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

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    any explanation for question 19
    http://filestore.aqa.org.uk/subjects...W-QP-JUN10.PDF
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    (Original post by Corectspelling)
    any explanation for question 19
    http://filestore.aqa.org.uk/subjects...W-QP-JUN10.PDF
    F = BIL

    If the current is reversed in its direction, due to Fleming's LHR, the force will also reverse direction.

    If the current is doubled in its magnitude, due to F = BIL, the force will also double in its magnitude.

    The scale reads a force exerted on it by the magnet and wire combination. If F doubles and reverses its direction, then because the wire is fixed, an initial reading of 112g will now read -224g (= -2 x 112g).

    Does that help?


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    (Original post by CD223)
    F = BIL

    If the current is reversed in its direction, due to Fleming's LHR, the force will also reverse direction.

    If the current is doubled in its magnitude, due to F = BIL, the force will also double in its magnitude.

    The scale reads a force exerted on it by the magnet and wire combination. If F doubles and reverses its direction, then because the wire is fixed, an initial reading of 112g will now read -224g (= -2 x 112g).

    Does that help?


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    Why is it negative?
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    Do we need to know about the right hand rule? or is it just the left hand one
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    (Original post by gcsestuff)
    Do we need to know about the right hand rule? or is it just the left hand one
    You only need left hand rule and Lenz's law.
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    (Original post by Corectspelling)
    Why is it negative?
    Because the scale was zeroed after the magnet was placed on the scale. So when you take the magnet of the scale then the scale will read negative of the mass of the magnet


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    (Original post by Corectspelling)
    Why is it negative?
    The scale was zeroed before any of the changes took place. If I'm honest it is a very badly worded question. If anyone else can shed light on this then I'd appreciate it.


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    (Original post by CD223)
    The scale was zeroed before any of the changes took place. If I'm honest it is a very badly worded question. If anyone else can shed light on this then I'd appreciate it.


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    That's true. In fact most of the questions they ask are badly worded and lack details


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    (Original post by Mehrdad jafari)
    Because the scale was zeroed after the magnet was placed on the scale. So when you take the magnet of the scale then the scale will read negative of the mass of the magnet


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    ahhhh i see, thanks m8 quite a tricky question
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    (Original post by Corectspelling)
    ahhhh i see, thanks m8 quite a tricky question
    No problem!
    Yeah, they are quite tricky. In the exam don't judge a question too quickly. Read the question carefully before you answer it.


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    (Original post by Mehrdad jafari)
    No problem!
    Yeah, they are quite tricky. In the exam don't judge a question too quickly. Read the question carefully before you answer it.


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    I'd have got it wrong in the exam. I initially thought -112g as the actual change in weight is -224g, and I saw it was initially 112g, so I did 112 - 224.


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    Name:  IMG_20150526_144213.jpg
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Size:  13.3 KBCan anyone help?
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    (Original post by CD223)
    I'd have got it wrong in the exam. I initially thought -112g as the actual change in weight is -224g, and I saw it was initially 112g, so I did 112 - 224.


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    The same here, when i first thought about the question. I didn't realise when the current is off the scale reads zero


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    (Original post by huniibehi)
    Name:  IMG_20150526_144213.jpg
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    Name:  ImageUploadedByStudent Room1432649012.995558.jpg
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    Just done january 2012, im going through the papers in chronological order starting from 2010, I found this one a lot more difficult than the previous ones is anyone else the same? I still managed to get two marks of an A* but that was with about half an hours extra time hahaha! Anyone able to explain a couple of question, im still not sure on a few after seeing the mark scheme
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    (Original post by Leonacatherine)
    Just done january 2012, im going through the papers in chronological order starting from 2010, I found this one a lot more difficult than the previous ones is anyone else the same? I still managed to get two marks of an A* but that was with about half an hours extra time hahaha! Anyone able to explain a couple of question, im still not sure on a few after seeing the mark scheme
    The papers have been getting progressively harder. June 2014 MC was the hardest I've seen.

    Which questions are you referring to?


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    (Original post by CD223)
    The papers have been getting progressively harder. June 2014 MC was the hardest I've seen.

    Which questions are you referring to?


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    great -____- That sucks! I'd been feeling pretty confident before this paper
    There are a few im not sure on first was the multiple choice 15 I knew it had to be either c or d, normally i use ratios but because this was a force question its proportional to r^2 so i wasnt sure how to work it out
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    Also for question 3bii I dont get why you couldnt use the formula Vmax = 3 pi FA to work out the amplitude mark scheme required v =2pi f x square root A^2-x^2
    http://filestore.aqa.org.uk/subjects...W-QP-JAN12.PDF
    sorry was taking too long to upload images
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    (Original post by Leonacatherine)
    great -____- That sucks! I'd been feeling pretty confident before this paper
    There are a few im not sure on first was the multiple choice 15 I knew it had to be either c or d, normally i use ratios but because this was a force question its proportional to r^2 so i wasnt sure how to work it out
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    Question 15
    Name:  ImageUploadedByStudent Room1432651735.940124.jpg
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    (Original post by Leonacatherine)
    Also for question 3bii I dont get why you couldnt use the formula Vmax = 3 pi FA to work out the amplitude mark scheme required v =2pi f x square root A^2-x^2
    http://filestore.aqa.org.uk/subjects...W-QP-JAN12.PDF
    sorry was taking too long to upload images
    Sorry, what do you mean by the formula "Vmax = 3 pi FA"? Could you draw it out or type it in LaTex?


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