Section I - Multiple Choice (5 Viewers)

[oh well]

GAWD.. dat force question and. the cooktop.. so sad.... OUR BRAIN BEEN MINDFKED

+1

 

[someth1ng]

Here is my MC answers:
1. D
2. A
3. C
4. B
5. C
6. C
7. B
8. A
9. B
10. D
11. C
12. A
13. B
14. D
15. D
16. C
17. B
18. C
19. D
20. A

Q19: I actually believe that it should be C - low electrical resistance.
Q20: To said to detect thermal radiation, this means that you use the wavelength that will allow the most radiation to be detected. Using one that is a peak means that less light is detected and hence, less sensitive and hence, less suitable.

 

[kastle]

I had a problem with the Transformers Question, I can't remember which question number it was. I remember that it needed to step down a voltage from 20 to 2 so you needed the fraction of 2/20 or 1/10. So therefore the Primary coil needed to be greater than the secondary coil, Which ruled out A, and D. B was 20 and 3 and C was 20 and 10. Which don't fit either.

Can someone explain where my logic took a turn.

 

[mickstarify]

Here is my MC answers:
1. D
2. A
3. C
4. B
5. C
6. C
7. B
8. A
9. B
10. D
11. C
12. A
13. B
14. D
15. D
16. C
17. B
18. C
19. D
20. A

To said to detect thermal radiation, this means that you use the wavelength that will allow the most radiation to be detected. Using one that is a peak means that less light is detected and hence, less sensitive and hence, less suitable.

14 was B, remember emf is change in flux over time, we can see for the first bit it is increasing, so our emf graph should be positive at the beginning

 

[someth1ng]

Change in gpe is always positive.
Induced emf is in opposite direction. Lenz's law.
I think the back emf has to be smaller because there needs to be a constant supply emf for the motor to turn in a constant rotation.
For gpe the radius is not squared...

1. Wrong.
2. 14 is D.
3. No, the back emf=supply emf - They said it was IDEAL.
4. It is not GPE, it said FORCE.

 

[EinstenICEBERG]

Here is my MC answers:
1. D
2. A
3. C
4. B
5. C
6. C
7. B
8. A
9. B
10. D
11. C
12. A
13. B
14. D
15. D
16. C
17. B
18. C
19. D
20. A

Q19: I actually believe that it should be C - low electrical resistance.
Q20: To said to detect thermal radiation, this means that you use the wavelength that will allow the most radiation to be detected. Using one that is a peak means that less light is detected and hence, less sensitive and hence, less suitable.

19. I got C too.. but after thinking about it.. THE electrical resistance must be HIGH, thus it provides more thermal energy, if it were low, the eddy current would take a while to warm dat shit up. feel me?

 

[someth1ng]

14 was B, remember emf is change in flux over time, we can see for the first bit it is increasing, so our emf graph should be positive at the beginning

No, emf=-d(flux)/dt

 

[EinstenICEBERG]

I had a problem with the Transformers Question, I can't remember which question number it was. I remember that it needed to step down a voltage from 20 to 2 so you needed the fraction of 2/20 or 1/10. So therefore the Primary coil needed to be greater than the secondary coil, Which ruled out A, and D. B was 20 and 3 and C was 20 and 10. Which don't fit either.

Can someone explain where my logic took a turn.

for some reason, i think if u read it.. primary must be the output and secondary must be the input, therefore it is actually 2/20 = 1/10 , thus D: 3:30 = 1:10

 

[EinstenICEBERG]

No, emf=-d(flux)/dt

no idea what yr talking about cuz im not smart, but theres a golden rule that i use to find the answer to 14 which is D:

if the magnetic flux is 0 > EMF IS MAXIMUM and if magnetic flux is magnetic > EMF IS 0

THANKS!

 

[someth1ng]

no idea what yr talking about cuz im not smart, but theres a golden rule that i use to find the answer to 14 which is D:

if the magnetic flux is 0 > EMF IS MAXIMUM and if magnetic flux is magnetic > EMF IS 0

THANKS!

I'd understand if people make the mistake choosing B because they forget that the induced emf is NEGATIVE of the change of flux over change of time.

 

[deswa4]

Here is my MC answers:
1. D
2. A
3. C
4. B
5. C
6. C
7. B
8. A
9. B
10. D
11. C
12. A
13. B
14. D
15. D
16. C
17. B
18. C
19. D
20. A

Q19: I actually believe that it should be C - low electrical resistance.
Q20: To said to detect thermal radiation, this means that you use the wavelength that will allow the most radiation to be detected. Using one that is a peak means that less light is detected and hence, less sensitive and hence, less suitable.

I think all your answers are right, except 20 (B). 19 is indeed D because a high AC voltage means greater change in flux (more eddy currents), and high electrical resistance in the pot base means greater heat developed (as P= I^2R).

 

[brianphamm]

Here is my MC answers:
1. D
2. A
3. C
4. B
5. C
6. C
7. B
8. A
9. B
10. D
11. C
12. A
13. B
14. D
15. D
16. C
17. B
18. C
19. D
20. A

Q19: I actually believe that it should be C - low electrical resistance.
Q20: To said to detect thermal radiation, this means that you use the wavelength that will allow the most radiation to be detected. Using one that is a peak means that less light is detected and hence, less sensitive and hence, less suitable.

Where did you get thermal radiation info from? And why have low electrical resistance?

 

[brianphamm]

I think all your answers are right, except 20 (B). 19 is indeed D because a high AC voltage means greater change in flux (more eddy currents), and high electrical resistance in the pot base means greater heat developed (as P= I^2R).

+1 I Agree

 

[brianphamm]

I'd understand if people make the mistake choosing B because they forget that the induced emf is NEGATIVE of the change of flux over change of time.

I believe the negative sign accounts for Lenz's Law. I don't think it means negative EMF. It'll turn negative once the coil has rotated 180 degrees.

 

[someth1ng]

I think all your answers are right, except 20 (B). 19 is indeed D because a high AC voltage means greater change in flux (more eddy currents), and high electrical resistance in the pot base means greater heat developed (as P= I^2R).

I'm quite sure if you pick high resistance, smaller currents are also induced and hence less heat but I'm not sure. It might well be 19D.

12 is A because you need to choose one that is sensitive to all thermal radiation emitted.

 

[someth1ng]

I believe the negative sign accounts for Lenz's Law. I don't think it means negative EMF. It'll turn negative once the coil has rotated 180 degrees.

Check Wikipedia (yes, seriously) for Faraday's law of induction: it says "The induced electromotive force in any closed circuit is equal to the negative of the time rate of change of the magnetic flux through the circuit."

 

[EinstenICEBERG]

I'm quite sure if you pick high resistance, smaller currents are also induced and hence less heat but I'm not sure. It might well be 19D.

12 is A because you need to choose one that is sensitive to all thermal radiation emitted.

how do you do Q6

 

[mickstarify]

No, emf=-d(flux)/dt

Im quite sure thats back EMF, and to find EMF is simply d*flux/dt, no negative

 

[someth1ng]

how do you do Q6

Double the charge, double the flux (field lines).

 

[EinstenICEBERG]

Double the charge, double the flux (field lines).

u get da band 6 yo?