sHin]

4) The idea that spectral lines were caused by quantisied packets of energy produced from a change in a stationary state of an electron allowed an empirical formula to be produced by Balmer and later adapted by Rydberg.

My understanding is that Balmer/Rydberg derived the empirical formula for hydrogen spectrum lines without using quantum theories. Bohr then came along and realised, after viewing the hydrogen spectrum, that the spectrum lines were a result of quantised energy.

Bohr then came up with his three postulates. Using these postulates, he came up with an equation that resembled the Balmer/Rydberg equation, hence, supporting his model of the atom.

 

[Jase]

yes.. the balmer eqaution came first through experiment empirical derivation. (n^2 / n^2 -2)
Bohr found theoretical evidence supporting it and *RE*derived it.

With syllabus points like that in a test, you highlight the key words and just write as much as you know about it. It works.
'Bohrs postulates'- state them all and link them to Rydbergs equation which is the 'mathematical model'. Then fart on about the 'hydrogen spectrum' and how this model explains it. So.. some postulates -> energy levels + absorption. *blahblah* This gave theoritical evidence for balmers and rdybergs equation. The spectra are a result of the absorption and emission and can be calculated by rydbergs eq. *crap on about spectra a bit more* . Thats for a 3-5 mark question.

 

[Xayma]

My understanding is that Balmer/Rydberg derived the empirical formula for hydrogen spectrum lines without using quantum theories. Bohr then came along and realised, after viewing the hydrogen spectrum, that the spectrum lines were a result of quantised energy.

Bohr then came up with his three postulates. Using these postulates, he came up with an equation that resembled the Balmer/Rydberg equation, hence, supporting his model of the atom.

But saying led to implies that the postulates were the reasoning behind the mathematical model. Balmer's original equation may just have been manipulated to include the quantum numbers after Bohr published his postulates.

 

[Jase]

Oh and pay attention to the keywords. especially on number 3.
Analyse the significance - it may not be enough to just state what the hydrogen spectra had to do with Bohr.
You could say, the hydrogen spectrum was extremely significant in the development of Bohr's model, since it provided both theoretical and experimental evidence.
The spectra first led to the deriving of Balmer's eqaution, which was important in supporting Bohr's work on the hydrogen spectra. and then mabye go on about the specifics of his postulates and the spectra.

 

[Jase]

But saying led to implies that the postulates were the reasoning behind the mathematical model. Balmer's original equation may just have been manipulated to include the quantum numbers after Bohr published his postulates.

hmm. im pretty sure Balmer's and Rydberg's orginal eqautions always existed in their respective forms. They were just unaware of the theory behind the principal quantum number, but their experiments obviously showed the theory. Bohr then derived it using the his hypothesis, and that gave evidence for his postulates.

 

[Xayma]

So you would talk more about the mathematical model of the energy levels of the electron orbits? Such as -13.9eV?

 

[Jase]

Well.. not exactly about the specific energy levels.
I'd just touch on Rydberg's eqaution and the way that it clearly shows excited atoms release these specific energies. Once bohr verified this with theory, then it was safe to go on and account for the spectra.

(im assuming that by' mathematical model', it means an eqaution i.e. Balmers and Rydbergs, that can predict the spectral lines, right?)

 

[sHin]

2004 Jackaranda Physics: pg. 430
Balmer's equation is an empirical equation. A theoretical equation derived from Bohr's model of the atom now agrees with the empirical equation. This is a major achievement and offers strong support for the Bohr model.

When mathematical model is mentioned, I think it is referring to what Bohr derived using his postulates. As the above states, Balmer's equation was an empirical equation. A formula that simply "worked" without any theoretical basis behind it.

What Bohr derived was a true mathematical model based on theory.

Anyone agree?

 

[Constip8edSkunk]

for pt 4, balmer simply plugged in numbers to get his equation, but the dot pt is prolly after how bohr explained, using his postulates, the spectra lines, and his derication/confirmation of the empirical eq. balmer got (theres a description of this in macmillan if i remember correctly)