# Thread: Physics Exam Thoughts

1. ## Re: Physics Exam Thoughts

Originally Posted by Qw0pper0
Doesn't Cos60 = 1/2 so it was 5m/s?
They meant final answer was 8.66

2. ## Re: Physics Exam Thoughts

Anyone else do Medical Physics?

3. ## Re: Physics Exam Thoughts

Originally Posted by Qw0pper0
Doesn't Cos60 = 1/2 so it was 5m/s?
Oh sorry yeah it it

4. ## Re: Physics Exam Thoughts

Originally Posted by EngineeringHelp
Anyone else do Medical Physics?
Yeah i thought it was pretty good actually

5. ## Re: Physics Exam Thoughts

Anyone know what the band 5 cut off will be? Asking for a friend

6. ## Re: Physics Exam Thoughts

Originally Posted by blinkandyoullmissit
Yeah i thought it was pretty good actually
Why are different frequencies used for Sector (3.5MHz) and B (20MHz) scans?

Also, the polarity of P and Q? I got P as positive and Q as negative? Correct or nah?

7. ## Re: Physics Exam Thoughts

Originally Posted by EngineeringHelp
Why are different frequencies used for Sector (3.5MHz) and B (20MHz) scans?

Also, the polarity of P and Q? I got P as positive and Q as negative? Correct or nah?
I put that too but P is negative turns out since it said "circuit" hence positive charges come out of the positive terminal. If it was just a wire it'd be P but nah

8. ## Re: Physics Exam Thoughts

Originally Posted by EngineeringHelp
Why are different frequencies used for Sector (3.5MHz) and B (20MHz) scans?

Also, the polarity of P and Q? I got P as positive and Q as negative? Correct or nah?
I don't completely remember what P and Q were, but the current travels in a clockwise direction.

9. ## Re: Physics Exam Thoughts

Originally Posted by fluffchuck
I don't completely remember what P and Q were, but the current travels in a clockwise direction.
Yeah I thought it was a normal wire so positive charges build up at P but guess it's a circuit so positive charges go to negative (P).

10. ## Re: Physics Exam Thoughts

Originally Posted by EngineeringHelp
Why are different frequencies used for Sector (3.5MHz) and B (20MHz) scans?

Also, the polarity of P and Q? I got P as positive and Q as negative? Correct or nah?
3.5 is used cause it has less interaction with bodily tissue so is used as sector scans imaging e.g. Babies in a mothers womb. Lower energy sound waves interact less with tissue so can "reach" further into the body, but as a result has lower resolution.

20 is used in situations where less penetration is required eg eye scans or other small areas of the body. The higher energy sound waves interact more and thus give a higher resolution image. B (brightness) indicates the size/thickness of a particular layer.

11. ## Re: Physics Exam Thoughts

What did people say for 5, the MCQ about undoped silicon? Pretty sure the answer must have been D, the one that says equal numbers of positive holes and electrons move in opposite directions, but I said A, that more electrons move than positive holes, because there are both free electrons and valence electrons moving in undoped silicon

12. ## Re: Physics Exam Thoughts

Originally Posted by doggian
What did people say for 5, the MCQ about undoped silicon? Pretty sure the answer must have been D, the one that says equal numbers of positive holes and electrons move in opposite directions, but I said A, that more electrons move than positive holes, because there are both free electrons and valence electrons moving in undoped silicon
That question confused me a bit. I went with D... but I don't think there should even be any holes (or at least not too many) in undoped silicon? Since it isn't doped with Boron for example to create a p-type semiconductor?

13. ## Re: Physics Exam Thoughts

Originally Posted by silverdawn565
That question confused me a bit. I went with D... but I don't think there should even be any holes (or at least not too many) in undoped silicon? Since it isn't doped with Boron for example to create a p-type semiconductor?
There will still be holes in undoped semiconductors as long as an electron jumps from the valence to conduction band. The absence of that electron always leaves a hole behind in the valence band. I think once it's been doped, for example with a group 3 element then the majority of charge carriers will be holes over electrons.

14. ## Re: Physics Exam Thoughts

Originally Posted by doggian
What did people say for 5, the MCQ about undoped silicon? Pretty sure the answer must have been D, the one that says equal numbers of positive holes and electrons move in opposite directions, but I said A, that more electrons move than positive holes, because there are both free electrons and valence electrons moving in undoped silicon
It should be D because electrons and holes exist in pairs, so there are equal amounts of electrons and holes.

15. ## Re: Physics Exam Thoughts

Originally Posted by Sp3ctre
There will still be holes in undoped semiconductors as long as an electron leaves jumps from the valence to conduction band. The absence of that electron always leaves a hole behind in the valence band. I think once it's been doped, for example with a group 3 element then the majority of charge carriers will be holes over electrons.
Oh, true. Thanks.

Originally Posted by fluffchuck
It should be D because electrons and holes exist in pairs, so there are equal amounts of electrons and holes.
That makes sense.

16. ## Re: Physics Exam Thoughts

I'm sorry but what were they smoking for the copper skipping rope question

17. ## Re: Physics Exam Thoughts

Originally Posted by doggian
What did people say for 5, the MCQ about undoped silicon? Pretty sure the answer must have been D, the one that says equal numbers of positive holes and electrons move in opposite directions, but I said A, that more electrons move than positive holes, because there are both free electrons and valence electrons moving in undoped silicon
Yeah, I agree with this.

Say 2 electrons get excited from VB —> CB, so you have 2 free electrons in CB, 2 holes in VB, but only way those holes will move is if an electron moves into it, so you would have 2 electrons moving in VB also :/

For it only being Q5 tho, I think they would want D, I don’t know how I feel about that.

18. ## Re: Physics Exam Thoughts

Originally Posted by fluffchuck
It should be D because electrons and holes exist in pairs, so there are equal amounts of electrons and holes.
Free electrons and positive holes exist in pairs. But holes can only move by the movement of valence electrons, not free electrons

19. ## Re: Physics Exam Thoughts

Originally Posted by doggian
Free electrons and positive holes exist in pairs. But holes can only move by the movement of valence electrons, not free electrons
Yeah that means both free electrons and valence electrons exist so there is more

20. ## Re: Physics Exam Thoughts

paper is out now. Think I'm looking at anything between 80-85 raw depending on how its marked. Is that enough to get a B6? For the proj motion question (29b) I did it all right but I thought that the 10ms-1 was horizontal (idk how I misread it that bad) so my answer was off but my process was right, will I lose 1 or 2 marks?

21. ## Re: Physics Exam Thoughts

Originally Posted by camstu
paper is out now. Think I'm looking at anything between 80-85 raw depending on how its marked. Is that enough to get a B6? For the proj motion question (29b) I did it all right but I thought that the 10ms-1 was horizontal (idk how I misread it that bad) so my answer was off but my process was right, will I lose 1 or 2 marks?
Probably lost 1 mark out of 3 I guess since the rest was okay. Also 80-85 would be enough for a b6 I'm just guessing b6 cutoff might be 78-80.

22. ## Re: Physics Exam Thoughts

can you please upload the physics question paper 2017

24. ## Re: Physics Exam Thoughts

I guarantee you, as long as you put in e=mc2 somewhere in the exam, yous will have nothing to worry about.

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