HSC Physics Question Thread

[raymatar]

Does anyone have a resource with answers for papers between 2001 and 2007?

[blasonduo]

Does anyone have a resource with answers for papers between 2001 and 2007?

https://tianjara.net/hsc/notes/Phys_Past_Paper_Sol.pdf

This is the best one I've found

[raymatar]

https://tianjara.net/hsc/notes/Phys_Past_Paper_Sol.pdf

This is the best one I've found

w

Yeah that's the same one I have but it's missing some answers and medical physics responses. Thanks for the help though.

[beau77bro]

It's pretty convultued hey? By the last part I'm guessing you mean Repition Time and Echo Delay. For T1 Relaxtion they use a short Repition Time to match the short T1 they use. The repition time is the time elapsed between consecutive  pulse of input radio waves. The relaxtion of the M vector happens very quickly, leaving some 'free' radio waves to be absorbed. So, the extra radio waves will make the image appear brighter as it is a more 'active' area. Whereas T2 use a long Echo Delay Time to match the long T2 in use. Echo time delay is the time delay betwee the emission of radio waves and measurement of those which return first. So in T2 images, the signals from the T2 relaxtion are measured after the initial radio waves are sent out which results in tissues with only long T2 contributing to the returning signals. Also, in T1 images, the Echo Delay Time is short so as to suppress any T2 and likewise, a long Repition Time is used in T2 images to suppress any T1. Hope that makes sense? 

VERY NICELY PUT (I FEEL) - GONNA NEED TO READ OVER A BIT AND A COUPLE TIMES. THANKYOU. anyone else wants to add anything greatly appreciated.

[Baylsskool]

Can anyone explain why black bodies actually have peaks, i mean theoretically it would work if the curve was exponentially decreasing but that's not what Planck discovered, why is there a section of energy missing at the start, why does the body not emit large amounts of energy due to the lower wavelengths being given off?? Is there an explanation for this missing gap?

I mean with the ultraviolet catastrophe,why can't there be an infinite source of energy for an infinitly small wavelength, cause it checks out mathematically, we just havnt discovered any frequencies higher than gamma, of course it can't be infinite but surely there's more to discover so how can the peak wavelength be so?? Shouldn't it technically, if we did find the smallest wavelength possible at least hit the wall of the graph and decrease from there???

Or advise someone I can talk to about this?

[mary123987]

Hey guys was just doing question 24 b and i am confused as to why the force isnt negative as when i subbed it in to F=qV/d i got -4.005 x 10 ^-14 (only thing that hints it out is part c) where you have to find velocity and considering eventually you have to squareroot it doesnt make sense to have a negative well its impossible!)
 also q 25 b) is it sufficient to use Vp/Vs = Is/Ip and say the info is incorrect as Vp/Vs ≠Is/Ip?
thankyou

[winstondarmawan]

Thank you for your response!
I'm just wondering why the eddy currents on R are negligible. I've always learnt that they had an impact on these types of questions, because even thought they are significantly smaller than the looped current produced in Q, they are still there.

Bumpp

[mary123987]

Can anyone explain why black bodies actually have peaks, i mean theoretically it would work if the curve was exponentially decreasing but that's not what Planck discovered, why is there a section of energy missing at the start, why does the body not emit large amounts of energy due to the lower wavelengths being given off?? Is there an explanation for this missing gap?

I mean with the ultraviolet catastrophe,why can't there be an infinite source of energy for an infinitly small wavelength, cause it checks out mathematically, we just havnt discovered any frequencies higher than gamma, of course it can't be infinite but surely there's more to discover so how can the peak wavelength be so?? Shouldn't it technically, if we did find the smallest wavelength possible at least hit the wall of the graph and decrease from there???

Or advise someone I can talk to about this?

Hey so just to give you a quick explanation the initial curve as indicated by classical theorty suggested that as wavelength decreased radiance/intensity would increase to infinity now classical theory was wrong as firstly evidence showed otherwise and secondly thus increase in energy would violate the principle of consevation of energy as energy is supposedly being created without anthing causing it !
Also from my understanding there is no actual section of energy missing in the beginning .
I get that your confused about why there can't be an infinite source of energy for an infinitly small wavelength but the reason is radiation emitted and absorbed by the walls of a black body cavity is quantised meaning the energy of photons is related to the frequency and thus in accordance to Einstein's contribution there is a threshold frquency , even if a light is very bright and carries large energy .
So whilst E=hf (which equals E= hc/λ)suggests that there can be an infinite source of energy for an infinitly small wavelength Einstein said nope actually there is a threshold frquency and this theory was discovered based on experimental data thus the reason for the peak .
Hope it makes sense

[jamonwindeyer]

VERY NICELY PUT (I FEEL) - GONNA NEED TO READ OVER A BIT AND A COUPLE TIMES. THANKYOU. anyone else wants to add anything greatly appreciated.

Keep in mind that the data can be localised because the magnetic field is slightly different in every voxel, as set up by the gradient coils - So we can use this to figure out where our readings are coming from

I can't possibly comprehend how complex these algorithms must be to reconstruct these images, crazy stuff!

Thank you for your response!
I'm just wondering why the eddy currents on R are negligible. I've always learnt that they had an impact on these types of questions, because even thought they are significantly smaller than the looped current produced in Q, they are still there.

I mean you could just as easily say that there are eddy currents in the plastic - But again, they are significantly smaller than the looped current produced in Q so I suppose we are comparing insignificants, and the Excel book has chosen to ignore the difference. There probably would be one, but it would be tiny - Both would behave essentially as they normally would under gravity

[mary123987]

Bumpp

Hey Although the charge in R experiences a force the break in the copper ring ,the emf established  does not have a complete circuit so current cant flow so it lands at the same time as the plastic ring as nothing is opposing its downward force thus it accelerated down at the same rate as the pastic one

[jamonwindeyer]

Hey guys was just doing question 24 b and i am confused as to why the force isnt negative as when i subbed it in to F=qV/d i got -4.005 x 10 ^-14 (only thing that hints it out is part c) where you have to find velocity and considering eventually you have to squareroot it doesnt make sense to have a negative well its impossible!)
 also q 25 b) is it sufficient to use Vp/Vs = Is/Ip and say the info is incorrect as Vp/Vs ≠Is/Ip?
thankyou

Hey! Which paper is this from? I think I know these questions though sooo:

- When you find force, you can ignore the negative in \(q\) because it only affects the direction. So instead of \(-0.00004nN\) (your answer), you just write \(0.00004nN\) down, or up, or however you define the negative direction. You ignore any negatives in the formula itself

- Definitely okay, but it is better to examine it in terms of the conservation of energy. If you compare \(V_pI_p\) to \(V_sI_s\), you'll find that you've created energy in the secondary coils, seemingly from nothing -> Output power is higher than input! If my memory of this question serves me right, at least

[mary123987]

WOOPS !! sorry i forgot to insert the link 2015 https://www.boardofstudies.nsw.edu.au/hsc_exams/2015/exams/2015-hsc-physics.pdf
yes your right  power in the first one is 0.12 whilst in  the second  0.2 that makes sense thanks for that your a legend

[winstondarmawan]

How would one go about assessing the reliability, validity and accuracy of second hand sources?

[jamonwindeyer]

How would one go about assessing the reliability, validity and accuracy of second hand sources?

A reliable source will match with other sources when cross checked, a valid source will be free from bias (was it written by someone from the Flat Earth Society, for example?) and an accurate source will have data and information that matches known fact

[winstondarmawan]

I mean you could just as easily say that there are eddy currents in the plastic - But again, they are significantly smaller than the looped current produced in Q so I suppose we are comparing insignificants, and the Excel book has chosen to ignore the difference. There probably would be one, but it would be tiny - Both would behave essentially as they normally would under gravity

Hey Although the charge in R experiences a force the break in the copper ring ,the emf established  does not have a complete circuit so current cant flow so it lands at the same time as the plastic ring as nothing is opposing its downward force thus it accelerated down at the same rate as the pastic one

Thank you! What about the case of slits in a metal sheet, the eddy currents are somewhat significant there right?
So now it is my understanding that rings require the entirety of the ring for a significant current to flow whereas sheets and cubes (e.g. transformers) can have slits. Would this be correct?