HSC Physics Question Thread

[itssona]

Yep! Gradient would be \(\frac{I}{V}\), and by Ohm's Law resistance is \(\frac{V}{I}\), so take the reciprocal

If the IV characteristics of a resistance are non-linear that means it is non-ohmic, meaning it doesn't obey Ohm's Law in the simplest sense. You can do resistance as the tangent to the curve if you want to, but you'll never touch that in HSC Physics (because it isn't a Calculus course)

Ah makes sense, thank you Jamon

[winstondarmawan]

Hello! Just wanted to ask if semiconductors are useful on their own, or are they only useful when used together (p-n junctions) in applications? TIA

[jamonwindeyer]

Hello! Just wanted to ask if semiconductors are useful on their own, or are they only useful when used together (p-n junctions) in applications? TIA

Hey! Really only useful when doped to form p and n types - Intrinsic semiconductors aren't very useful by themselves

[Jyrgal]

Hello 

Can someone explain how solar cells work?

thanks!

[jamonwindeyer]

Hello 
Can someone explain how solar cells work?
thanks!

Hey! That's a big question, understanding how they work requires a solid understanding of semiconductors (if you need a refresher, try this guide)

Assuming you have that, this is basically how it works. We have a PN-junction with a depletion zone, and that sets up an electric field. Then, we have some light hitting the junction, and this cause the photoelectric emission of electrons. These electrons experience a force due to the electric field, and this pushes them through an external circuit!!

(If you need a refresher on the photoelectric effect, check this guide!)

Basically, understanding solar cells is a test of a heap of the knowledge you gain in Ideas to Implementation. Read the guides, make sure you have that background knowledge, and understanding solar cells will be a lot easier

[Jyrgal]

Hey! That's a big question, understanding how they work requires a solid understanding of semiconductors (if you need a refresher, try this guide)

Assuming you have that, this is basically how it works. We have a PN-junction with a depletion zone, and that sets up an electric field. Then, we have some light hitting the junction, and this cause the photoelectric emission of electrons. These electrons experience a force due to the electric field, and this pushes them through an external circuit!!

(If you need a refresher on the photoelectric effect, check this guide!)

Basically, understanding solar cells is a test of a heap of the knowledge you gain in Ideas to Implementation. Read the guides, make sure you have that background knowledge, and understanding solar cells will be a lot easier

Hey, thanks for answering!
I was just wondering, don't solar cells use the photovoltaic effect rather than the photoelectric effect? (should i mention this if a question asked about solar cells)
Another question, where exactly do the electrons get released from? From my understanding, electrons from the n-type semiconductor gets excited and jumps into the conduction band, creating a positive hole in the valence band. This will attract electrons from the p-type semiconductor which with the energy provided by attraction force will jump across the depletion zone and fill the n-type holes. However, my teacher says that the light knocks off electrons from within the depletion zone itself, and since there is an electric field with the positive side on the n-type, the electron will from to the n-type. If this is the case, how does the light ever reach the depletion zone to knock off electrons?

Sorry if its a bit of a long read, I have a slight interest in these type of stuff so I wanna have a good understanding  .
Thanks!

[jamonwindeyer]

Hey, thanks for answering!
I was just wondering, don't solar cells use the photovoltaic effect rather than the photoelectric effect? (should i mention this if a question asked about solar cells)

You are totally right! It is just that at this level the two terms are interchangeable - The two effects are the same, except in the photovoltaic effect, the electron isn't ejected but instead still contained within the material. You are okay to use either term, most HSC resources/marking schemes would just use the photoelectric effect so as to link to other bits of the syllabus

Another question, where exactly do the electrons get released from? From my understanding, electrons from the n-type semiconductor gets excited and jumps into the conduction band, creating a positive hole in the valence band. This will attract electrons from the p-type semiconductor which with the energy provided by attraction force will jump across the depletion zone and fill the n-type holes. However, my teacher says that the light knocks off electrons from within the depletion zone itself, and since there is an electric field with the positive side on the n-type, the electron will from to the n-type. If this is the case, how does the light ever reach the depletion zone to knock off electrons?

Hmm, both sound like sensible explanations to me!! It just sounds like you are going to an explanation based on energy levels, and your teacher is just being a little more abstract. The question of whether light reaches the depletion zone, you can really sort of extend to the N-type semiconductor too - Neither would be directly exposed in a solar cell. In practice, anti-reflective coatings are used to ensure the light is 'captured' and allowed to reach the semiconductors. Really, it will work wherever the electron is released

Sorry if its a bit of a long read, I have a slight interest in these type of stuff so I wanna have a good understanding  .
Thanks!

Don't be sorry! I was the same in the HSC, it is why I'm studying Electrical Engineering now

[beau77bro]

Hey so I'm kind of stuck at an impass. My teacher said we could do what ever option we wanted, but my head teacher has said we can't. She has said we r only doing medical in the trial because my teacher is pregnant and she might leave and the head only knows medical - but that still doesn't make sense because she wouldn't be teaching us Watever we choose in the first place... Anyway. I had cancer as a small child and I'm not very comfortable looking into radiotherapy and all that kind of medical stuff - which luckily won't be in the trial as we only cover first two dot points. But I'm still stuck with the decision of do I keep it for the HSC or do I do quanta - which I'm so interested in but I know it's quite difficult. I will have to learn some of medical for the trial anyway so I was wondering if I should just grit my teeth and do it, or if u guys think I could pull off quanta for the HSC? I do think I could dedicate time to it - and that will ultimately get me the results I need (ESP if it's interesting) but I do have to improve my English as well as carrying the immense load that is 4u maths Ahahha. Any and all advice is appreciated for this lil pickle.

[jakesilove]

Hey so I'm kind of stuck at an impass. My teacher said we could do what ever option we wanted, but my head teacher has said we can't. She has said we r only doing medical in the trial because my teacher is pregnant and she might leave and the head only knows medical - but that still doesn't make sense because she wouldn't be teaching us Watever we choose in the first place... Anyway. I had cancer as a small child and I'm not very comfortable looking into radiotherapy and all that kind of medical stuff - which luckily won't be in the trial as we only cover first two dot points. But I'm still stuck with the decision of do I keep it for the HSC or do I do quanta - which I'm so interested in but I know it's quite difficult. I will have to learn some of medical for the trial anyway so I was wondering if I should just grit my teeth and do it, or if u guys think I could pull off quanta for the HSC? I do think I could dedicate time to it - and that will ultimately get me the results I need (ESP if it's interesting) but I do have to improve my English as well as carrying the immense load that is 4u maths Ahahha. Any and all advice is appreciated for this lil pickle.

Hey man,

Really sorry to hear about your previous health issues. I'm especially sorry to hear that those issues impact your wellbeing now, I can only imagine how tough that must be.
Generally, I would always recommend just to grit your teeth and do what your school teaches you. You'll have more resources to rely on, you'll have the benefit of them marking you, and you'll have to put less work in.
That being said, I've never given that advice in a circumstance like this. If you think learning that content will affect your mental health, then you should absolutely be discussing with you head teacher the option of doing another topic. Surely they would understand. I think, basically, you need to balance up your various interests here, and decide what you'd rather put yourself through. Unfortunately, this isn't a decision we can really help you with. Like I said, I would generally recommend just doing Medical Physics, but there are clearly real and important factors that make this study difficult. So, I guess I've said as much as I can. Feel free to keep chatting about this here, though; happy to help out in any way this community allows.

[johnk21]

Hey so I'm kind of stuck at an impass. My teacher said we could do what ever option we wanted, but my head teacher has said we can't. She has said we r only doing medical in the trial because my teacher is pregnant and she might leave and the head only knows medical - but that still doesn't make sense because she wouldn't be teaching us Watever we choose in the first place... Anyway. I had cancer as a small child and I'm not very comfortable looking into radiotherapy and all that kind of medical stuff - which luckily won't be in the trial as we only cover first two dot points. But I'm still stuck with the decision of do I keep it for the HSC or do I do quanta - which I'm so interested in but I know it's quite difficult. I will have to learn some of medical for the trial anyway so I was wondering if I should just grit my teeth and do it, or if u guys think I could pull off quanta for the HSC? I do think I could dedicate time to it - and that will ultimately get me the results I need (ESP if it's interesting) but I do have to improve my English as well as carrying the immense load that is 4u maths Ahahha. Any and all advice is appreciated for this lil pickle.

Sorry to hear about what you have been through, it really sucks
I am doing medical physics atm and i see that it mostly if not ALL memorisation.
My opinion would be if only the first two points are in your trials, literally just look at hsc past papers and memorise the answer because in Medical Physics the questions they can ask are VERY limited. Then do whatever option you want to do for the hsc. Worst case scenario is you just memorise everything for medical physics for the hsc, which is easily completable within a week imo.

[beau77bro]

Sorry to hear about what you have been through, it really sucks
I am doing medical physics atm and i see that it mostly if not ALL memorisation.
My opinion would be if only the first two points are in your trials, literally just look at hsc past papers and memorise the answer because in Medical Physics the questions they can ask are VERY limited. Then do whatever option you want to do for the hsc. Worst case scenario is you just memorise everything for medical physics for the hsc, which is easily completable within a week imo.

Thanks johnk21, appreciate the advice and will do - worried because the option I wanna do is quanta though haha- but I appreciate the support and I'm very reassured by the simplicity of medical as you described - if it's half as easy as that it will make it a lot easier to study even when I don't wanna do it?

[jamonwindeyer]

Thanks johnk21, appreciate the advice and will do - worried because the option I wanna do is quanta though haha- but I appreciate the support and I'm very reassured by the simplicity of medical as you described - if it's half as easy as that it will make it a lot easier to study even when I don't wanna do it?

Medical is a very memorisation heavy option, a few tricky bits and pieces to really understand how the scanning methods all work -  I personally found Medical a really interesting Option myself though

Personally, your personal health aside, I'd recommend to do Medical. Purely to avoid double dipping. That said, you can absolutely learn Quanta yourself if you need to. Worst case, find a tutor who can spend a couple of weekends teaching it to you properly after you've learned Medical for your Trial.

You absolutely need to do what is best for you. If it puts your mind at ease, the way Medical is taught is very much Physics focused, as you'd imagine. The only relation to the human body is what sorts of afflictions each technique is good at spotting - Besides that, it is all on the science. Definitely no specific focus on the treatment and diagnosis end, it is more on how they work and a little bit of why you'd use one over the other

[Maraos]

Hey guys 
I've got a practical examination this Thursday (worth 20%  ) and I'm not really sure how i should prepare for it.

The notification is practically useless since the only information it gives is that the work covered involves 'all skills work as outlined by the syllabus'. My teacher wouldn't even tell us what topic the exam will be on 
This exam is different to my last 'skills' exam, which did not consist of a practical side to it. This exam will involve 20+ students partaking in pracs followed by questions etc. So I guess we are limited to only some pracs in the sense that 20 students will all have to do it.

Any advice, or ideas on what it could be would be greatly appreciated 

Thanks! 

[jamonwindeyer]

Hey guys 
I've got a practical examination this Thursday (worth 20%  ) and I'm not really sure how i should prepare for it.

Hey Maraos! Which topic is this for? Ideas to Implementation or?

[Maraos]

Hey Maraos! Which topic is this for? Ideas to Implementation or?

My teacher didn't specify, he won't even give us any hints haha.
So far my class has only done Motors/Generators, Ideas and Quanta. However my teacher did say that the prac will be on something we haven't done yet

Considering the entire class will need to do it I'm guessing it will have to involve a prac where alot of people can take part in it. So circuits? Motion pracs involving weights and retort stands?