# AQA PHYA4 ~ 13th June 2013 ~ A2 PhysicsWatch

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6 years ago
#1061
(Original post by MisterE1)
Can anyone else confirm that the y axis was change in flux linkage?

and i'm going to school tomorrow, i'll ask my teacher if they have a copy of the paper :P
it was asking us to draw a graph of emf, so yeah...

emf is rate of change of flux linkage
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6 years ago
#1062
(Original post by Jack93o)
that diagram is showing a positive cosine graph for flux

and apparently the flux graph in that exam was negative
Huh... you're not making sense.

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6 years ago
#1063
(Original post by cooldudeman)
Huh... you're not making sense.

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in the exam, there were two graphs

one was showing how flux changes over time, and this graph was minus cosine (unless someone remembers it was something else?)

and the second graph below was the one which we had to use to draw how emf varies

the CGP flux graph posted robmarkey shows a positive cosine graph, and it shows a positive sine graph for emf

so what I was saying is that the graphs in the CGP book is not exactly the same as in our exam
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6 years ago
#1064
(Original post by marcolliwright)
IT definitely did not say change in flux linkage, if it did the gradient of the line would not represent the emf, but the change in change of flux linkage. No one plots a graph of change in flux linkage against time lol

EDIT: actually that is the same as emf against time but that's the graph they asked you to draw so they definitely wouldn't print it in the paper in the first place
from what i can remember the y-axis was change in flux linkage
emf is the rate of change of flux linkage
so the gradient gave the emf
i dont know i might be wrong but thats what i can remember we'll see when someone gets hold of the paper
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6 years ago
#1065
(Original post by Dirtybit)
Lmao I actually thoughht that when i turned the page it would be a 6 marker All in all not bad paper could have been harder. wbu?
Haha. Yeah it definitely could have been harder. Though that didn't stop me from making some of the most trivial errors known to man. I finished 15mins early...and from seeing some of the (very debatable) answers on here it looks like i might not get my A on this paper.

Anyway. Just trying to focus on unit 5 now, but the astrophysics option just makes me sleepy!
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6 years ago
#1066
(Original post by smatts)
Hi guys, just had one question about the exam which has been puzzling me. I may have incorrectly read the question, but correct me if I'm wrong:
In the question regarding the parallel discs where it asked the time between consecutive sparks if the capacitance were to be increased. I understand the logic behind thinking that if capacitance goes up, then the time constant goes up, therefore the time between sparks increases. However i specifically remember the question telling us that the current (rate of flow of charge) was constant, hence the system would not be an exponential increase of charge but rather a constant increase in charge. Therefore for a greater capacitance, a smaller charge must be stored to achieve the required 30'000V, therefore the time between sparks would in fact be shorter. Please explain to me if my reasoning is correct?
I specifically remember asking myself whether this was a trick question and gave it an extra thought.
A larger capacitance means a larger charge stored, Q=CV
Increase C, increase Q, not a decrease!

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6 years ago
#1067
Also why is the magnetic field on page 114 (nelson thornes, AQA) directed into the cyclotron?
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6 years ago
#1068
Guys and girls...since we're still debating the +/- sine curve....can we also debate that multiple choice ratio question where most people got 2/3 but people are saying the answer is 1/3? Is it concrete that the answer is 1/3?

I'm just clutching on to straws here really.. Should have f'ing started revising earlier.
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6 years ago
#1069
(Original post by Jack93o)
in the exam, there were two graphs

one was showing how flux changes over time, and this graph was minus cosine (unless someone remembers it was something else?)

and the second graph below was the one which we had to use to draw how emf varies

the CGP flux graph posted robmarkey shows a positive cosine graph, and it shows a positive sine graph for emf

so what I was saying is that the graphs in the CGP book is not exactly the same as in our exam
Yh so the answer to ours is -sin. I thought you were saying it isn't

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6 years ago
#1070
(Original post by saba146)
from what i can remember the y-axis was change in flux linkage
emf is the rate of change of flux linkage
so the gradient gave the emf
i dont know i might be wrong but thats what i can remember we'll see when someone gets hold of the paper
I think we are just getting our wording confused... the y axis didn't literally say "change in flux linkage" however that graph represented how the flux linkage is changing over time.

If the y axis did actually say change in flux linkage (which it didn't) then it would be the same as the emf-time graph. What the y-axis itself represented was the flux linkage. It was the whole graph which showed the change in flux linkage.
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6 years ago
#1071
(Original post by cooldudeman)
Yh so the answer to ours is -sin. I thought you were saying it isn't

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yeah thats what I was implying

at the start I thought it was positive, but it now seems like it should've been negative
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6 years ago
#1072
(Original post by kingm)
Guys and girls...since we're still debating the +/- sine curve....can we also debate that multiple choice ratio question where most people got 2/3 but people are saying the answer is 1/3? Is it concrete that the answer is 1/3?

I'm just clutching on to straws here really.. Should have f'ing started revising earlier.
as with all questions where we can't decide what the answer is, we'll have to wait till someone gets hold of the paper! I personally got 2/3!
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6 years ago
#1073
im hopingg.. the grade boundaries are similar to the took in jan... man.. physics is just too hard
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6 years ago
#1074
(Original post by xoxoxoxoxox)
im hopingg.. the grade boundaries are similar to the took in jan... man.. physics is just too hard
The grade boundaries in Jan 13 were the highest ever
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6 years ago
#1075
The graph was negative....yea I did say change In flux I've got the paper here.
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6 years ago
#1076
(Original post by Robmarkey)
The graph was negative....yea I did say change In flux I've got the paper here.
If you've got the paper then upload it. Not like anyone's been asking for it you know..
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6 years ago
#1077
(Original post by Robmarkey)
The graph was negative....yea I did say change In flux I've got the paper here.

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6 years ago
#1078
(Original post by MSI_10)
If you've got the paper then upload it. Not like anyone's been asking for it you know..
I'm filling in the answers but I got to check them so there not uploaded with silly mistakes, it will be up first thing tomorrow section B anyway.but I can assure you that the graph is negative!
2
6 years ago
#1079
(Original post by Robmarkey)
I'm filling in the answers but I got to check them so there not uploaded with silly mistakes, it will be up first thing tomorrow section B anyway.but I can assure you that the graph is negative!
Try doing the max emf one. What answer do u get? The max gradient method
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6 years ago
#1080
(Original post by Robmarkey)
I'm filling in the answers but I got to check them so there not uploaded with silly mistakes, it will be up first thing tomorrow section B anyway.but I can assure you that the graph is negative!
I wouldn't mind a blank copy! I just want to know the questions! :P

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