Thoughts on CSSA Physics 2008 Paper (1 Viewer)

[brendanstacey]

Somehow I calculated 80% for the power loss in the transformer. Cant you use that as its sorta like what you would look for in power loss - comparing it to the original??

 

[freelunchbrian]

remember drawing the graph?? which was the outlier?? so random... i think the 45 sec value was a bit 'out'... but definitely not wat u would call a outlier? or did i draw a graph wrong... meh

 

[proringz]

Yeah i got that 0.5998 thingo..

Anyone else think that motor was frikkin huge or did i get that wrong. i said like 278 or something for the torque.

Also that question about thought and reality was a little philosophical don't you think?

Don't you use F = BIlsintheta (force on the wire)
and then because it asked you for the torque required for this in the next question, sub into t = 2 x Fd?

The output should be equal, but it wasn't hence you had to find the powerloss.

P=IV

for primary P=12*0.05=0.6

For secondary P=6*(0.0002)=0.0012

There for, there was 0.5988 Watts of power loss.

At least, this is what I did. I'm not sure if I was right.

Yeah, got that also.

 

[pyjamapants]

Hi randoms.
I too thought the paper was quite good.

The mirror/Einstein/thought experiment question was just bizarre. I just talked about how if you couldn't see yourself then you would be able to tell that you were in an inertial frame of reference (which is impossible).

That westinghouse question was also annoyingly worded.

I got those values for the power/motor question too. phew, I really thought the motor one was wrong.

Did anyone else notice they got a lot of C's and B's for the multiple choice?? I had like 4 Cs in a row, then 3 Bs in a row. That can't be right.

Oh, and what were the answers to the stop voltage m/c question and the last m/c question (q15 about the validity of the experiment?

 

[vds700]

i thought it was allright, finished everything just in time. I realise i may have made a few silly mistakes, but overall i think ill do ok.

 

[dolbinau]

Don't you use F = BIlsintheta (force on the wire)
and then because it asked you for the torque required for this in the next question, sub into t = 2 x Fd?

I think that's right for the first one at least, but you times it by the number of turns N as well I think (if it is the force on the length of the coil)?

(q15 about the validity of the experiment?

Yeah, I put that they needed to make sure the instruments were calibrated. I reasoned that repeating=reliability, recording accurately=accuracy so checking instruments makes it 'valid'? I don't know.

 

[karnage]

From my vauge recollection of the questions:
1. Able to be applied in electricity distribution, as there is

Um... didn't it ask for another one other than electricity distribution

Hmm, was way underprepared especially for medical (didn't learn shit for it) although it was a very reasonable paper i must say.

 

[proringz]

I think that's right for the first one at least, but you times it by the number of turns N as well I think (if it is the force on the length of the coil)?

I'm not sure, but I was thinking they put the number of turns as a distraction to use t = nBIAcostheta.

 

[karnage]

Don't you use F = BIlsintheta (force on the wire)
and then because it asked you for the torque required for this in the next question, sub into t = 2 x Fd?


Yeah, got that also.

Yeaa i did that F=BILsintheta.

 

[Cob-was-here]

Oh fuck! We weren't supposed to use τ=nBIAcosθ???

 

[proringz]

Oh fuck! We weren't supposed to use τ=nBIAcosθ???

Nah, don't think so, because it was asking the torque required for the force on the wire.

 

[dolbinau]

how many marks were those questions worth? I think I've stuffed both of them.

 

[FLYHAWK14]

Hey, am I alone on this, but was anyone else like WTF with the question involving "The torque in a DC motor is always 1.5Nm"?!

 

[karnage]

Hey, am I alone on this, but was anyone else like WTF with the question involving "The torque in a DC motor is always 1.5Nm"?!

Its not always 1.5nm, coz as it turns it goes to 0 and relies on momentum to keep it turning. Also this is the part where the commutator switches the direction of the current to keep the thing spinning.

 

[gonutsmate]

Yeah didnt think it was very difficult, i think ill only lose marks on those einstein and westinghouse questions.
I finished with about an hour to go aswell.

 

[sobern]

Nah, don't think so, because it was asking the torque required for the force on the wire.

Nah the question was to do with the torque to reach this point of rotation?

i believe you cant use t = 2 x fd, as it doesnt take into account the area of the loop, which causes a difference in torque...

 

[Cob-was-here]

Hey, am I alone on this, but was anyone else like WTF with the question involving "The torque in a DC motor is always 1.5Nm"?!

The angle θ changes as the coil turns. Then when you apply τ=nBIAcosθ (or whatever equation, i cant remember), the value for torque changes as the coil rotates. I wrote something like that.... probably wrong.

 

[brendanstacey]

Haha I started off my answer by saying it was a false marketing scheme.

 

[madd-eh?]

Am I the only person in the world who hasn't done motors and generators?

 

[Daniel-08]

lol wat did u guys write 4 the westinghouse question?
i wrote about how AC generators make life easier and require less unskilled labour.
is that right?