HSC Physics Marathon 2013-2015 Archive (7 Viewers)

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Drsoccerball

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re: HSC Physics Marathon Archive

someth1ng said:
lol, no - you don't have apparent weight in space.

The question is worded really badly thought - it could mean "which one is the best description for weightlessness" in which A and D both qualify as weightlessness. If you are accelerating at the rate of all acceleration of all weight forces combined, you get weightlessness.

If the question wants to ask for the "best description of the least weight force", D is the better answer.

The thing is, weightlessness is NOT the absence of a weight force - it's the absence of something that opposes gravity (ie usually a normal force).
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weight = mass x gravity therefore if theres gravity acting upon it, it has weight
 
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With option D, it depends what they mean by halfway. Usually with halfway, it means right in the middle. But Earth's gravity is stronger than the Moon, isn't it? So if you were halfway between, you'd be more attracted to the Earth than Moon, and not have a net force of 0 acting on you.

The other possibility is that by 'halfway', they meant the distance such that you had equal gravitational attraction to the Earth and Moon. But saying 'halfway' in that case is misleading.
 
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re: HSC Physics Marathon Archive

InteGrand said:
With option D, it depends what they mean by halfway. Usually with halfway, it means right in the middle. But Earth's gravity is stronger than the Moon, isn't it? So if you were halfway between, you'd be more attracted to the Earth than Moon, and not have a net force of 0 acting on you.

The other possibility is that by 'halfway', they meant the distance such that you had equal gravitational attraction to the Earth and Moon. But saying 'halfway' in that case is misleading.
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This is true, however, halfway between the moon and Earth has less of a gravitational force than any other option.
 
Librah

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re: HSC Physics Marathon Archive

InteGrand said:
With option D, it depends what they mean by halfway. Usually with halfway, it means right in the middle. But Earth's gravity is stronger than the Moon, isn't it? So if you were halfway between, you'd be more attracted to the Earth than Moon, and not have a net force of 0 acting on you.

The other possibility is that by 'halfway', they meant the distance such that you had equal gravitational attraction to the Earth and Moon. But saying 'halfway' in that case is misleading.
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Still falling towards Earth, so either way it doesn't matter to the question asked, person will still experience "apparent weightlessness".

Drsoccerball said:
But you still have apparent weight in space
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What's "apparent weight?" Do you mean just weight?
 
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Drsoccerball

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re: HSC Physics Marathon Archive

Librah said:
Still falling towards Earth, so either way it doesn't matter to the question asked, person will still experience "apparent weightlessness".



What's "apparent weight?" Do you mean just weight?
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yeah arn't they the same thing?
 
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John Bardeen, Leon Cooper and Robert Schrieffer gave a theoretical explanation for this phenomenon in 1957.
Discuss the BCS theory, using at least one diagram.

[5 marks]

Kaido asked this question a few pages back but no-one answered, can I ask it again?
 
Crisium

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Let's get this up and running again

Outline Thompson's experiment to measure the charge/mass ratio of an electron (2 Marks)
 
porcupinetree

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Crisium said:
Let's get this up and running again

Outline Thompson's experiment to measure the charge/mass ratio of an electron (2 Marks)
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Thomson set up a cathode ray tube featuring both a magnetic and electric fields which deflected the cathode rays in opposite directions; by adjusting the strengths of these fields so that they cancelled each other out, he could determine the velocity of the electrons in the beam by equating the forces from each field. He then switched off the electric field, allowing the electrons to curve in an arc due to the magnetic field, and equated the centripetal force with the magnetic field force to find an expression for the charge to mass ratio of an electron in the beam.
 
porcupinetree

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Both Max Planck and Albert Einstein, in the early to mid 20th century, had strong views about the role of science in the lead-up to war. Discuss Planck's and Einstein's differing views about whether scientific research is removed from social and political forces. 5 marks
 
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keepLooking said:
John Bardeen, Leon Cooper and Robert Schrieffer gave a theoretical explanation for this phenomenon in 1957.
Discuss the BCS theory, using at least one diagram.

[5 marks]

Kaido asked this question a few pages back but no-one answered, can I ask it again?
Click to expand...
The BCS theory is used to describe the movement of electrons in a Type 1 superconductor when it's temperature is below its critical temperature.
  1. Electrons travel through the lattice of a superconductor in Cooper pairs
  2. The first electron in a Cooper pair attracts the lattice as it passes through a gap in the lattice
  3. This creates a positive region in the lattice
  4. The second electron is attracted to the positive region, and accelerates forward
  5. The lattice returns to its normal shape due to elasticity
  6. Thus, the electron pair can travel through the lattice unimpeded
As the electrons can travel through unimpeded, the superconductor has zero resistance while it is below its critical temperature.
Since I can't draw a picture here, here's one I think is suitable:


Is that enough for 5 marks? Or would you need something else?
 
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PhysicsMaths

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rand_althor said:
The BCS theory is used to describe the movement of electrons in a Type 1 superconductor when it's temperature is below its critical temperature.
  1. Electrons travel through the lattice of a superconductor in Cooper pairs
  2. The first electron in a Cooper pair attracts the lattice as it passes through a gap in the lattice
  3. This creates a positive region in the lattice
  4. The second electron is attracted to the positive region, and accelerates forward
  5. The lattice returns to its normal shape due to elasticity
  6. Thus, the electron pair can travel through the lattice unimpeded
As the electrons can travel through unimpeded, the superconductor has zero resistance while it is below its critical temperature.
Since I can't draw a picture here, here's one I think is suitable:


Is that enough for 5 marks? Or would you need something else?
Click to expand...
From what you're saying, it seems like you're implying that the there is zero electrical resistance due to the elasticity of the lattice?
But rather, what you should relate this to is the formation of cooper pairs, and it's due to the idea that each electron goes on to form cooper pairs with other electrons, forming a large network of interactions. If one pair were to collide with the lattice, the entire network will also collide, which is too energetically costly, so they must therefore move through the lattice unimpeded.
So probably move your statement about the cooper pairs down a few steps, and explain how they are formed (vibrations in the lattice and the transmission of phonons)

I also think you should start with individual electrons (instead of cooper pairs) and basically mention that the phonon transmission that occurs in the concentrated positive region of the lattice enables the electrons to overcome the electrostatic repulsion (caused by the opposing charges) and hence form cooper pairs
 
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iforgotmyname

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Kaido said:
An observer on Earth watches two spaceships. According to their measurements, spaceship A is travelling away from Earth at 0.5c, and spaceship B is approaching Earth at 0.75 c. How fast is spaceship A moving according to the crew on spaceship B?

(2015ers only, trollface.jpg)
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0.25c backwards
 
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Drsoccerball

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Theres a formula you substitute it in ive trolled my physics teacher so many times with this trying to piss him off...
 
Crisium

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Yo people I've been teaching myself From Ideas to Implementation (I am up to section 4 atm)

I just need some clarification in regards to section three and the band theory

Some textbooks say that the conduction band and valence band OVERLAP whilst others say that they are COMBINED, or say that the FORBIDDEN ENERGY GAP IS NON-EXISTENT in a conductor

(I feel as if it is the former and then I could mention it in regards to the latter - In conductors the conduction band and valence band overlap, meaning that the forbidden energy gap in non-existent, etc. The "combined" just doesn't sound right)

These seem like three completely different ways to refer to it but I was wondering if they could be used synonymously in this context?

If not, which is preferred?
 
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