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# AQA Physics PHYA4 - Thursday 11th June 2015 [Exam Discussion Thread] watch

1. (Original post by Chazley123)
or 0.06/0.5 = 0.12 v ?? as emf= BAN(linkage)/t - faradays law??
I did the same as you chazley
2. (Original post by Protoxylic)
I can't remember, but if that is true then the rotation of the coil would vary. Either way if it did say increased uniformly then the emf would be constant meaning there would be no need to ask for the mean emf.
It just said the coil was rotated 90 degrees.
3. What a fail. You can see in the link its clearly not a mark scheme..
4. (Original post by SuperMushroom)
What a fail. You can see in the link its clearly not a mark scheme..
Lol bants
5. (Original post by Chazley123)
change in momentum equal to impulse (Ns)

rate of change of momentum - I/t (Ns/s) = (N) - equivalent to weight =mg
Are you agreeing with me that its D? (rate of change in momentum)
6. (Original post by Protoxylic)
I can't remember, but if that is true then the rotation of the coil would vary. Either way if it did say increased uniformly then the emf would be constant meaning there would be no need to ask for the mean emf.

How many marks do you think you lost overall?
7. I don't think that solution from AQA on the graph question is fair at all, I just completely skipped it because I knew it must have been a misprint!

Not that it will make much of a difference though, honestly think I've only got about 30/75 on the entire paper at this point
8. (Original post by NEWT0N)

How many marks do you think you lost overall?
Just the 0.12V mean emf is under debate atm. The rest of the paper went well.
9. (Original post by StarvingAutist)
It just said the coil was rotated 90 degrees.
By the way, can you recheck your maths. e=dN(phi)/dt so e dt = dN(phi)

So sum of all e, S(e), shouldn't equal Awsin(wt) dt, surely?

The sum of the emfs would just be a sum, not an integral since if you integrate emf forward in time you get et not S(e). Either that or I'm not following your maths correctly
10. (Original post by Protoxylic)
Just the 0.12V mean emf is under debate atm. The rest of the paper went well.
How did you get 0.12? Im pretty sure the answer was 0.08v ??
11. (Original post by SuperMushroom)
How did you get 0.12? Im pretty sure the answer was 0.08v ??
I did get 0.08V. I'm labeling it as the 0.12V Q lmao
12. Has anyone posted the questions/ distribution of marks? Trying to figure out if I still have a future without getting full UMS on unit 5 lol
13. (Original post by Protoxylic)
I did get 0.08V. I'm labeling it as the 0.12V Q lmao
Oh ok my bad haha, just happy someone else got 0.08v aswell
14. (Original post by NEWT0N)

How many marks do you think you lost overall?
Bet you were laughing when the 6 marks was on your laws Newton?
15. (Original post by Protoxylic)
By the way, can you recheck your maths. e=dN(phi)/dt so e dt = dN(phi)

So sum of all e, S(e), shouldn't equal Awsin(wt) dt, surely?

The sum of the emfs would just be a sum, not an integral since if you integrate emf forward in time you get et not S(e). Either that or I'm not following your maths correctly
e = -N dphi(t)/dt
therefore Sa,b(e)dt = [Nphi(t)]a,b
No negative because of sin and cos blah blah blah

It should definitely be an integral; time is continuous.
16. For the how to find initial charge question, I thought of it this way

V = IR applies with the initial current being equal to V/R

Also the charge stored, Q = CV which rearranges to V = Q/C

Equating the two you get Q/C = IR, so Q = CIR

I know the area under the graph makes much more sense, but would I get any marks for this??

The Fuhrer reacts
18. Please, someone reassure me that I'm not the only one who thinks that was awful? I'm really angry and upset It was just full of so many ****ty questions. I need some reassurance.
19. (Original post by Protoxylic)
So you tell me why dividing a number you got given, by another value you got given constitutes 2 marks. Contrast this to the previous question where you were asked to multiply 3 numbers together for 1 mark (flux linkage) then asked the units for another mark (wbturns). All the physicists (as in the teachers) in my school agree with the use of the rms value
Probably one mark for working, two for answer with no working and there was a mark for the unit.
20. (Original post by EHR223)
Bet you were laughing when the 6 marks was on your laws Newton?
lol yes, huygens got that one wrong I talked to him after the exam

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