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HSC Physics Marathon 2013-2015 Archive (6 Viewers)

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InteGrand

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re: HSC Physics Marathon Archive

Except that we don't have anywhere near enough energy to reach anything close to relativistic speeds, so the effects are very very small. lol

(But somehow the HSC wants us to overlook this I believe.)
 

mrpotatoed

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re: HSC Physics Marathon Archive

Over time, scientists have used two theories to explain the heating of a blackbody – wave theory and quantum theory. Explain which theory best explains the heating of a blackbody today by considering the differences between them. [6 marks]
The classical theory of physics predicts that the shorter than wavelength of EMR absorbed, the more intense the radiation released. However this meant that it would violate the conservation of energy as the area under a black body curve would be infinite. The black body that was produced with experimental data showed that the curve peaked at UV instead of going off to infinity at short wavelengths, as classical physics predicted. The experimental black body curve could not be produced with classical physics mathematics.

Planck proposed that black body radiation was quantised to solve this problem. Although this assumption produced a mathematical formula that could perfectly explain experimental data, he was sceptical of it being true. Whilst classical theory states that EMR can have any range of frequencies or energies, Planck's new quantum theory stated that black body EMR has energy that is an integral multiple of its frequency. His proposal, whilst controversial, was successful in explaining the nature of the black body curve and solved the UV catastrophe that classical physics could not, and is therefore the theory that is used today.

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Outline the method used by the Braggs to determine crystal structure 3 MARKS

p.s. can someone tell me if my answers are ok
 

leehuan

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re: HSC Physics Marathon Archive

The classical theory of physics predicts that the shorter than wavelength of EMR absorbed, the more intense the radiation released. However this meant that it would violate the conservation of energy as the area under a black body curve would be infinite. The black body that was produced with experimental data showed that the curve peaked at UV instead of going off to infinity at short wavelengths, as classical physics predicted. The experimental black body curve could not be produced with classical physics mathematics.

Planck proposed that black body radiation was quantised to solve this problem. Although this assumption produced a mathematical formula that could perfectly explain experimental data, he was sceptical of it being true. Whilst classical theory states that EMR can have any range of frequencies or energies, Planck's new quantum theory stated that black body EMR has energy that is an integral multiple of its frequency. His proposal, whilst controversial, was successful in explaining the nature of the black body curve and solved the UV catastrophe that classical physics could not, and is therefore the theory that is used today.

-----

Outline the method used by the Braggs to determine crystal structure 3 MARKS

p.s. can someone tell me if my answers are ok
Wasn't my question so I can't decide as to if it's a 6/6 but it seems 5 marks are definitely there.

But instead of saying a simple formula you could just say E=hf, or put it in brackets.
 

mrpotatoed

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My understanding is E=hf actually has nothing to do with solving the UV catastrophe, or at least not that formula directly. The actual formula he used to explain it isn't in the course but with a quick google search I'm guessing its the first one on here https://en.wikipedia.org/wiki/Planck%27s_law. That formula relied on the assumption the black body EMR was quantised. Correct me if im wrong.
 

porcupinetree

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Outline the method used by the Braggs to determine crystal structure 3 MARKS
The Braggs shone a beam of X-rays at a crystal surface, which produced a diffraction pattern on a detector. When the angle of incidence was altered, the changes in the diffraction pattern allowed the Braggs to mathematically determine the spacing between successive planes of ions in the crystal structure, which in turn allowed them to determine the overall crystal structure of the substance.

Here's a new Q, can y'all tell me what else I could have added? I feel like I've included everything but at the same time I feel like it's too short.

2009 HSC 17b - "Explain how inertial and non-inertial frames of reference relate to the principle of relativity" - 3 marks
My answer:
An inertial frame of reference is one in which acceleration = 0 and Newton's first law holds true (this is not the case in a non-inertial frame of reference). The principle of relativity states that 'no experiment fully within an inertial frame of reference allows you to determine your relative velocity'. i.e., if you are in a non-accelerating frame of reference, no mechanical experiment (e.g. hanging a pendulum) will allow you to determine whether you are stationary, or moving at a constant velocity.
 

iforgotmyname

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re: HSC Physics Marathon Archive

The classical theory of physics predicts that the shorter than wavelength of EMR absorbed, the more intense the radiation released. However this meant that it would violate the conservation of energy as the area under a black body curve would be infinite. The black body that was produced with experimental data showed that the curve peaked at UV instead of going off to infinity at short wavelengths, as classical physics predicted. The experimental black body curve could not be produced with classical physics mathematics.

Planck proposed that black body radiation was quantised to solve this problem. Although this assumption produced a mathematical formula that could perfectly explain experimental data, he was sceptical of it being true. Whilst classical theory states that EMR can have any range of frequencies or energies, Planck's new quantum theory stated that black body EMR has energy that is an integral multiple of its frequency. His proposal, whilst controversial, was successful in explaining the nature of the black body curve and solved the UV catastrophe that classical physics could not, and is therefore the theory that is used today.

-----

Outline the method used by the Braggs to determine crystal structure 3 MARKS

p.s. can someone tell me if my answers are ok
I think you forgot the fact that he said EMR exsists in packets where the energy of each packet is defined by e=hf, he also hypothesised that there is more low energy (low frequency) packets than High energy/frequency packets. Moverover, high frequency packets need more energy to activate, low need less energy to activate. So thats how he explained the experimental reults
 

Drsoccerball

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re: HSC Physics Marathon Archive

The Braggs shone a beam of X-rays at a crystal surface, which produced a diffraction pattern on a detector. When the angle of incidence was altered, the changes in the diffraction pattern allowed the Braggs to mathematically determine the spacing between successive planes of ions in the crystal structure, which in turn allowed them to determine the overall crystal structure of the substance.

Here's a new Q, can y'all tell me what else I could have added? I feel like I've included everything but at the same time I feel like it's too short.

2009 HSC 17b - "Explain how inertial and non-inertial frames of reference relate to the principle of relativity" - 3 marks
My answer:
An inertial frame of reference is one in which acceleration = 0 and Newton's first law holds true (this is not the case in a non-inertial frame of reference). The principle of relativity states that 'no experiment fully within an inertial frame of reference allows you to determine your relative velocity'. i.e., if you are in a non-accelerating frame of reference, no mechanical experiment (e.g. hanging a pendulum) will allow you to determine whether you are stationary, or moving at a constant velocity.
I think you should mention where a non-inertial frame of reference applies in this.
 

mrpotatoed

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re: HSC Physics Marathon Archive

How would E=nHF explain the UV catastrophe?
 

iforgotmyname

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The Braggs shone a beam of X-rays at a crystal surface, which produced a diffraction pattern on a detector. When the angle of incidence was altered, the changes in the diffraction pattern allowed the Braggs to mathematically determine the spacing between successive planes of ions in the crystal structure, which in turn allowed them to determine the overall crystal structure of the substance.

Here's a new Q, can y'all tell me what else I could have added? I feel like I've included everything but at the same time I feel like it's too short.

2009 HSC 17b - "Explain how inertial and non-inertial frames of reference relate to the principle of relativity" - 3 marks
My answer:
An inertial frame of reference is one in which acceleration = 0 and Newton's first law holds true (this is not the case in a non-inertial frame of reference). The principle of relativity states that 'no experiment fully within an inertial frame of reference allows you to determine your relative velocity'. i.e., if you are in a non-accelerating frame of reference, no mechanical experiment (e.g. hanging a pendulum) will allow you to determine whether you are stationary, or moving at a constant velocity.
you forgot the formula they deduced: 2dsin(theta)= n(wavelength lima) where if n=1,2,3 it underwent constructive inter and if n=1/2, 3/2... then it underwent destructive interference.

They also saw interference patterns from diffraction using photographic film/cloud chamber. If constructive= very bright, destructive= dark af. by looking at the interference patterns they are able to work out structure of lattice
 

mrpotatoed

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The Braggs shone a beam of X-rays at a crystal surface, which produced a diffraction pattern on a detector. When the angle of incidence was altered, the changes in the diffraction pattern allowed the Braggs to mathematically determine the spacing between successive planes of ions in the crystal structure, which in turn allowed them to determine the overall crystal structure of the substance.

Here's a new Q, can y'all tell me what else I could have added? I feel like I've included everything but at the same time I feel like it's too short.
You should mention that the beams fired at the nickel crystal were monochromatic (in faze), and the x-rays were used as they were similar to the spacing between the nickel atoms which is deal for diffraction. I guess you could also draw a diagram the fully shows how he worked out the spacing's between atoms, if this was in an exam situation

nvm I got beaten
 

Mathsisfun15

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How would E=nHF explain the UV catastrophe?
E=hf is more just showing how all energy emitted and absorbed by the black body is quantised which is the explanation to why it doesn't follow classical theory i.e. its saying that intensity is not proportional to frequency
 

mrpotatoed

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But how do you show e=hf is the reason the graph drops off after UV, instead of going up to infinity like a y=1/x graph? When I saw a question like this in success one, they just said Planck devised a 'mathematical formula' to explain the UV catastrophe, and the answer wasnt very detailed which suggests to me that the 'mathematical formula' isn't part of the course.
 

PhysicsMaths

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But how do you show e=hf is the reason the graph drops off after UV, instead of going up to infinity like a y=1/x graph? When I saw a question like this in success one, they just said Planck devised a 'mathematical formula' to explain the UV catastrophe, and the answer wasnt very detailed which suggests to me that the 'mathematical formula' isn't part of the course.
Explaining the shape itself is far beyond the requirements of the syllabus - the dot point asks you to identify planck's quantisation
 

Drsoccerball

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But how do you show e=hf is the reason the graph drops off after UV, instead of going up to infinity like a y=1/x graph? When I saw a question like this in success one, they just said Planck devised a 'mathematical formula' to explain the UV catastrophe, and the answer wasnt very detailed which suggests to me that the 'mathematical formula' isn't part of the course.
I think he suggested that the energy was found by integrating with boxes or someshit like that and he was able to calculate this becaused he assumed that light was quantised..
 

iforgotmyname

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Explaining the shape itself is far beyond the requirements of the syllabus - the dot point asks you to identify planck's quantisation
U can with Uni Maths... But MAths in physics is like year 7 maths... There is quite a difference there
 

porcupinetree

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you forgot the formula they deduced: 2dsin(theta)= n(wavelength lima) where if n=1,2,3 it underwent constructive inter and if n=1/2, 3/2... then it underwent destructive interference.
I talked about this in an exam once for Physics and my teacher said that it was mainly unnecessary, especially when the question is only worth 3 marks. However, you do raise a good point, and personally I reckon it'd be useful to mention the 2dsintheta stuff in an exam, especially if it's worth more than 3 marks
 

InteGrand

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But how do you show e=hf is the reason the graph drops off after UV, instead of going up to infinity like a y=1/x graph? When I saw a question like this in success one, they just said Planck devised a 'mathematical formula' to explain the UV catastrophe, and the answer wasnt very detailed which suggests to me that the 'mathematical formula' isn't part of the course.
The answer to your question is here: http://disciplinas.stoa.usp.br/pluginfile.php/48089/course/section/16461/qsp_chapter10-plank.pdf

Warning: requires university maths and physics (but that makes it more fun).

You can see this thread for some understanding: http://community.boredofstudies.org/265/ideas-implementation/336155/uv-catastrophe.html#post6937528
 

mrpotatoed

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Cheers guys.

Since theres no question:

Explain how cathode ray tubes allow the manipulations of a stream of charged particles 2 marks
 

leehuan

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That question seems rather dodgy...

Cathode rays are essentially beams of electrons (negatively charged particles with q=-1.602*10^-19C, m=9.109*10^-31kg) that are directed from an unjoined cathode and anode in a very low pressure tube. Normally, cathode rays seek to travel in a straight line, and with the use of a fluorescent display screen this pathway can be clearly observed. We can manipulate charged particles through observing the fluorescent display screen when we include an electric field or magnetic field which deflects it, or by inserting a paddle wheel to observe how they carry momentum.

When are they going to change momentum to thermionic effect...
_______________________________________________
NEXT QUESTION:
a) Explain the forces involved when a spacecraft is being launched into orbit. (3)
b) Explain the forces involved when a spacecraft is in orbit AND during reentry. (5)
c) Discuss the necessity of having a spacecraft reenter at a specific range of angles. (4)
 
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