# Physics Predictions/Thoughts (1 Viewer)

#### TeheeCat

##### Active Member
Woah, you memorised his equation?? for schrodinger just know how he introduced quantum ideas and the shift from a deterministic view on subatomic interactions to a probabilistic view, it uncovered the probabilistic nature of quantum particles. Also, explain how his model was also an improvement of de Broglie’s, where he defined the electron waves as a probability density of finding a particular electron within a specific orbitals. I’d also mention the different s p d f orbitals if you do chemistry and explain their shapes. Also talk about his wavefunction and the ‘collapse’ of the significance of the collapse of a wavefunction in the probability of finding an electron within an orbital. If you can, also mention the work of Dirac in using Schrodinger‘s ideas coupled with special relativity to discover the existence of anti-particles, and the work of Heissenberg and his uncertainty principle, and how it further supported the probabilistic nature of quantum physics
Haha no no, I didn't word that right. I didn't memorise the actual equation, but rather the fact he derived an equation and what it was used for. Thank you so much btw, you've been very helpful to all of us in this thread.

#### ABBAS38

##### Member
I’d say that is reasonable as a modern measurement, in fact I was also thinking of using interferometry as a modern technique
Ye coz hertz in the end still found the speed of light and in my tutoring book methods similar to hertz which were practically the same was under the subheading of resonance and interferometry and also how the accuracy increased through the modern time as the frequency and wavelength measurements became more accurate and in turn the speed of light became more accurate (v=f times wavelength)

#### lplsz2000

##### New Member
Woah, you memorised his equation?? for schrodinger just know how he introduced quantum ideas and the shift from a deterministic view on subatomic interactions to a probabilistic view, it uncovered the probabilistic nature of quantum particles. Also, explain how his model was also an improvement of de Broglie’s, where he defined the electron waves as a probability density of finding a particular electron within a specific orbitals. I’d also mention the different s p d f orbitals if you do chemistry and explain their shapes. Also talk about his wavefunction and the significance of the collapse of a wavefunction in the probability of finding an electron within an orbital. If you can, also mention the work of Dirac in using Schrodinger‘s ideas coupled with special relativity to discover the existence of anti-particles, and the work of Heissenberg and his uncertainty principle, and how it further supported the probabilistic nature of quantum physics
Man, you are getting high band 6 for sure. You are incredible. May I ask to what degree should be learn about the astronomy way of measuring the speed of light. I was just going to mention that the person measure the time it takes for Jupiter's moon to be eclipsed by Jupiter and concluded that it take light 22 minutes to travel the diameter of Earth's orbit. And I noticed that different textbook has different revolution path of stars and the mass that differentiate them is different, is it a big deal? Which one should we stick to? Thanks in advance

#### Arrowshaft

##### Well-Known Member
Man, you are getting high band 6 for sure. You are incredible. May I ask to what degree should be learn about the astronomy way of measuring the speed of light. I was just going to mention that the person measure the time it takes for Jupiter's moon to be eclipsed by Jupiter and concluded that it take light 22 minutes to travel the diameter of Earth's orbit. And I noticed that different textbook has different revolution path of stars and the mass that differentiate them is different, is it a big deal? Which one should we stick to? Thanks in advance
For older measurements I’d mention the work of Galileo and how his assistant uncovered their lanterns and used a sand/water based clock to determine the time took for the travel, and I’d memorise another technique - you can use Ole Romer (like you said, to measure the successive appearances and disappearances of Jupiter’s moon Io). As for the modern measurements I’d mention James Bradley’s work on stellar abberration to determine the speed of light, Fizeau’s cog tooth experiment (or Foucalt’s improvement on his method by using rotating mirrors). Just memorising 2 from each in detail should be good enough!

#### Hscbuzman

##### Active Member
@Arrowshaft what about this one? I feel I can only ever get 8/9 when this man marks ahahaha

#### Attachments

• 2.7 MB Views: 31

#### Balajanovski

##### Member
@Arrowshaft what about this one? I feel I can only ever get 8/9 when this man marks ahahaha
Honestly, the difference between an 8 & 9 is how well you express scientific ideas, not your actual understandings of them.
Its pretty obvious that you understand your physics, but you do use terminology which is not strictly scientific.
Little things like calling Bohr's orbits "orbit states".
"Fall into the nucleus" could be more scientifically described as "orbital decay".

I know its petty, but from briefly skimming your answer and looking at the marker's feedback, this seems to be your problem.

#### Hscbuzman

##### Active Member
Honestly, the difference between an 8 & 9 is how well you express scientific ideas, not your actual understandings of them.
Its pretty obvious that you understand your physics, but you do use terminology which is not strictly scientific.
Little things like calling Bohr's orbits "orbit states".
"Fall into the nucleus" could be more scientifically described as "orbital decay".

I know its petty, but from briefly skimming your answer and looking at the marker's feedback, this seems to be your problem.
Okay thanks for the feedback

#### Arrowshaft

##### Well-Known Member
Also you seem to have gotten some information wrong, you say that 1 in 8000 alpha particles were deflected directly back, however it was 1 in 8000 that were deflected back at an obtuse angle (>90 degrees). You also said something along the lines of the “the light shun” its “shone”, just little things like that. Overall, its a solid response however, but I do think your slightly informal tendencies in writing occasionally may steer the marker away from giving you a 9, but most likely - I’d say, that would be a 9.

#### Arrowshaft

##### Well-Known Member
Another point, as @Balajanovski said, with orbital decay I’d explain as to why that happens. I would say, by Maxwell’s fourth equation (Ampere’s Circuitial Law), an accelerating charge (such as the electrons orbiting the nucleus, due to centripetal acceleration) will emit EMR, thus by the law of conservation of energy; the kinetic energy of the electrons will be lost causing them to spiral inward through orbital decay.

#### Balajanovski

##### Member
Just a dump on what I know about Planck's hypothesis. Could you verify if my understanding is correct @Arrowshaft?

Q: Describe how Planck's explanation of black body radiation changed the direction of scientific thinking in the early twentieth century. (3 marks)

Prior to Max Planck's hypothesis on the nature of black body radiation, the accepted model of light was Maxwell's continuous wave theory. However, Maxwell's theory was unable to account for the features of a black body curve. It predicted that vibrational modes of higher frequencies in cavity radiators were more likely than lower frequencies, which resulted in the predicted curve, according to Rayleigh-Jeans law, having no peak emission, and approaching infinite intensity at higher frequencies, violating the law of conservation of energy. This was known as the UV catastrophe. Physicists, such as Wien, attempted to account for the UV catastrophe through classical arguments, however essentially introduced arbitrary constants to fit a polynomial with no real underlying model.

Max Planck's hypothesis however had the extraordinary insight to approach the black body problem through a discrete, not continuous model. He modified Wien's law to remove the arbitrary constants and built a mathematical model with the underlying assumption that the atoms in the walls of a cavity radiator acted to transmit and receive only certain modes of oscillation based on their transitions between quantised thermal energy states. This resulted in the electromagnetic energy a black body could emit and receive being made up of discrete quanta E = hf.

Since most atoms in a black body would be at a given temperature, certain thermal energy transitions would be more likely than others, explaining the peak wavelength. The thermal energies required for atoms to undertake the large energy transitions required to release high frequency radiation were furthermore, very unlikely in the black bodies studied, explaining the UV catastrophe.

The immense success of Planck's quantised model in explained the black body curved hinted to physicists that there were shortcomings to the continuous, classical view of the world. Planck's hypothesis would go on to change the course of physics from the classical to the quantum, with his quantisation of electromagnetic energy being fully realised in Einstein's quantised photon model of light.

#### Arrowshaft

##### Well-Known Member
Just a dump on what I know about Planck's hypothesis. Could you verify if my understanding is correct @Arrowshaft?

Q: Describe how Planck's explanation of black body radiation changed the direction of scientific thinking in the early twentieth century. (3 marks)

Prior to Max Planck's hypothesis on the nature of black body radiation, the accepted model of light was Maxwell's continuous wave theory. However, Maxwell's theory was unable to account for the features of a black body curve. It predicted that vibrational modes of higher frequencies in cavity radiators were more likely than lower frequencies, which resulted in the predicted curve, according to Rayleigh-Jeans law, having no peak emission, and approaching infinite intensity at higher frequencies, violating the law of conservation of energy. This was known as the UV catastrophe. Physicists, such as Wien, attempted to account for the UV catastrophe through classical arguments, however essentially introduced arbitrary constants to fit a polynomial with no real underlying model.

Max Planck's hypothesis however had the extraordinary insight to approach the black body problem through a discrete, not continuous model. He modified Wien's law to remove the arbitrary constants and built a mathematical model with the underlying assumption that the atoms in the walls of a cavity radiator acted to transmit and receive only certain modes of oscillation based on their transitions between quantised thermal energy states. This resulted in the electromagnetic energy a black body could emit and receive being made up of discrete quanta E = hf.

Since most atoms in a black body would be at a given temperature, certain thermal energy transitions would be more likely than others, explaining the peak wavelength. The thermal energies required for atoms to undertake the large energy transitions required to release high frequency radiation were furthermore, very unlikely in the black bodies studied, explaining the UV catastrophe.

The immense success of Planck's quantised model in explained the black body curved hinted to physicists that there were shortcomings to the continuous, classical view of the world. Planck's hypothesis would go on to change the course of physics from the classical to the quantum, with his quantisation of electromagnetic energy being fully realised in Einstein's quantised photon model of light.
That’s a very thorough response, I loved your use of the idea of quantum oscillators (although I do think it is a tad overkill for high school physics). I’d also mention the similarity in both curves toward higher wavelengths but most importantly I’d define what a black body is, as, correct me if I am wrong, but you didn’t mention how blackbodies absorb all incident radiation. That being said, this is a definite 3/3.

#### Arrowshaft

##### Well-Known Member
Also, since you went super in depth, i’d also draw the comparison Planck made with standing waves to the vibrational modes, supporting quantisation

#### ABBAS38

##### Member
but lets be real that is too much for 3 marks and nesa wouldnt give that many lines either.
But never the less good depth on the topic and so a question with bigger marks, you would be totally fine!

#### Arrowshaft

##### Well-Known Member
but lets be real that is too much for 3 marks and nesa wouldnt give that many lines either
as i said, it is overkill, that would be the typical response for a 5+ marker from a state ranker haha.

#### ABBAS38

##### Member
as i said, it is overkill, that would be the typical response for a 5+ marker from a state ranker haha.
tru tru!

#### Hscbuzman

##### Active Member
Remember everyone, you can get extra writing booklets!

#### Arrowshaft

##### Well-Known Member
Hey guys, a question - for the applications of step up and step down transformers, how much detail have you gone to? Because I dont know whether it is worth memorising the structure of powerstations and use of pylons, etc. or just knowing the basic concept of stepping up voltage to reduce current and hence power loss by
$\bg_white P_{loss}=I^2R$

#### Hscbuzman

##### Active Member
Hey guys, a question - for the applications of step up and step down transformers, how much detail have you gone to? Because I dont know whether it is worth memorising the structure of powerstations and use of pylons, etc. or just knowing the basic concept of stepping up voltage to reduce current and hence power loss by
$\bg_white P_{loss}=I^2R$
Like i can't see more then 4 marks on that sort of question due to the fact it is now less important in this syllabus compared to the old one.

#### Skuxxgolfer

##### Member
Could someone clarify for me "why cathode rays were a mystery at the time/ an area of debate. Thanks

#### Arrowshaft

##### Well-Known Member
Could someone clarify for me "why cathode rays were a mystery at the time/ an area of debate. Thanks
In summary: cathode rays were argued to be either waves or particles.

Evidence for the particle nature:
- when a paddle wheel was placed inside an evacuated CRT, the paddle wheel spun - implying the cathode rays had momentum and thus mass.
- when cathode rays were passed through electric and magnetic fields, they deflected
- they travelled significantly slower than light.
- they left at right angles to the surface of the cathode

Evidence for wave nature:
- rectilinear propagation (deduced from the shadows produced from the rays, refer to the Maltese across experiment)
- they passed through thin metal foils without damaging them