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

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    But if you use it for a point charge, how to u know which charge to use because they didnt specify whether they were asking it E for 30nc or 60nc..... I personally found the whole electric potential calculations so misleading/unclear..
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    (Original post by Vincent Song)
    The work done should be positive I think.
    Thats true. The work done is positive. Since the potential is negative it means that the charge causing the potential is negative. Therefore for a positive charge to be moved from a less distance to a further distance from the negative charge, work "has to" be done on the positive charge because they are attracted. Though i was not conscious of this reasoning during the exam


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    (Original post by dmp1188)
    But if you use it for a point charge, how to u know which charge to use because they didnt specify whether they were asking it E for 30nc or 60nc..... I personally found the whole electric potential calculations so misleading/unclear..
    You have to use the charge causing the potential, that is 30nc


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    (Original post by sam_97)
    The work done should be positive because it was the work done on a positive (60nC) charge
    Not necessarily. If the positive charge was moved from a greater distance to a closer distance to the negative charge then the work done would be negative


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    (Original post by Vincent Song)
    .
    I got that value in 2c(i). Which formula? Is it E=Q/(4pie sth r^2)?
    Yeah, i think


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    (Original post by Mehrdad jafari)
    Not necessarily. If the positive charge was moved from a greater distance to a closer distance to the negative charge then the work done would be negative


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    Oh yeah good point!
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    (Original post by Dalek1099)
    Why is damping reduced the metal ring does increase the surface area as yes the front of the ring covers up the surface area of the cone under it(so no increase there) but those who say that the surface area hasn't increased aren't accounting for the increase in surface area between the ring and the cone, draw it in 3D and you will see what I mean.
    The ring adds mass, therefore the pendulum with the added ring has a larger momentum for a given speed which is governed only by the displacement of the bob which we assume to be the same. The damping force is provided by air resistance which is proportional to v^2 and hence the bob with the ring on has a larger mass and thus for constant damping force it is slowed down less as the impulse is the same in both cases.
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    (Original post by Protoxylic)
    The ring adds mass, therefore the pendulum with the added ring has a larger momentum for a given speed which is governed only by the displacement of the bob which we assume to be the same. The damping force is provided by air resistance which is proportional to v^2 and hence the bob with the ring on has a larger mass and thus for constant damping force it is slowed down less as the impulse is the same in both cases.
    Surface area increases though and damping is proportional to surface area also.I think I have screwed up so much on the written questions(except the 6 marker bizarrely) losing at least half of question 1 and 5 marks for the electromagnetic induction at least I think I have got 24/25 for multiple choice.
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    (Original post by Dalek1099)
    Surface area increases though and damping is proportional to surface area also.I think I have screwed up so much on the written questions(except the 6 marker bizarrely) losing at least half of question 1 and 5 marks for the electromagnetic induction at least I think I have got 24/25 for multiple choice.
    Yes, but the bob is going so slow that the increased surface area has negligible effect in comparison to the increased weight/momentum
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    (Original post by Dalek1099)
    Surface area increases though and damping is proportional to surface area also.I think I have screwed up so much on the written questions(except the 6 marker bizarrely) losing at least half of question 1 and 5 marks for the electromagnetic induction at least I think I have got 24/25 for multiple choice.
    yea but then i feel like most people didn't do quite well on written answers, and given that there was a wrong question in the paper, boundaries should be lower than usual I think, cos AQA would definitely have to compensate for their mistake
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    (Original post by Dalek1099)
    Surface area increases though and damping is proportional to surface area also.I think I have screwed up so much on the written questions(except the 6 marker bizarrely) losing at least half of question 1 and 5 marks for the electromagnetic induction at least I think I have got 24/25 for multiple choice.
    What mark did you drop on the MC?


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    I forgot the - on the electrical field strength, will they condone this?
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    (Original post by DomRauba)
    I forgot the - on the electrical field strength, will they condone this?
    Me too. I hope so. Similar calculations in the past have had a negative sign in brackets suggesting they accept both answers equally.


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    (Original post by CD223)
    Me too. I hope so. Similar calculations in the past have had a negative sign in brackets suggesting they accept both answers equally.


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    cheers pal
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    When AQA come to mark my answer to the damping question:

    https://twitter.com/examproblems/sta...92867686109184


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    Did anybody take screenshots of that multi choice section? Won't come up on the link, shows section B.

    What's the general consensus on this paper? Generally was seen as a fairly nice multi choice but a tougher written section at my school. People weren't too happy with how it went tbh
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    (Original post by JJBinn)
    Did anybody take screenshots of that multi choice section? Won't come up on the link, shows section B.

    What's the general consensus on this paper? Generally was seen as a fairly nice multi choice but a tougher written section at my school. People weren't too happy with how it went tbh
    Yeah MC was seen as nice and written quite tough at my college. Hoping boundaries are around 60 for an A* given AQA's **** up.


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    Section B question 5, calculatio part, does the question mention the string is horizontal?
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    (Original post by CD223)
    When AQA come to mark my answer to the damping question:

    https://twitter.com/examproblems/sta...92867686109184


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    Whoever marks my paper will react in exactly the same way when they see my answer to that question hahaha
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    (Original post by CD223)
    When AQA come to mark my answer to the damping question:

    https://twitter.com/examproblems/sta...92867686109184


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    Haha, that actually made me laugh


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