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

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Do you think Ill get the mark for flux linkage unit if I just put 'Wturns'?


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Original post by k9000
The question asked what was incorrect.. B was incorrect so that was the correct answer (confusing ik)


ffs, that's annoying
Original post by imyimy
does anyone remember a brief summary of each question? e.g. like question 1 was resonance then damping.


Question one asked you to describe what "forced oscillations" and "resonance" mean with regard to amplitude, frequency and phase difference.

There was a definition of Coulomb's Law
I wrote Wb Turns too!

Original post by louisg565
Do you think Ill get the mark for flux linkage unit if I just put 'Wturns'?


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Aw I thought it was Wb
Ok this was probably the easiest paper to of come up

having said that its the paper I ****ed up in the most


good bye firm choice
Reply 4246
Avatar for k9000
k9000
2
Newton's first law at the end i put because no force in direction of velocity (always tangential) it remains at constant speed. Is that ok for the first law
Guys, let me know if you got the same answers

ImageUploadedByStudent Room1434022386.412958.jpg



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Original post by TheRAG
what did y'all put for the six marker?


My answer:

There is always a centripetal force acting towards the centre greater than zero so the mass always accelerates towards the centre.
There is a gravitational force acting on the mass (mg). This means the string has to subtend an angle theta < 90 degrees in order to ensure there's a vertical component of centripetal force in order to oppose the weight of the mass. This means the string in practice is never horizontal. Centripetal force always acts at right angles to the motion so F=0 in the direction of motion this means there is no acceleration in the direction of motion and hence the speed of the mass remains constant throughout revolutions
Original post by NEWT0N
I read what you said and I disagree: for damping to occur it is only necessary for the amplitude must be affected. Damping forces reduce amplitude, not time period.


Oh dear then
Original post by AR_95
Ok this was probably the easiest paper to of come up

having said that its the paper I ****ed up in the most


good bye firm choice


Welcome 2 the club :badger:
Reply 4251
Avatar for crs96
crs96
For flux linkage i put Tm(squared) ? is that ok?

Also what did people put for the distance between the surfaces of the 2 spheres mass M radius R when F/9?

2R, 4R, 8R or 12R?
Original post by crs96
For flux linkage i put Tm(squared) ? is that ok?

Also what did people put for the distance between the surfaces of the 2 spheres mass M radius R when F/9?

2R, 4R, 8R or 12R?


I said 2R ??
Original post by NEWT0N
It's just lenz's law. A flux moving in the opposite direction causes the coil to set up a field in the opposite direction to the flux. Initially it sets up a field opposite to a flux moving in direction X (say), then it sets up a field in the opposite direction to -X. X is opposite to -X so the induced current the second time round is opposite.

The only thing that changed was an increase in resistance. They didn't reverse the direction of the current. So why would a field be produced in the opposite direction?
Original post by NEWT0N
What did people put for the forced vibrations?

I remember using the cgp explanation: A system can be forced to vibrate by an external periodic force called the driving force. If the driving force does not have the same natural frequency as the system, the amplitude of oscillation will be smaller than that in free vibration.


Yeah I said that but quoted phase differences
Original post by Mehrdad jafari
Guys, let me know if you got the same answers

ImageUploadedByStudent Room1434022386.412958.jpg



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I think your acc graph is wrong (not sure). The distance between planets is definitely 4R as initially F is proportional to 1/4R^2 then it becomes 1/9 F so 4*9=36 root36=6 then 6-2=4 (as it says between planets so u remove each radi)
Original post by louisg565
Do you think Ill get the mark for flux linkage unit if I just put 'Wturns'?


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Hope so but probably not..
I did the exact same ffs.
Original post by crs96
For flux linkage i put Tm(squared) ? is that ok?

Also what did people put for the distance between the surfaces of the 2 spheres mass M radius R when F/9?

2R, 4R, 8R or 12R?


4R

Original post by SuperMushroom
Welcome 2 the club :badger:


Surely that is the funniest Emoji?
I don't think i have done as well as i had hoped. What do you guys think the grade boundaries will be?
Original post by chizz1889
I think your acc graph is wrong (not sure). The distance between planets is definitely 4R as initially F is proportional to 1/4R^2 then it becomes 1/9 F so 4*9=36 root36=6 then 6-2=4 (as it says between planets so u remove each radi)


His graph is correct

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