Want to compare multiple-choice answers? (1 Viewer)

[myeewyee]

It should be b.

 

[XcarvengerX]

Good then.
This is the most correct answer according to the majority of BoSers. Take this as official until the Board of Studies releases the actual answers. So if you want to mark yours, use this:
1. C
2. B
3. D
4. B
5. D
6. A
7. D
8. A
9. B
10. A
11. A
12. C
13. D
14. C
15. A

 

[StYlez-]

someone explain to me why 10 is A again, i still dont get it.

 

[Desiree]

1. C
2. C
3. D
4. B
5. C (i couldn't decide between C and D, enny menny minny moe)
6. A
7. B
8. B
9. C
10. B
11. A
12. C
13. D
14. C
15. B (enny menny)

 

[Lachdog]

Yeh i don't understand how 10 could be a either?

Transformers run with AC.

My answers were: 1 c 2 b 3 d 4 b 5 d 6 a 7 d 8 a 9 d 10 d 11 a 12 c 13 d 14 c 15 a.

 

[Lockhart]

Altough I put 10 d as well, its wrong. 10 is a as while the transformer is turned on there is back emf in the wire which means the voltage will gradually rise to a maximun. This constitutes a changing magnet flux which will cause voltage in the secondary coil when it is being turned on and off.
The cell, is a battery therfore it must be DC. Which means while its running it will have a constant voltage.

 

[Lockhart]

Again while I put B for question 8 it is actually A.
magnetic flux is defined by (B{perpendicular to}A) therefore when the coil is initially at right angles magnetic flux is a maximun. When it is parrelle, no area is being threaded through the field so A becomes zero and flux is zero at 90 degrees.

 

[Lockhart]

the only question that is in doubt is question 9.
I personally put A.
This appartatus is the same that functions in a electromagnetic break, it produces eddy currents within the wheel.
What I fail to see is why these currents should travel trough a loaded wire at all, where there is greater resistance. shouldn't they remain within the wheel travelling in two circles completeing the circiut and releasing heat by doing so.
What reason is there to sugest that the current will move through the wire.
That was my reasoning, however some people came up with an interent site suggesting that this does produce a current. In which case I don't doubt that i'm wrong. But if anyone could explain the flaw in my reasoning i would be grateful.

 

[Lockhart]

just for anyone whiose interested heres a rough sample of how most of us seem to have gone in the exam.

1. C C C C C C C A C C C
2. B B B B B B B B B B B
3. D D D D C D D D D D D
4. B B B B A B B B B B B
5. D D D D B D D D B D D
6. A A A A A A A A A A A
7. D D D C B D C B B C D
8. B C B A B A A A B A A
9. A A B B D D B B B D C
10. D A D B B D A A B D A
11. A A A A A A A A A A A
12. C C C C C C C C C C C
13. D D D D D D D D D D D
14. C C A C C C C C D C C
15. B A A A A A D A D A A

1. C C C C C C C C C B C
2. B B D B B B B B B A B
3. D D D D D D D D D C D
4. B B B B B C B B D C B
5. D D D D D D C D A B D
6. A C A A A A A A A B A
7. D C D D C C C C C D D
8. B B B A A B A A A B A
9. B D B D A A B B B A B
10. A D A A A D A D D C A
11. A A A A A A A A A B A
12. C C C D C D C C C A C
13. D C D D D D D D B D D
14. C C C C C C C C B A C
15. A B A A B A A A A C A

Green are correct answers with perhaps question 9 being different

Red are when students got a wrong answer

So there were out of the first 21 students to reply:

5 fourteens
6 thirteens
2 twelves
1 eleven
2 tens
3 nines
1 two

 

[shinji]

lol, i got either 12-13/15 for mc
13 if 9 is b ^_^

 

[XcarvengerX]

Nice Lockhart. Thanks for tabulating them. Note that there are some incorrect answers that you didn't make it red. (question 7 and 13).

Questions 7, 8, 9 and 10 pose to be the most problematic ones.
So no one got full mark?

 

[meekzy89]

1. c
2. b
3. d
4. b
5. b [i kno this is wrong]
6. a
7. c
8. b
9. c [my hand rule didnt work.. or something]
10. a [i think its wrong]
11. a
12. c
13. d
14. c
15. a

umm i think i got 11/15... dammit!!

 

[fizzwizz]

Hi The correct answer to this q is B I think.Use Lenz's law to answer it, and we will take answer C to show that it is incorrect.

If current goes through globe from X to Y then a current moves upwards from brush Y to the handle. Now think of this current as a current in a single conductor pointing upwards, passing through the magnetic field which is directed from left to right. Now use the right hand push rule: current up, fingers pointing left to right................this produces a force on the conductor (disc) into the page. But it is already moving into the page (at the bootom) so this force would increase its jmotion, not decrease its motion as required by lenzs law. A force has got to act on the conductor pushing it out of the field, as it enters the field. Using current flow downwards from handle to brush Y gives you this force. So answer is B.

 

[switchfootfan]

yeah thinking around 11-13 for mc]
1c
2b
3d *i think i put that*
4b
5a (i know i screwed up- dont know how i got that....)
6a (its either a or b and i dont think it attracts)
7b (i think its c, your right)
8a (its flux)
9borc (cant remember- think it might have been b that i put- hope so)
10c (this is open to debate- i pritty sure you can get dc transformers)
11a (obviously)
12c
13d
14c (E=v/d and perpecx does not conduct electricity)
15a (v=wavelegthx frequency)
thats what i got

 

[meekzy89]

Hi The correct answer to this q is B I think.Use Lenz's law to answer it, and we will take answer C to show that it is incorrect.

If current goes through globe from X to Y then a current moves upwards from brush Y to the handle. Now think of this current as a current in a single conductor pointing upwards, passing through the magnetic field which is directed from left to right. Now use the right hand push rule: current up, fingers pointing left to right................this produces a force on the conductor (disc) into the page. But it is already moving into the page (at the bootom) so this force would increase its jmotion, not decrease its motion as required by lenzs law. A force has got to act on the conductor pushing it out of the field, as it enters the field. Using current flow downwards from handle to brush Y gives you this force. So answer is B.

HAHAHAHAHAHAHA!!! OMG i know what ive done! .. i used my left hand.. cuz i was friken WRITING with my right
LOL!!!!!

omggg can i get any more stupider! BAHAHA!!!
thankuu

 

[XcarvengerX]

7 is D because you have to use pythagoras to calculate the diagonal length AND also sin 90 NOT sin 45. If you use either pythagoras but sin 45 OR sin 90 but not pythagoras, then you get C which is incorrect.

 

[eX-Bhai]

7 is D because you have to use pythagoras to calculate the diagonal length AND also sin 90 NOT sin 45. If you use either pythagoras but sin 45 OR sin 90 but not pythagoras, then you get C which is incorrect.

that is incorrect. The answer is C

By using basic trig, Sin 45 = 0.4 / L
Therefore 0.4 = L.sin45

By using the formula F = BILsin@

B = 0.5 T
A = 3 A
Lsin@ = 0.4

Therefore F = 0.6 N

 

[XcarvengerX]

that is incorrect. The answer is C

By using basic trig, Sin 45 = 0.4 / L
Therefore 0.4 = L.sin45

By using the formula F = BILsin@

B = 0.5 T
A = 3 A
Lsin@ = 0.4

Therefore F = 0.6 N

The bold line is the part where you got it wrong. Look at the diagram again. The conductor is already perpendicular to the magnetic field line, therefore you use sin 90. The 45 degree is to indicate that the conductor is indeed passing through as the diagonal of the square magnetic field.

 

[fizzwizz]

D is correct. Angle theta is misunderstood - it is the angle between the plane of the current (the page) and the plane of the magnetic filed (many parallel planes coming in or out of page) In this case that angle is 90 degrees. Use pythag (square root of (0.5 squared + 0.5 squared) to find L. Then use F=BIL (SIN 90) to give D

 

[gamecw]

i got 9&10 wrong... so 13/15