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

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    Why is the energy stored in a capacitor half of that for a battery
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    Anybody got any predictions?
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    (Original post by AR_95)
    Why is the energy stored in a capacitor half of that for a battery
    I think it's because it's halved between the plates


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    can someone help with question 23 and 24 of june 11 section A?
    https://60abffc9b401b1c0936e01291c15...%20Physics.pdf
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    (Original post by AR_95)
    Why is the energy stored in a capacitor half of that for a battery
    Electrical energy supplied by battery per coulomb is the emf V. Therefore if a charge Q flows we have that the total energy supplied by battery is QV. On the other hand the energy stored by a capacitor is 0.5QV.
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    has anybody got any good resources for info on resonance and damping? i have a feeling we'll get some tricky questions on this to catch people out
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    Was just wondering, thought it might be a good idea if somone put together a kind of average answer table. For example spring constant usually around the 100s, capacitance usually x10^-6 etc. Would be a great help?
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    (Original post by xela238)
    Was just wondering, thought it might be a good idea if somone put together a kind of average answer table. For example spring constant usually around the 100s, capacitance usually x10^-6 etc. Would be a great help?
    I wouldn't advise this, answers and magnitudes can change dependant on different situations
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    (Original post by AR_95)
    I wouldn't advise this, answers and magnitudes can change dependant on different situations
    But would there not be rough paramteters? so if you got x10^-11 eV not J you know youve gone wrong?
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    Hey guys, can anyone explain why the answer a parabola in the vertical plane? I thought it would be in the horizontal
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    (Original post by thedon96)
    can someone help with question 23 and 24 of june 11 section A?
    https://60abffc9b401b1c0936e01291c15...%20Physics.pdf
    23 - the magnet and coil are in relative motion with each other so the coil is cutting the magnetic flux lines of the magnet therefore inducing an emf in the surrounding area which will show a reading in the ammeter as there is a current in the coil.

    (you do not need to consider lenz's law here at all so don't confuse yourself with that)

    24 -

    ε = BANωSinωt

    just apply your knowledge of maths graphs and the information they gave you to this equation.
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    (Original post by gabbons)
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    Hey guys, can anyone explain why the answer a parabola in the vertical plane? I thought it would be in the horizontal
    the circle is horizontal, so when it it falls off it will be a parabola in the vertical...

    wish i could draw it lol
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    (Original post by gabbons)
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    Hey guys, can anyone explain why the answer a parabola in the vertical plane? I thought it would be in the horizontal
    I thought this too, I think it's to do with the fact the only force acting is now weight so that must act down, in a vertical plane


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    (Original post by gabbons)
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    Hey guys, can anyone explain why the answer a parabola in the vertical plane? I thought it would be in the horizontal
    It can't be a parabola to the horizontal. Once the string breaks, the mass only has a liner velocity in the horizontal direction. There is no centripetal acceleration or force towards the centre so it goes straight forward in the x component. So the answer can't be C

    It can't be B because of the same reason above. For something to move in a circular orbit it needs a centripetal acceleration and force, which is lost when the string breaks.

    I dont think it's A because the linear velocity of the object would be tangential to the radius of the circle at the instance when it breaks

    It's D obviously. Anything you throw creates a vertical parabola
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    (Original post by Kennethm)
    23 - the magnet and coil are in relative motion with each other so the coil is cutting the magnetic flux lines of the magnet therefore inducing an emf in the surrounding area which will show a reading in the ammeter as there is a current in the coil.

    (you do not need to consider lenz's law here at all so don't confuse yourself with that)

    24 -

    ε = BANωSinωt

    just apply your knowledge of maths graphs and the information they gave you to this equation.
    23 - how come the ammeter stays constant after increasing - if it comes to rest, surely no magnetic flux lines are being cut so no emf can be induced

    24 - I did use maths knowledge so surely the 0.5B should double all Y values and the 2w should halve all x values?
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    (Original post by becca9621)
    Anybody got any predictions?
    I predict I'll be needing a lot of lube for the exam tomorrow
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    Hey, can anyone answer this question for me? I can do it just by thinking about it, but what equations could you use for this? Thanks!

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    (Original post by thedon96)
    23 - how come the ammeter stays constant after increasing - if it comes to rest, surely no magnetic flux lines are being cut so no emf can be induced

    24 - I did use maths knowledge so surely the 0.5B should double all Y values and the 2w should halve all x values?
    23 - they didnt say the reading was constant, answer B says that the magnetic flux linkage stays constant.

    24 -

    ε = BANωSinωt

    B is 0.5 and ω is doubled so the first part cancels meaning the answers is out of A and B.

    Sinωt is left so its Sin2ωt therefore halving the X directions ^^
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    (Original post by bwr19)
    Hey, can anyone answer this question for me? I can do it just by thinking about it, but what equations could you use for this? Thanks!

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    I got the answer D, if thats correct Ill explain to you
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    Really think the six marks will be on SHM/DAMPING/RESONANCE

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