Fizzycyst 2016 - HSC Physics Trial (2 Viewers)

[Fizzy_Cyst]

Hey guys,

Find attached the core section of the Physics Trial which my tutoring students sat last week

No answers attached

If you want to discuss answers, by all means I will contribute to that discussion

 

[Speed6]

Anything for chemistry?

 

[ze-]

Any explanation for Q12? Does thickness affect mass? Therefore, the thicker disc will have greater angular momentum. So it will be harder to stop?

 

[123ryoma12]

Any explanation for Q12? Does thickness affect mass? Therefore, the thicker disc will have greater angular momentum. So it will be harder to stop?

The question is probably more about the induced eddy current.
So answer is C

 

[ze-]

The question is probably more about the induced eddy current.
So answer is C

Does the thickness of the disc even affect the rate of change of flux? Aren't the magnets cutting the same surface area on both discs? Sorry, I don't really understand haha

 

[123ryoma12]

Does the thickness of the disc even affect the rate of change of flux? Aren't the magnets cutting the same surface area on both discs? Sorry, I don't really understand haha

Magnetic fields can only be blocked by superconductors (Meissner effect).
So in this case, the magnetic field permeates the whole disc thus more/larger induced eddy currents.

Edit: Another example where magnetic field lines permeates a whole object is with the soft iron cores in transformer thus the need for lamination to induce much smaller eddy current.

 

[indecisive101]

Magnetic fields can only be blocked by superconductors (Meissner effect).
So in this case, the magnetic field permeates the whole disc thus more/larger induced eddy currents.

Edit: Another example where magnetic field lines permeates a whole object is with the soft iron cores in transformer thus the need for lamination to induce much smaller eddy current.

Is the answer for Q30
a. E=5.46 x 10^4 N C^-1
b. v = 6.3 X 10^-19 m/s

 

[123ryoma12]

Is the answer for Q30
a. E=5.46 x 10^4 N C^-1
b. v = 6.3 X 10^-19 m/s

http://i.imgur.com/H0IuppH.png
This is my attempt. I might not be right but i'm 100 percent sure your (b) is wrong because it's too slow.

 

[jazz519]

http://i.imgur.com/H0IuppH.png
This is my attempt. I might not be right but i'm 100 percent sure your (b) is wrong because it's too slow.

Hey I think u made a calculation error in the v = root(2as) bit cause you should get the same as this https://postimg.org/image/llhp4r42z/

 

[123ryoma12]

Hey I think u made a calculation error in the v = root(2as) bit cause you should get the same as this https://postimg.org/image/llhp4r42z/

Ye, yours is definitely correct.
Idk what's wrong with mine though :L

 

[jazz519]

Ye, yours is definitely correct.
Idk what's wrong with mine though :L

I think you just subbed in values wrong for that part cause I subbed in ur values to test that and I got the 2.5....x10^6, which was same as mine

 

[123ryoma12]

I think you just subbed in values wrong for that part cause I subbed in ur values to test that and I got the 2.5....x10^6, which was same as mine

Oh :< I see what I did wrong =,=.
I did 0.375^-2 instead of 0.375 x 10^-2

 

[indecisive101]

Thanks! Lol completely misinterpreted question. I just assumed acceleration was 9.8. Didn't realise projectile motion was involved here as well. Really good question, thanks for posting it!

 

[kashkow]

Does anyone have answers for the multiple choice section just so I can compare?

Mine were:

1. A
2. B
3. D
4. A
5. Not even sure for this one
6. D
7. There was no Q7.
8. C
9. B
10. B
11. C
12. A?
13. C
14. A or B?
15. C
16. A or D?
17. B
18. A
19. C
20. B

I could be wrong about most of 'em but meh. Ones with 2 options I couldn't decide between them as they both seemed right and for 12 I had read this thread and the answer was said to be C, but I wasn't sure about that due to my current and perhaps incomplete understanding of flux. Would like to discuss this one (and any others I get wrong).

 

[kashkow]

Does anyone have answers for the multiple choice section just so I can compare?

Mine were:

1. A
2. B
3. D
4. A
5. Not even sure for this one
6. D
7. There was no Q7.
8. C
9. B
10. B
11. C
12. A?
13. C
14. A or B?
15. C
16. A or D?
17. B
18. A
19. C
20. B

I could be wrong about most of 'em but meh. Ones with 2 options I couldn't decide between them as they both seemed right and for 12 I had read this thread and the answer was said to be C, but I wasn't sure about that due to my current and perhaps incomplete understanding of flux. Would like to discuss this one (and any others I get wrong).

LOL, just realised 15 is wrong as it's an electron. Should be D.

 

[Glyde]

12- I'd say C because laminations in iron cores are sometimes perpendicular to the magnetic field direction, meaning a greater thickness must have some effect on the spin. I assume a larger area will allow more eddy currents to 'fit' reducing the change

14- definitely D, when there is one armature there will be a moment where the coil does not cut any field lines. Usually we'd create a radial magnetic field to keep the torque constant however since this is not an option we increase the number of loops.

16- C, since the switch can either be on or off (like binary , 1 or 0 ) there are no midpoints thus the speed in which you go from on to off will always be the same, instantaneous

 

[Glyde]

Does anyone have answers for the multiple choice section just so I can compare?

Mine were:

1. A
2. B
3. D
4. A
5. Not even sure for this one
6. D
7. There was no Q7.
8. C
9. B
10. B
11. C
12. A?
13. C
14. A or B?
15. C
16. A or D?
17. B
18. A
19. C
20. B

I could be wrong about most of 'em but meh. Ones with 2 options I couldn't decide between them as they both seemed right and for 12 I had read this thread and the answer was said to be C, but I wasn't sure about that due to my current and perhaps incomplete understanding of flux. Would like to discuss this one (and any others I get wrong).

2.A
btw Gravity IS a centripetal force and is the only force acting on a safelight as it is constantly falling

 

[kashkow]

2.A
btw Gravity IS a centripetal force and is the only force acting on a safelight as it is constantly falling

Oh yeah lol I must have forgot that somehow or my understanding wasn't fully complete here.

 

[Glyde]

9. D depends on the time of flight or height

 

[kashkow]

12- I'd say C because laminations in iron cores are sometimes perpendicular to the magnetic field direction, meaning a greater thickness must have some effect on the spin. I assume a larger area will allow more eddy currents to 'fit' reducing the change

14- definitely D, when there is one armature there will be a moment where the coil does not cut any field lines. Usually we'd create a radial magnetic field to keep the torque constant however since this is not an option we increase the number of loops.

16- C, since the switch can either be on or off (like binary , 1 or 0 ) there are no midpoints thus the speed in which you go from on to off will always be the same, instantaneous

12- here I'm more interested about flux as the induced emf will be dependent on the flux. Does thickness increase flux? You're statement "I assume a larger area will allow more " doesn't really apply since the area of the disc experiencing flux is the same in both discs.

14. I'm confused on your response. Did you make a typo with D?

16. This makes sense but the other two options I made also make sense to me. Why are they wrong?

Cheers for your answers btw, really appreciate it