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

[syper]

I thought that 10 was D. It's a transformer so AC is used. It varies sinesoidally.

The primary coil is powered by a battery, which is a DC not an AC power source.

Answer to question 10 is A.

It said "to investigate the operation of a transformer", investigations don't always work

 

[SureBluff]

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

Didn't read the thread, but I think these answers are correct because I went over it with some friends.

 

[lonely_devil]

1. C
2. B
3. D
4. B
5. D
6. A
7. C (but the answer is D... stupid trick question...)
8. B
9. A (this is wrong too...)
10. D (got it wrong again...)
11. A
12. C
13. D
14. C
15. B (sigh... 25% chance... n i guessed it wrong...)

 

[SureBluff]

dammit, still made a mistake in that one ^^^

sigh

I got 4 multiple choices wrong so far.

 

[drewgcn]

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

Didn't read the thread, but I think these answers are correct because I went over it with some friends.

Hey lawrence

12 is C. The velocity parallel to the field direction is unaffected.

I think 9 is B but I'm not sure. It doesn't make sense that it would be an alternating current because there is no coil. I.e. the eddy currents should always be in the same direction.

I think I got them all but fooled myself on 7. Damn those bastards for that subtle trick

 

[gamecw]

also i disagree with #7 .. i think it 's c. lol

lol u got TRICKED, did u just subsitute the values in the equation F=IBlsin@?

well if u look carefully, the magnetic field is still perpendicular to the coil

l=0.4/sin45
F=BlI=0.5x3x0.4/sin45=0.849N (@ is still 90)

and 15 u use frequencyxwavelength=speed of light

find the frequency when the ligh has 187nm then plug the values n u will find it to be Al

 

[SureBluff]

who the heck are you guys?

I bet one of you is Lilster

I got 5 multiple choices wrong

FIVE!!!!

that's shocking man.

 

[shinji]

think I got them all but fooled myself on 7. Damn those bastards for that subtle trick

i concur! lol
seems like they threw some curve balls at us this year. still, i think i performed better than i did in the trials .. hopefully~!

 

[dartm2]

For Q8 I think is b)

the way i see it, try using either the right hand puch rule or left hand whatever you want to try and determine what way the current would be induced....... it dosn't work. Now imagine the coil has rotated around so that all you see is the one line...... you get a direction of the induced current.

So when the coil is at the position in the diagram no current is being generated, and is therfore b)



THe second way to look at it is if you imaging the coil rotating, the wire XY is moving towards you, parrellel with the flux lines, Meaning no current is induced.

Conclusion i think that its b.....


Q10 I think is a

Why? The question say that the student turns the on and then off, thats it. Current flows for a while then stops. Just from this you can eliminate D and B (as voltage continues with current so you cant have 2 spikes in the primary coil) leaving A and C, but a current is only induced when flux cutting occurs (when the swtched is first closed then re opened) so you would get 2 spikes in the secondary coil ..... which is a.


Tell me what you think, though i think these are right

 

[shinji]

lol u got TRICKED, did u just subsitute the values in the equation F=IBlsin@?

well if u look carefully, the magnetic field is still perpendicular to the coil

l=0.4/sin45
F=BlI=0.5x3x0.4/sin45=0.849N (@ is still 90)

and 15 u use frequencyxwavelength=speed of light

find the frequency when the ligh has 187nm then plug the values n u will find it to be Al

lol. damn u~!

read above post~! lol

<3 ur avatar though. hehe

 

[suchet_i]

is the answer to 9 c?? i m pretty sure it is .. if it is i got 100% in multiple choice

 

[syper]

is the answer to 9 c?? i m pretty sure it is .. if it is i got 100% in multiple choice

Nah pretty sure it's B

 

[Bricnic]

"Let's Undermine each other's confidence" should be the alternate title for this thread -_-
1. C
2. B
3. D
4. B
5. D
6. A
7. C* (Yeah I got tricked too. Damn those examiners.)
8. A (I'll stick with the flux, as opposed to E.M.F argument here)
9. A? (Wasn't sure, but this didn't appear to be a proper generator to me. Why would the induced current bother flowing through the globe, which has such high resistance, when it is much easier for it to flow through the conductors which are not separated, i.e. travel through the handle or metal disc exclusively?)
10. A
11. A
12. C
13. D
14. C
15. B* (After reading this forum I'm not so sure anymore, in the exam I didn't think any of those metals quite matched up with c=wavelength*frequency, but Be seemed the closest.)
Probably looking at 12/15. I'm happy with that

 

[suchet_i]

mate if u look at eddy currents forming from the point of view of the handle, they will be forming in an anticlockwise direction. such a direction of the current will mean that it travels through to x to the globe and to y and so on .. if you understand what i am saying how can i be wrong?

 

[Bricnic]

mate if u look at eddy currents forming from the point of view of the handle, they will be forming in an anticlockwise direction. such a direction of the current will mean that it travels through to x to the globe and to y and so on .. if you understand what i am saying how can i be wrong?

...I assume you mean you're looking at the diagram from the side where the south pole of the magnet will be closest to you. Wouldn't the eddy currents be formed in a clockwise direction, to oppose the anti-clockwise motion of the handle which created them?

 

[suchet_i]

no you wouldnt because when formed antil clockwise they will form magnetic poles (such a near the N of the magnet there witll be a S and near the S of the magnet the eddy currents will create a N) thus these opposite poles will cause attraction so its anticlockwise

 

[robmeister]

yeha anyone know for certain answer for 9? i was tossing up between A and D went wit hD as i thought A would be really sneaky and would make me angry.

 

[suchet_i]

i m 99.95% sure its C

 

[zeek]

If you apply the right hand palm rule to question 9:

Palm in direction of motion of the disc (palm facing away from you)
Fingers going from left to right (joint to tips)
.: Your thumb faces up and the conventional current flows through X first and then through to Y... so i guess it's C*

 

[typical_azn]

the most controversial 3 quetions, 8, 9 and 10.

for 8 im agree with everyone who got A coz it is, well proof is, it asks variation in magnetic flux, flux is calculated by theta=BxAcosY, confusion is, its Y is the angle between the perpendicular of the flux and area, if u know what i mean, where B is magnetic field strength and A is area or coil, therefore greatest when the area is perpendicular to the magnetic field

question 9 is B its to long to explain, but u can go to this link and check it out for urself. oh yeah, about it not have a split ring commutator, doesnt make it AC, it all depends on rate of change of magnetic flux through the coil or in this case disc.
http://www.zamandayolculuk.com/cetinbal/faradaydisk.htm kindly provided by RingerINC

question 10 has many uncertainties, im not to sure either, it doesnt say wether its AC or DC, and another thing im not sure about, but can help in the investigation of the real answer is wether the induced current in the second coil flows in the same direction as that of the original one, or does it flow in the opposite direction??