HSC Physics Question Thread

[Spencerr]

'Describe Planck's contribution to the development of the atomic model and explain how his work was critical in allowing the development of the Bohr model' (4 marks)

Planck, in order to explain observations for black body radiation proposed that emr emitted or absorbed by black bodies occurred in discrete packets known as quanta which carried energy equivalent to E = hf. This was the foundation of a new type of physics called quantum physics that was later validated by Einstein in his application of it to explain the photoelectric effect.
Bohr used Planck's idea of quantised energy to develop his atomic model which extended upon rutherford's planetary model of electrons orbiting a central nuclues. Since energy was quantised and existed in discrete packets, that means the energy shells within the atom must also be quantised instead of occuring over a spectrum. This was Bohr's first postulate and a direct consequance of Planck's contribution. Bohr's second postulate was that when an electron jumped from a lower energy shell to a higher energy shell, it would need to absorb a photon of emr that had energy equivalent to E=hf and when an electron jumped from a higher to a lower energy level, it would release a photon with energy equal to E=hf. Bohr's third postulate regarding the quantisation of angular momentum was also a direct consequence of quantum physics but it has more to do with why the electrons are stable in teh orbits than Planck's impact. Therefore, Planck's contribution had a critical impact on the development of Bohr's atomic model.

[Spencerr]

I'm hoping a helpful student reading this will lend a hand with this question, neither Jake, Rui or myself studied Quanta to Quarks, help out a fellow peer! It will help you too!

Luckily I do q2q !

[jamonwindeyer]

Luckily I do q2q !

You are a legend!

[MysteryMarker]

'Describe Planck's contribution to the development of the atomic model and explain how his work was critical in allowing the development of the Bohr model' (4 marks)

Planck, in order to explain observations for black body radiation proposed that emr emitted or absorbed by black bodies occurred in discrete packets known as quanta which carried energy equivalent to E = hf. This was the foundation of a new type of physics called quantum physics that was later validated by Einstein in his application of it to explain the photoelectric effect.
Bohr used Planck's idea of quantised energy to develop his atomic model which extended upon rutherford's planetary model of electrons orbiting a central nuclues. Since energy was quantised and existed in discrete packets, that means the energy shells within the atom must also be quantised instead of occuring over a spectrum. This was Bohr's first postulate and a direct consequance of Planck's contribution. Bohr's second postulate was that when an electron jumped from a lower energy shell to a higher energy shell, it would need to absorb a photon of emr that had energy equivalent to E=hf and when an electron jumped from a higher to a lower energy level, it would release a photon with energy equal to E=hf. Bohr's third postulate regarding the quantisation of angular momentum was also a direct consequence of quantum physics but it has more to do with why the electrons are stable in teh orbits than Planck's impact. Therefore, Planck's contribution had a critical impact on the development of Bohr's atomic model.

Thanks man, that answer was mint as. Just got another one on the limitations of Bohr's model:

One of the limititations was that Bohr's model used a mixture of both 'classical' and 'quantum' physics. What is the classical part of Bohr's model?

[Spencerr]

Thanks man, that answer was mint as. Just got another one on the limitations of Bohr's model:

One of the limititations was that Bohr's model used a mixture of both 'classical' and 'quantum' physics. What is the classical part of Bohr's model?

In order to derive Balmer's empirical equation regarding the wavelengths of emr emitted when electrons move from a higher energy level to a lower energy level. whcih is the 1 /lamda = ....Bohr had to combine quantum physics mathematics and classical physics mathematics so it was not a purely quantum model itself. If you search up the mathematics for his derivation of the Rhydberg equation, he used classical physics formulas for KE and GPE and then combined it with his quantisation condition L = nh/ 2pi.
This limitation of Bohr's atomic model was solved by Heisenberg's matrix mechanics which was a purely quantum model that described the interactions of subatomic particles and their movements. Since it was purely quantum, matrix mechanics also solved the existence of hyperfine spectra lines, the zeeman effect, and accurately predicted wavelengths for larger atoms. This was Heisenberg's second contribution after his uncertainty principle

[Neutron]

'Describe Planck's contribution to the development of the atomic model and explain how his work was critical in allowing the development of the Bohr model' (4 marks)

Planck, in order to explain observations for black body radiation proposed that emr emitted or absorbed by black bodies occurred in discrete packets known as quanta which carried energy equivalent to E = hf. This was the foundation of a new type of physics called quantum physics that was later validated by Einstein in his application of it to explain the photoelectric effect.
Bohr used Planck's idea of quantised energy to develop his atomic model which extended upon rutherford's planetary model of electrons orbiting a central nuclues. Since energy was quantised and existed in discrete packets, that means the energy shells within the atom must also be quantised instead of occuring over a spectrum. This was Bohr's first postulate and a direct consequance of Planck's contribution. Bohr's second postulate was that when an electron jumped from a lower energy shell to a higher energy shell, it would need to absorb a photon of emr that had energy equivalent to E=hf and when an electron jumped from a higher to a lower energy level, it would release a photon with energy equal to E=hf. Bohr's third postulate regarding the quantisation of angular momentum was also a direct consequence of quantum physics but it has more to do with why the electrons are stable in teh orbits than Planck's impact. Therefore, Planck's contribution had a critical impact on the development of Bohr's atomic model.

Nice answer dude! It might also be a nice touch to include that by using Planck's quantisation theory within the Bohr model, the characteristic hydrogen emission spectra could be explained! (One of the primary experimental evidences for the Bohr model)

[Neutron]

Here's a bit of I2I to mix up the posts

I was wondering whether there's anything fundamentally wrong with my understanding about Planck and if one of you kind fellows could read my response to this question, that would be amazing

Describe the hypothesis proposed by Planck which resolved the problem with black body radiation (This was part 2 of a question, I already explained the UV catastrophe in the first part )

Planck's proposed the quantisation theory, which stated that energy is emitted and absorbed in discrete amounts given by E=hf. When an electron absorbs a discrete packet of energy, it will increase to a higher energy state before returning to its original energy state and re-emitting the photon of the specific energy. Therefore, in order for an electron to emit high frequency radiation, it must absorb the high frequency radiation first. However, the energy associated with such high frequency radiation is equal to or greater than the ionising energy. As such, the electron is liberated from the atom (ionised) before it can jump back down and emit the high frequency radiation. Thus, Planck was able to explain the lack of high frequency radiation emitted during blackbody radiation.

Thanks guys!

Neutron

[Spencerr]

Here's a bit of I2I to mix up the posts

I was wondering whether there's anything fundamentally wrong with my understanding about Planck and if one of you kind fellows could read my response to this question, that would be amazing

Describe the hypothesis proposed by Planck which resolved the problem with black body radiation (This was part 2 of a question, I already explained the UV catastrophe in the first part )

Planck's proposed the quantisation theory, which stated that energy is emitted and absorbed in discrete amounts given by E=hf. When an electron absorbs a discrete packet of energy, it will increase to a higher energy state before returning to its original energy state and re-emitting the photon of the specific energy. Therefore, in order for an electron to emit high frequency radiation, it must absorb the high frequency radiation first. However, the energy associated with such high frequency radiation is equal to or greater than the ionising energy. As such, the electron is liberated from the atom (ionised) before it can jump back down and emit the high frequency radiation. Thus, Planck was able to explain the lack of high frequency radiation emitted during blackbody radiation.

Thanks guys!

Neutron

Hey there, I have 3 responses.

Firstly, when planck proposed his quantisation theory, he didn't link it to electrons moving up or down energy levels, this was done much later. What Planck proposed was that the EMR packets were produced by atoms within the black body oscillating at certain discrete frequencies. The source of the EMR were atomic oscillations.

Secondly, the modern day kinda explanation for why the black body radiation curve peaks an then falls down to zero is that there aren't that many electrons making that huge fall from a very high energy level to a low energy level and producing that large frequency within the EMR photons (in a simplistic sense).
'
Thirdly, from what i understand, if a photon of emr hits an electron, if it has sufficient energy, it will propel the electron to the next energy shell or completely remove it. But if it does not have energy to move the electron to a higher stationary state/energy level, it will be absorbed and re-emitted.

This is the extent of what I know, I'd be interested if something else has a more comprehensive answer.

[jamonwindeyer]

Hey there, I have 3 responses.

Firstly, when planck proposed his quantisation theory, he didn't link it to electrons moving up or down energy levels, this was done much later. What Planck proposed was that the EMR packets were produced by atoms within the black body oscillating at certain discrete frequencies. The source of the EMR were atomic oscillations.

Secondly, the modern day kinda explanation for why the black body radiation curve peaks an then falls down to zero is that there aren't that many electrons making that huge fall from a very high energy level to a low energy level and producing that large frequency within the EMR photons (in a simplistic sense).
'
Thirdly, from what i understand, if a photon of emr hits an electron, if it has sufficient energy, it will propel the electron to the next energy shell or completely remove it. But if it does not have energy to move the electron to a higher stationary state/energy level, it will be absorbed and re-emitted.

This is the extent of what I know, I'd be interested if something else has a more comprehensive answer.

You are correct on all three counts, though the first response goes a little deeper I think, certainly deeper than HSC Physics requires  second response is perfect, the larger energy 'jumps' are just less common, which makes fundamental sense. And your third response is also spot on 

Here's a bit of I2I to mix up the posts
I was wondering whether there's anything fundamentally wrong with my understanding about Planck and if one of you kind fellows could read my response to this question, that would be amazing
Thanks guys!
Neutron

I think your response is great Neutron! I'd pull back a bit though, this is a Describe question after all, in an exam you'd only need roughly half of that word count to get the marks. Perhaps take out the details about ionising radiation and replace it with the more simplistic explanation suggested above, which is also a little more correct in this context 

[MysteryMarker]

For my homeboi diiiiiii - quanta to quarks

'Analyse the ability of the Rutherford-Bohr model to completely explain observed spectral characteristics' - 4 marks

To attain 4 marks two observations it could and could not explain must be analysed. I'm stuck on finding two observations it could analyse, i've found one being: The production of spectral lines due to the electrons in the atom jumping from one energy level to a lower energy level. What is another observation that it could explain?

Cheers.

[Spencerr]

For my homeboi diiiiiii - quanta to quarks

'Analyse the ability of the Rutherford-Bohr model to completely explain observed spectral characteristics' - 4 marks

To attain 4 marks two observations it could and could not explain must be analysed. I'm stuck on finding two observations it could analyse, i've found one being: The production of spectral lines due to the electrons in the atom jumping from one energy level to a lower energy level. What is another observation that it could explain?

Cheers.

The Rutherford model was the planetary model of random orbiting electrons. Bohr placed those electrons into discrete energy levels and shells and proposed that when an electron moves from a higher to a lower energy she'll,  it'll emit emr that correspond to the frequency of the spectra lines e =hf thus explaining the hydrogen spectrum.  Bohr used his atomic model to theoretically derive Balmer equation which was completely empirical based on the observations of the spectral line wavelengths thus bohrs model not only explained why the spectral lines were discrete but it also explained the exact wavelengths of those lines. Limitations include zee man effect, hyperfine lines relative intensity, and why it doesn't work for larger atoms. All these limitations exist because it's a simplistic conflation of quantum and classical physics

[conic curve]

Okay so I'm trying to answer a question and am struggling with it

1. A train of straight waves of frequency 4.0 MHz passing though soft tissue in the human body at 1540 ms^-1 crosses into bone where its speed is 4216 ms^-1. Calculate:

a. The wavelength of the waves in the soft tissue
b. The frequency of the waves in the bone
c. The wavelength of the waves in the bone
d. The relative index of the bone relative to the soft tissue

For a, I got 385m for b I got 1054m, for c I got 1054m and for d I am not sure how to do it 

Also how do you do Snell's law questions when it has a  temperature of some sort in it e.g. determine the speed of waves in the salt water if their speed in fresh water is 1493 ms^-1 at 25 degrees celcius (don't solve this for me, give me a hint)

Thanks

[m_woods]

Hi, I am struggling with the following question:

Two conductors labelled X and Y, are carrying currents of 10A and 20A as shown. The force experienced by conductor Y is F newtons (refer to diagram attached). The force experienced by conductor X would be:
(A) F ↑
(B) F ↓
(C) 2F ↑
(D) 2F ↓

The answer was (B) F ↓ but I put down (D) 2F. Could someone please explain why it is (B) not (D)

[RuiAce]

Hi, I am struggling with the following question:

Two conductors labelled X and Y, are carrying currents of 10A and 20A as shown. The force experienced by conductor Y is F newtons (refer to diagram attached). The force experienced by conductor X would be:
(A) F ↑
(B) F ↓
(C) 2F ↑
(D) 2F ↓

The answer was (B) F ↓ but I put down (D) 2F. Could someone please explain why it is (B) not (D)

The force experienced between the conductors is definitely equal to each other in magnitude.

The key thing to know is that all the current do is vary the force on BOTH wires. If you increase the current in just one wire, the force between BOTH wires increases.

This is because the force per metre is an attractive force. Wire X attracts wire Y, as does wire Y attract wire X. The fact that it's equal in magnitude and opposite in direction follows directly from Newton's Third Law of Motion - For every action an object causes, there exists an equal and opposite reaction being exerted onto the object.

Remember: The attractive (or repulsive where appropriate) force is the force BETWEEN two wires. The conductors are exerting the same force on each OTHER.

[FallonXay]

Hello,

Regarding the Idea to Implementation topic - Cathode Rays, how would I assess the validity of the experiments on the nature of cathode rays (i.e paddle wheel, Maltese cross, etc)?

thanks.