HSC Physics Marathon 2013-2015 Archive (1 Viewer)

[anomalousdecay]

re: HSC Physics Marathon Archive

I'm doing Astrophysics.

Fair enough with the maths background and stuff. I just thought Astrophysics would be too boring for me though.

 

[anomalousdecay]

re: HSC Physics Marathon Archive

========

A new follow up question:



It isn't directly related to the Physics syllabus but I think its rather interesting, but of course can be answered with HSC physics knowledge, just a bit of imagination.

I am guessing that the mass will stay constant, but due to the decrease in radius, the density and hence gravitational field produced would approach infinity.
Therefore, to move the object away from the black-hole, you would need an infinite amount of energy.

By the way, this could be a good question for you sy (and any others on this page):

Explain, using mathematical reasoning, why classical physics does not support the fact that light can escape a black hole.
Determine a reasoning as to why light can not escape a black hole, which contradicts classical physics.

 

[nightweaver066]

re: HSC Physics Marathon Archive

I think this thread is deviating a bit. To answer these questions, one has to know what a black hole is, which isn't taught in the HSC and isn't fair to those who want to participate but haven't got a clue what you guys are talking about or where to begin.

Question:
Explain the green glow observed near the anode when a high voltage is applied to a discharge tube and the importance of it having a low gas pressure. (3 marks)

 

[HeroicPandas]

re: HSC Physics Marathon Archive

Electron–positron annihilation!

 

[someth1ng]

re: HSC Physics Marathon Archive

I think this thread is deviating a bit. To answer these questions, one has to know what a black hole is, which isn't taught in the HSC and isn't fair to those who want to participate but haven't got a clue what you guys are talking about or where to begin.

Agreed. Please keep this thread strictly HSC related.

I don't mind if you guys make another thread for things that are non-HSC but keep this thread within the boundaries of the HSC syllabus.

 

[WeaselPowa]

re: HSC Physics Marathon Archive

I think this thread is deviating a bit. To answer these questions, one has to know what a black hole is, which isn't taught in the HSC and isn't fair to those who want to participate but haven't got a clue what you guys are talking about or where to begin.

Question:
Explain the green glow observed near the anode when a high voltage is applied to a discharge tube and the importance of it having a low gas pressure. (3 marks)

Having a lower gas pressure with a particular gas will result in a green glow near the anode (not sure if it is necessary to mention what gas). The lower the gas pressure, the lower the striations, meaning that the striations will begin to become unnoticeable as the percentage of gas pressure decreases.
A green glow is made possible by the high voltage applied to the cathode, where the electrons, when coming in contact with particular gases, will provide enough energy to result in this green glow.
Another purpose as to why it is important to have low gas pressure is so it prevents too many molecules obstructing the path of electrons to reach its way to the anode. By creating a near vacuum, it will significantly decrease the gas pressure so that molecules do not block the path of electrons, thus allowing for a green glow at the end of an anode.

 

[WeaselPowa]

re: HSC Physics Marathon Archive

Question:
Max Planck and Albert Einstein were both personally affected by the years during, between and leading up to the two World Wars. They also held 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)

 

[nightweaver066]

re: HSC Physics Marathon Archive

Having a lower gas pressure with a particular gas will result in a green glow near the anode (not sure if it is necessary to mention what gas). The lower the gas pressure, the lower the striations, meaning that the striations will begin to become unnoticeable as the percentage of gas pressure decreases.
A green glow is made possible by the high voltage applied to the cathode, where the electrons, when coming in contact with particular gases, will provide enough energy to result in this green glow.
Another purpose as to why it is important to have low gas pressure is so it prevents too many molecules obstructing the path of electrons to reach its way to the anode. By creating a near vacuum, it will significantly decrease the gas pressure so that molecules do not block the path of electrons, thus allowing for a green glow at the end of an anode.

Decent response . I wouldn't give it 3 marks though, maybe 2.

The key things i was looking out for were:
- low gas pressure allowing electrons to accelerate gaining KE (1 mark)
- collisions with air molecules transferring sufficient energy to them near the anode excites them, and when they de-excite, they release this energy in the form of EMR - what we see to be green light (2 marks)

 

[skillstriker]

re: HSC Physics Marathon Archive

Question:
Max Planck and Albert Einstein were both personally affected by the years during, between and leading up to the two World Wars. They also held 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)

Einstein: pacifist, promoted world peace - gave lectures around the world, when he moved to America he sent a letter to the US president convincing the gov't to start the Manhattan project --> this later led to the death of thousands of Japanese , he later regretted his decision however when he realised that the Germans weren't close to making nuclear bombs
Planck: nationalist, loyal to whatever the gov't was, one of the first of 93 german intellectuals to sign the document supporitng the role of germany in the war, he then dedicated his research to whatever the war required of him, wasn't amoral however (he did go to Adolf Hitler to stop his racial policies)
Overall, both Planck and Einstein were opposed to war/violence however Einstein was more opposed to the pressures of politics

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

Decent response . I wouldn't give it 3 marks though, maybe 2.

The key things i was looking out for were:
- low gas pressure allowing electrons to accelerate gaining KE (1 mark)
- collisions with air molecules transferring sufficient energy to them near the anode excites them, and when they de-excite, they release this energy in the form of EMR - what we see to be green light (2 marks)

The green glow around the anode at low pressure is not due to the relaxation of the gas molecules in the tube, it is due to the glass itself!

Question: (4 marks)

An electron travelling in an Easterly direction within the cathode ray of a TV set travels at a velocity of 0.1c. It is acted upon by Earths gravitational field and its magnetic field
The horizontal component of Earths magnetic field in the area is 50micro Tesla directed North East
Compare the magnetic force and the gravitational force on the electron

 

[skillstriker]

re: HSC Physics Marathon Archive

F = qvBsin(theta)
F = -1.602 x 10^-19 x 0.1 x 3 x 10^8 x 50 x 10^-6 x sin45
F = 1.70 x 10^-16 N into the page

F = mg
F = 9.8 x 9.11 x 10^-31
F = 8.93 x 10^-30 N down

both the magnetic and gravitational force are vector quantities
differences: force due to the magnetic field is greater, they are in different directions

 

[superSAIyan2]

re: HSC Physics Marathon Archive

^Would it be better to give a quantitiative comparison - i,e the 'magnetic force' is x times greater than the gravitational force

 

[WeaselPowa]

re: HSC Physics Marathon Archive

Decent response . I wouldn't give it 3 marks though, maybe 2.

The key things i was looking out for were:
- low gas pressure allowing electrons to accelerate gaining KE (1 mark)
- collisions with air molecules transferring sufficient energy to them near the anode excites them, and when they de-excite, they release this energy in the form of EMR - what we see to be green light (2 marks)

Oh thanks! My understanding of cathode rays just increased ^^

 

[bleakarcher]

re: HSC Physics Marathon Archive

Can someone mark my answer to this question: Scientists have tried to explain observations of black body radiation using classical wave theory then quantum theory. How does quantum theory satisfactorily explain BBR? (3 marks)

My answer: Classical wave theory predicted that as the wavelength of the EMR emitted by a BB decreased the intensity of the radiation indefinitely increased. However, experimental evidence suggested that there existed a wavelength at which intensity peaks. Quantum theory satisfactorily explains this with the quantisation of light, considering it as composed of discrete packets of energy (photons). It explains that BBR is not emitted as continuous waves of energy but in photons each containing equal amounts of energy given by E=hc/lambda where lambda denotes the wavelength of the emitted EMR.

Thanks.

 

[skillstriker]

re: HSC Physics Marathon Archive

Classical theory predicted that as the wavelength of radiation emitted by a black body decreased, the intensity increased to infinity. However, this violated the law of conservation of energy. The quantum theory was then proposed by Planck as a 'mathematical trick' to theoretically derive the BBR curve. He proposed that instead of radiation being absorbed and emitted as a continuous wave, the radiation emitted and absorbed by the walls of a black body cavity was quantised and existed as discrete packets of energy. This satisfactorily explained the BBR curve because the energy could only be absorbed/emitted if there was a change in quantum state. The formula E=hf shows that as the wavelength decreases i.e. frequency increases, the change in energy becomes larger --> these large changes in quantum state do not exist in atoms at normal temperatures. This explains that as wavelength --> 0, intensity --> 0. Also,some changes in quantum state are more probable than other --> explains peak radiation. + chuck in a diagram

 

[iBibah]

Classical theory predicted that as the wavelength of radiation emitted by a black body decreased, the intensity increased to infinity. However, this violated the law of conservation of energy. The quantum theory was then proposed by Planck as a 'mathematical trick' to theoretically derive the BBR curve. He proposed that instead of radiation being absorbed and emitted as a continuous wave, the radiation emitted and absorbed by the walls of a black body cavity was quantised and existed as discrete packets of energy. This satisfactorily explained the BBR curve because the energy could only be absorbed/emitted if there was a change in quantum state. The formula E=hf shows that as the wavelength decreases i.e. frequency increases, the change in energy becomes larger --> these large changes in quantum state do not exist in atoms at normal temperatures. This explains that as wavelength --> 0, intensity --> 0. Also,some changes in quantum state are more probable than other --> explains peak radiation. + chuck in a diagram

It's a 3-marker

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

F = qvBsin(theta)
F = -1.602 x 10^-19 x 0.1 x 3 x 10^8 x 50 x 10^-6 x sin45
F = 1.70 x 10^-16 N into the page

F = mg
F = 9.8 x 9.11 x 10^-31
F = 8.93 x 10^-30 N down

both the magnetic and gravitational force are vector quantities
differences: force due to the magnetic field is greater, they are in different directions

Give a quantitative comparison! Also, this is relativistic speeds, so mass dilation would occur (would be slight though)
Both forces should be in same direction also (I.e., down)

Question:
Outline Hertz' experiment with radio waves. Include a diagram, the results and his conclusion in your answer (5 marks)

 

[skillstriker]

re: HSC Physics Marathon Archive

why are both of the forces down? also, can you please show me how mass dilation affects the force? thank you!

- hertz tried to verify maxwell's predictions for electromagnetic waes
- he set up a coil of wire with a gap in it and connected it to a high voltage source (induction coil) to produce a spark across the gap
- he placed a similar secondary coil 1.5m away from the first coil and observed that a spark jumped across that gap as well (diagram)
- since the secondary coil was not attached to a power source, it must have received EMR (radio waves) from the transmitter
- he also showed that these waves could be reflected, refracted, diffracted, polarised + had speed of 3 x 10^ 8; showing their similarity to light

 

[someth1ng]

re: HSC Physics Marathon Archive

Einstein: pacifist, promoted world peace - gave lectures around the world, when he moved to America he sent a letter to the US president convincing the gov't to start the Manhattan project --> this later led to the death of thousands of Japanese , he later regretted his decision however when he realised that the Germans weren't close to making nuclear bombs
Planck: nationalist, loyal to whatever the gov't was, one of the first of 93 german intellectuals to sign the document supporitng the role of germany in the war, he then dedicated his research to whatever the war required of him, wasn't amoral however (he did go to Adolf Hitler to stop his racial policies)
Overall, both Planck and Einstein were opposed to war/violence however Einstein was more opposed to the pressures of politics

That's contradictory.

 

[Fizzy_Cyst]

re: HSC Physics Marathon Archive

why are both of the forces down? also, can you please show me how mass dilation affects the force? thank you!

- hertz tried to verify maxwell's predictions for electromagnetic waes
- he set up a coil of wire with a gap in it and connected it to a high voltage source (induction coil) to produce a spark across the gap
- he placed a similar secondary coil 1.5m away from the first coil and observed that a spark jumped across that gap as well (diagram)
- since the secondary coil was not attached to a power source, it must have received EMR (radio waves) from the transmitter
- he also showed that these waves could be reflected, refracted, diffracted, polarised + had speed of 3 x 10^ 8; showing their similarity to light

Where is your diagram! haha

Make sure you talk about the frequency of the signal in the transmitter and the received signal being the same, perhaps also outlining how he showed that they could be polarised, their speed etc..

Re previous question, both would be down due to weight force always being down and using the RHP rule, you will see that when you use the scenario given in the question, your palm faces upwards, indicating force on a negative charge would be down

Question:
During your study of the HSC course you were required to identify practising male and female Australian scientists, and the areas in which they are currently working and information about their research.
Outline a current practising male and female scientist, the areas in which they are working and what research they are currently undertaking.