HSC Physics: Suggested Answers and Discussion

[synix]

Just wondering if u guys plan on answering any of the options topics? Thnx

[jamonwindeyer]

Time of flight is irrelevant here. The elevator is still moving up BUT slowing down, the ball is NOT slowing down along with the elevator. Because the ball isn't slowing down it'd actually move up relative to the elevator which is slowing down. Hence the dotted line above the solid line.

You are totally right, but time of flight is one relevant way to explain the phenomenon. It IS in the air for longer after all

Imagine you are in an elevator, when you first take off from the ground, you experience a stronger downwards 'gravity'- just like a rocket ship taking off, this would cause the path shown in A. Just as you decelerate when you reach the top, imagine you are in the elevator, you get the fluttering feeling in the stomach, this is due to the feeling of lowered 'gravity', or a lower perceived weight. This lower weight means the flight will be longer. Pretty confident on this one. As for 15, I found this one hard... I think it should be A, I agree with the solutions, after lots of last minute research last night- light strikes the n or p type semiconductor around the boundary, creates the electron, hole pair (by exciting the electron out of the valence band), then the pn junction local electrical field pulls the electron towards the n type and the hole towards the p type. The light isn't changing the voltage, it is simply facilitating the electric field of the depletion zone achieving this.

Couldn't have said it better myself!

[gabe.ralph]

Imagine you are in an elevator, when you first take off from the ground, you experience a stronger downwards 'gravity'- just like a rocket ship taking off, this would cause the path shown in A. Just as you decelerate when you reach the top, imagine you are in the elevator, you get the fluttering feeling in the stomach, this is due to the feeling of lowered 'gravity', or a lower perceived weight. This lower weight means the flight will be longer. Pretty confident on this one. As for 15, I found this one hard... I think it should be A, I agree with the solutions, after lots of last minute research last night- light strikes the n or p type semiconductor around the boundary, creates the electron, hole pair (by exciting the electron out of the valence band), then the pn junction local electrical field pulls the electron towards the n type and the hole towards the p type. The light isn't changing the voltage, it is simply facilitating the electric field of the depletion zone achieving this.

But in doing so it creates a potential difference, so why not c). It just seems in a solar cell the potential difference is more important than the pairs. If both happen why is only A the answer.

[stateofmind]

Time of flight is irrelevant here. The elevator is still moving up BUT slowing down, the ball is NOT slowing down along with the elevator. Because the ball isn't slowing down it'd actually move up relative to the elevator which is slowing down. Hence the dotted line above the solid line.

a=(v-u)/t. so as acceleration is increasing, time of flight decreases. range=velocity x time. so less time equals less range
thats what I thought lol made an account just to post this

[bohimei]

Time of flight does change but by "irrelevant" I meant it wasn't needed for the question

[Cindy2k16]

hm my thoughts:
1. the multiple choice was hard. since im dumb i didnt know if voltage is stepped up or down for q1 but i guessed it right i think. Also the circular motion question freaked me out and I didn't know how to do it and did some weird calculations and still managed to get 5.9?? Also yep. fell for the speaker question and chose the wrong answer.

2. sigh. i shouldn't have looked at the answers. I told myself not to but then i did and I definitely regret it. The strangest thing was that I did the same working out for 30.a) as shown. but i didn't get that number..... I got a different value :/ so I must've done it wrong somehow....I probably would've been better off not knowing the answer (since I didn't even know if I did the question right but now I know i did it right but managed to get the wrong answer still) I didn't look at all the answers though, just some and then told myself to stop lol

3. I initially thought it was an alright exam. but the answers kind of gave me a reality check haha. I didn't see many mistakes out of the answers I glimpsed, but my mind tends to focus on what I did wrong rather than what I did right though :/

4. So for this exam I'm gonna go by my life motto of "expect the worst" 

Edit: Last MC question...I'm an idiot I was totally blind and only saw that the power supply was connected to the coil, and didn't see the coils on either side. Got that wrong. So 18/20 for MC... Not that bad though I really would've liked the safety of only losing marks in the long response (which i refuse to look at any more lol i only looked at the last question)

[jamonwindeyer]

Just wondering if u guys plan on answering any of the options topics? Thnx

I've started Medical Physics and I'll probably finish it later tonight; I'll have a crack at Age of Silicon too (I've done enough at uni to feel semi-confident, and you guys can check me). We might have some for Astrophysics at some point too.

If anyone would like to share their solutions for Geophysics or Quanta, PM me! I'll pop your answers in the post above and credit your username (gotta love that AN fame)

[jamonwindeyer]

But in doing so it creates a potential difference, so why not c). It just seems in a solar cell the potential difference is more important than the pairs. If both happen why is only A the answer.

The formation of the electron-hole pair by a photon doesn't affect the potential difference; that's a property of the junction. The electric field is relatively constant. The light frees an electron hole pair which can THEN be affected by the field

[ParallelPlatypus]

I agree, that is why I find this one hard (regarding Q15), but as for the most correct, is the light independently responsible for the creation of the voltage? No. It is the electric field that produces the voltage. What I mean to say, is some random bit of light could strike a p type semiconductor, and an electron - anti electron pair would form and then recombine- there would be no voltage. Hence it is not the light causing the voltage, but the electric field across the p n junction that already exists though. That is my take on it though... tough one.

[jamonwindeyer]

hm my thoughts:
1. the multiple choice was hard. since im dumb i didnt know if voltage is stepped up or down for q1 but i guessed it right i think. Also the circular motion question freaked me out and I didn't know how to do it and did some weird calculations and still managed to get 5.9?? Also yep. fell for the speaker question and chose the wrong answer.

Speaker question got me too; we can despair together sounds like you did great on the whole in a hard section!

2. sigh. i shouldn't have looked at the answers. I told myself not to but then i did and I definitely regret it. The strangest thing was that I did the same working out for 30.a) as shown. but i didn't get that number..... I got a different value :/ so I must've done it wrong somehow....I probably would've been better off not knowing the answer (since I didn't even know if I did the question right but now I know i did it right but managed to get the wrong answer still) I didn't look at all the answers though, just some and then told myself to stop lol

You'll get 2/3 just for the working, don't let it stress you!

3. I initially thought it was an alright exam. but the answers kind of gave me a reality check haha. I didn't see many mistakes out of the answers I glimpsed, but my mind tends to focus on what I did wrong rather than what I did right though :/

4. So for this exam I'm gonna go by my life motto of "expect the worst" 

You will be fine; this was a tough exam and it sounds like you did really well on the whole. Don't stress, it's done now, just party!

[jamonwindeyer]

I agree, that is why I find this one hard (regarding Q15), but as for the most correct, is the light independently responsible for the creation of the voltage? No. It is the electric field that produces the voltage. What I mean to say, is some random bit of light could strike a p type semiconductor, and an electron - anti electron pair would form and then recombine- there would be no voltage. Hence it is not the light causing the voltage, but the electric field across the p n junction that already exists though. That is my take on it though... tough one.

You need to be a tutor next year Platypus; you explain stuff really well, thanks heaps for your help!!

[bohimei]

"semi-confident"
that pun got me good

[ParallelPlatypus]

Thanks And no problem

[Cindy2k16]

So judging by the little information offered by the raw marks database.....is a raw mark of say, 85% for this exam going to award a band 6? Lower? Higher?

[Alalamc]

17/20 FOR MULTIPLE CHOICE AND LEGIT ONLY STUDIED 2 1/2 DAYS.. Award plz 😂