HSC Physics Question Thread

[austv99]

Would appreciate if someone could check my response to this question. Just to make sure if what im saying is accurate and/or if im missing on some bits of info. TIA

Assess the contributions made by Heisenberg and Pauli to the development of atomic theory.

Heisenberg and Pauli both made significant contributions to the development of atomic theory.
Heisenberg’s introduction of the ‘Uncertainty Principle’, where the position and momentum of a particle cannot be simultaneously measure to exact precision contributed to addressing a fundamental property of the quantum theory. This, therefore, led to Heisenberg applying this to atomic theory where he explained that the wave nature of electrons in stable orbits proposed by de Broglie’s standing wave represented the probabilities of an electron’s position. From this, he devised matrix mechanics to explain the quantum probabilities of the electron’s position (electron clouds), leading to an atomic theory entirely based on quantum physics rather than Bohr’s combination of classical and quantum physics.
Pauli’s introduction of the ‘Exclusion Principle’ where no two electrons can exist in the same quantum state developed the understanding of energy states that electrons can take within the atomic theory. He also introduced the 4th quantum number (magnetic spin) which was useful in addressing the existence of hyperfine spectral lines in the hydrogen spectrum which proved as a limitation to Bohr’s model of the atom. Further, Pauli also suggested the existence of the neutrino to account for the distribution of energies observed in beta decay. This was later experimentally confirmed. Thus, he contributed to our understanding by suggesting the existence of another subatomic particle in atomic theory.

Judgement: Heisenberg made significant contributions as his ‘Uncertainty Principle led to him developing de Broglie’s proposal of electron waves through the introduction of quantum probabilities (electron clouds) of its position, leading to an atomic theory entirely based upon quantum physics.
Pauli made significant contributions as his ‘Exclusion Principle’ explained the quantum states of electrons. He also resolved a limitation of the Bohr model and suggested the existence of the neutrino.

[itssona]

Hey! I'll try my best with explaining this one

Ok so, yes, the thrust force remains constant (in the first stage of rocket launch anyway) and due to the law of conservation of momentum the acceleration increases as mass decreases, which is what you've said. Due to 'a' increasing however, it is G-forces that increase and not the thrust force. So for this : , they're not really. Keep in mind that G's are not determined by force but by acceleration (hence the formula G = 1 + a/9.8 ).

I'm not really sure what you mean by decreasing thrust (hopefully someone else can explain this better), but basically, when the rocket nears the end of its first stage of launch and the first rockets run out of fuel, the thrust force pretty much disappears as the rockets stop firing and detach themselves. Here, because there is a momentary absence of thrust force, the acceleration drops dramatically and astronauts thus feel a momentary lack of G-forces, or weightlessness. This is until the second set of rockets fire up.

ohh i finally get it!! oml thank you a million asdfhjkll

[pikachu975]

Would appreciate if someone could check my response to this question. Just to make sure if what im saying is accurate and/or if im missing on some bits of info. TIA

Assess the contributions made by Heisenberg and Pauli to the development of atomic theory.

Heisenberg and Pauli both made significant contributions to the development of atomic theory.
Heisenberg’s introduction of the ‘Uncertainty Principle’, where the position and momentum of a particle cannot be simultaneously measure to exact precision contributed to addressing a fundamental property of the quantum theory. This, therefore, led to Heisenberg applying this to atomic theory where he explained that the wave nature of electrons in stable orbits proposed by de Broglie’s standing wave represented the probabilities of an electron’s position. From this, he devised matrix mechanics to explain the quantum probabilities of the electron’s position (electron clouds), leading to an atomic theory entirely based on quantum physics rather than Bohr’s combination of classical and quantum physics.
Pauli’s introduction of the ‘Exclusion Principle’ where no two electrons can exist in the same quantum state developed the understanding of energy states that electrons can take within the atomic theory. He also introduced the 4th quantum number (magnetic spin) which was useful in addressing the existence of hyperfine spectral lines in the hydrogen spectrum which proved as a limitation to Bohr’s model of the atom. Further, Pauli also suggested the existence of the neutrino to account for the distribution of energies observed in beta decay. This was later experimentally confirmed. Thus, he contributed to our understanding by suggesting the existence of another subatomic particle in atomic theory.

Judgement: Heisenberg made significant contributions as his ‘Uncertainty Principle led to him developing de Broglie’s proposal of electron waves through the introduction of quantum probabilities (electron clouds) of its position, leading to an atomic theory entirely based upon quantum physics.
Pauli made significant contributions as his ‘Exclusion Principle’ explained the quantum states of electrons. He also resolved a limitation of the Bohr model and suggested the existence of the neutrino.

It's pretty good but in the judgement I'd recommend making it more explicit that BOTH Heisenberg and Pauli's work led to the develop of the CURRENTLY USED electron cloud model, hence revealing the significant impact of their work as it still resonates today.

[winstondarmawan]

Quanta to Quarks:
Would appreciate help with this question, even after reading the solutions I am confused:
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/22070347_1853706338279156_1387821905_o.jpg?oh=0c3940feff466f0fe0c62a9317c8a023&oe=59CFE3C5
Solution: https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/22095316_1853706898279100_1567201710_o.jpg?oh=55cabfc2a79f0599cc9cc6b5aa09370d&oe=59CFF432

Bump

[austv99]

Would appreciate help with part ii for both pictures- the natural radioactivity one and the nuclear equation one
Thanks.

bump

[pikachu975]

bump

Natural Radioactivity one - Transmutations that involve natural radioactivity include alpha, beta minus, and beta plus decay. These all involve the transmutation of one element into another. This change in binding energy due to a different element with differing amount of nucleons means that the extra energy is converted to mass via the energy mass equivalence. For example in beta minus decay, a neutron changes to a proton and an electron and anti-neutrino are released.

Nuclear Equation one - Energy is released as there is a difference in the binding energies between the left and right hand side of the equation. This difference in binding energy means the extra energy is released in the nuclear reactor, e.g. as heat to be used by the coolant to do work.

[itssona]

heyy do we need to know advantage/disadvantage of solid fuel/liquid fuel enginses in rockets

[blasonduo]

heyy do we need to know advantage/disadvantage of solid fuel/liquid fuel enginses in rockets

Are you referring the Goddard and the named scientist dot point? If so, Identify why solid fuel was insuffiecient for space exploration, what Goddard was able to do with oxygen and hydrogen, and how this improved space exploration and why it was significant. (able to explore further)

[itssona]

Are you referring the Goddard and the named scientist dot point? If so, Identify why solid fuel was insuffiecient for space exploration, what Goddard was able to do with oxygen and hydrogen, and how this improved space exploration and why it was significant. (able to explore further)

yes thank you so much!!

[sidzeman]

Hey regarding MRI in Med Phys,
I know that the application of a strong magnetic field causes protons to align with the direction of the mag field (parallel or anti parallel), and then later a radio pulse wave knocks them out of alignment.
However, where does the protons precessing in phase come in? Is that due to the strong magnetic field as well, or as a result of the radio pulse?

Also, how do the gradient coils ensure every voxel is unique?

[bsdfjnlkasn]

Hey there!

Could someone please explain to me why the maximum wavelength occurs when the energy of a photon = minimum energy required to eject an electron from a metal surface?

[sidzeman]

Hey there!

Could someone please explain to me why the maximum wavelength occurs when the energy of a photon = minimum energy required to eject an electron from a metal surface?

Energy of a photon is inversely proportional to its wavelength (E = hc/lamda) - meaning as wavelenght goes up total energy goes down.  Therefore it makes sense that max wavelength of a photon that can still cause emission is given by the min energy to eject the electron (work function) - with wavelength any higher, the energy of the photon would not be enough to eject the electron.

[jamonwindeyer]

Hey regarding MRI in Med Phys,
I know that the application of a strong magnetic field causes protons to align with the direction of the mag field (parallel or anti parallel), and then later a radio pulse wave knocks them out of alignment.
However, where does the protons precessing in phase come in? Is that due to the strong magnetic field as well, or as a result of the radio pulse?

Also, how do the gradient coils ensure every voxel is unique?

Hey! Basically, precession is just something nuclei do in a magnetic field. You don't really need to explain why. There is actually a formula for the precession frequency from the properties of the particle, and the applied magnetic field called the Larmor relationship:



But this isn't assessable -  You just need to know what precession is, really

As for unique voxels, picture every slice in the Z-direction assigned a number 1-255: We do this by varying the magnetic field strength at each point along the axis. Then, do the same for the X-Y directions. So then, each voxel is unique because there is a varying field strength in that direction. It becomes like a coordinate system, so (22,43,176) or (54,197,105) become specific points due to the differing fields in each direction

[Aaron12038488]

my school will likely select the pendulum experiment as our practical exam. I was wondering if someone could elaborate on their practical exam and how they went about it. E.g. Was a method provided and which you carried out? Or did u have to design and carry out your own.
Thx

[winstondarmawan]

Would appreciate clarification with the following:
11. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/22192872_1340184369440416_505939024_n.png?oh=951d4909cc99aaa481a3dab26b06e4c1&oe=59D3E216
Answer is B, but not sure how this makes sense. Since wavelength is inversely proportional to energy, don't all low wavelength photons have high energy?
12. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/22207574_1340181356107384_294692406_n.png?oh=c96794f9307d05aa00a60c4426ac77dc&oe=59D4C8C4
Answer is B, but I got A.
My method was:
F=qvBsin(theta)
F=ma
a=(qvBsin(theta))/m
Because from proton to alpha particle mass (electron mass is negligible) is doubling and so is charge, there would be no effect on the acceleration of the alpha particle. Can someone clarify this and explain why the answer is B?
21. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/22207213_1340181849440668_499896216_n.png?oh=b29ca888cccec63415bb04481f6a0762&oe=59D393E1
Solution: https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/22184809_1340181916107328_1024926263_n.png?oh=6b585ab564eb36b31536643abce2f1d0&oe=59D39E15
I don't remember learning the third point: Superconductors only transmit DC. Can someone please explain this?
27. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/22156703_1340182206107299_1451835380_n.png?oh=5f8f623e6e65c0da3a2a5b214d3b13d1&oe=59D3AD90
Solution: https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/22192973_1340182382773948_1424324833_n.png?oh=fe5852336b67e0da077f9b2559c0efa5&oe=59D3DD8F
Is it okay if from 10-40 minutes my gradient was a little sloped down (due to orbital decay)?
Can someone also give me a mark indication for the following question:
Explain how the adoption of AC as the dominant electricity supply benefits society in terms of the advantages of AC over DC. (6)
In the 18th century, Westinghouse triumphed over Edison for electrical distribution in Washington D.C, campaigning for the benefits over AC electricity over DC electricity. This is indicative of AC electricity's dominance over DC, greatly benefiting society as we know it today.
- AC electricity allowed for long distance transmission, through the use of transformers. Due to the large power losses associated with DC, power stations were created closer to the city, resulting in urban clutter. Transformers operate via Faraday's Law, which states that a conductor experiencing a change in magnetic flux will have an induced EMF. This is only achievable through AC, where oscillating charges produce a continuous change in flux. Transformers allow for the stepping-up of voltage, in turn reducing current due to the Law of Conservation of Energy (V1I1=V2I2), thus minimising power loss (Ploss=I^2R) and benefiting society through more efficient energy. Furthermore, this allowed power stations to be built further apart from major cities, reducing urban clutter and exposure of society to pollution.
- The use of AC and transformers had allowed for the use of a wide array of electronic devices, whilst minimising excessive cabling. If DC was used, a different supply cable would be required for each output. However through AC, simple transformers and rectifiers can be used to allow access to electrical devices such as TVs, phone chargers - all of which increase quality of life and benefit society immensely.
Quanta to Quarks:
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/22156994_1340194479439405_1611052904_n.png?oh=a50fb621978bb8f8b9290520cbb64c8f&oe=59D3CDE7
Part (ii).
Thanks in advance!