Fizzycyst 2016 - HSC Physics Trial (1 Viewer)

[Glyde]

11. D for sure

 

[kashkow]

9. D depends on the time of flight or height

But the time of flight is equal for both of them? That's what I thought (hence my answer for B). Acceleration due to g is equal for both and the vertical velocity of both will be equal throughout the flight.

 

[jazz519]

I would put b for 9

 

[Glyde]

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

12 isn't the best question tbh but if you imagine the magnetic field as passing all the way through the disk, it's like it passes through the Infinetly thin surface areas from one side to the other, also note that larger coils (like in conducting lines) are thicker to reduce resistance, well the thicker disk will have less resistance and hence the eddy currents will be able to move more freely

 

[Glyde]

I would put b for 9

Assuming there is no air resistance then yeh it's b

 

[Glyde]

14 is d because the coils will be cutting the field on a more regular basis

 

[Glyde]

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

Which of the following would not increase the size of the deflection observed by the students?
(A) Increasing the number of turns in the secondary coil - the change in flux is greater , increasing deflection
(B) Increasing the voltage supply - again the change from 0 to 2v is greater then say 0 to 1v
(C) Decreasing the time taken to close the switch
(D) Increasing the size of the resistor- Best Answer: Use the V = I x R. If you have a power supply at a certain voltage, that won't change with adding more resistance. What will change is the current. For a set voltage (V), if resistance (R) goes up, current (I) has to come down to keep the equation balanced. So now the voltage is higher in the primary coil!

 

[kashkow]

14 is d because the coils will be cutting the field on a more regular basis

I still don't understand your reasoning. 14 D is increasing armatures which I don't see provide a constant torque. Unless you mean 14 A since you seem to be talking about increasing coils (which implies increasing the turns?)

Which of the following would not increase the size of the deflection observed by the students?
(A) Increasing the number of turns in the secondary coil - the change in flux is greater , increasing deflection
(B) Increasing the voltage supply - again the change from 0 to 2v is greater then say 0 to 1v
(C) Decreasing the time taken to close the switch
(D) Increasing the size of the resistor- Best Answer: Use the V = I x R. If you have a power supply at a certain voltage, that won't change with adding more resistance. What will change is the current. For a set voltage (V), if resistance (R) goes up, current (I) has to come down to keep the equation balanced. So now the voltage is higher in the primary coil!

A) This is an ideal transformer so the flux is already at a maximum and the change in flux doesn't increase. If you mean the voltage is greater then this means the current is decreased and deflection is not increased.

B) I understand this

C) I understand your reasoning but about the switch being binary and not affecting the deflection. But I don't see how it is a better answer than A or D yet...

D) Well I think I did think of V=IR but my original reasoning I think was something along the lines of realising that the voltage is being constant. Thus the transformer would be the same regardless of the resistor (in terms of results in the secondary coil).

However thinking about this from another angle as I was today, if you use Is/Ip = np/ns you will see current in the secondary coil actually decreases if the primary coil current decreases and thus the deflection is decreased.

Due to some seemingly contrasting results, (which was what I was trying to figure out today) I'm not sure which approach to take is better/right in this case, if either of them at all (I could be flawed in some area, but this is currently where my understanding lies).

Your reasoning for this makes sense and I understand it up until the point where you say the voltage is higher in the primary coil. "So now the voltage is higher in the primary coil!" How did you come to this conclusion? From my understanding this is wrong and so my reasoning continues the logic and shows that deflection decreases in the galvanometer (or stays the same). If you could explain you're reasoning a bit more on how you got your answer that would be much appreciated (I really want to understand this question and the answer)!



Also BUMP, I'm still wondering about what other people got for the answers for the MCQ (especially for ones that haven't been answered by others).

 

[pikachu975]

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).

Wouldn't 8 be b) because the 2m is heavier so it drops faster (air resistance makes the m drop slower)? Or do we assume there is no air resistance?

 

[Green Yoda]

Wouldn't 8 be b) because the 2m is heavier so it drops faster (air resistance makes the m drop slower)? Or do we assume there is no air resistance?

C, because in physics the theoretical model disregards air resistance. This is proven by Galileo, that any object regardless of mass in the same gravitational field will fall at the same time as objects will accelerate at the same rate 'g'.

 

[pikachu975]

C, because in physics the theoretical model disregards air resistance. This is proven by Galileo, that any object regardless of mass in the same gravitational field will fall at the same time as objects will accelerate at the same rate 'g'.

Yeah but the question doesn't say if there is air resistance, so it's weird. It can still accelerate at the same rate but air resistance makes it fall differently. Gonna have to ask Chris about it.

 

[InteGrand]

Yeah but the question doesn't say if there is air resistance, so it's weird. It can still accelerate at the same rate but air resistance makes it fall differently. Gonna have to ask Chris about it.

Basically with HSC Physics projectiles, they generally expect you to assume there's no air resistance unless explicitly stated otherwise.

 

[pikachu975]

Basically with HSC Physics projectiles, they generally expect you to assume there's no air resistance unless explicitly stated otherwise.

Oh ok thanks for clearing this up

 

[123ryoma12]

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).

I got D for question 5
http://imgur.com/eMe1xVR
Not sure if I'm correct, but for this question you need to know how to convert eV to Joule or vice versa.
I also assumed the distance from cathode to anode was 1m, so I'm probably wrong.