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

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    (Original post by gcsestuff)
    Using flemings left hand rule, am i right in thinking the current finger is always in the direction of current, so for example if an electron is going right in a magnetic field, the conventional current and therefore my 2nd finger would be pointing left.
    Yeah that's correct!


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    (Original post by chughes17)
    Yeah that's correct!


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    THANKS!!
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    (Original post by gcsestuff)
    Using flemings left hand rule, am i right in thinking the current finger is always in the direction of current, so for example if an electron is going right in a magnetic field, the conventional current and therefore my 2nd finger would be pointing left.
    Yup.

    The second finger points in the direction of conventional current


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    (Original post by CD223)
    

\text{Mass of container}=0.65kg

    The balance will read:

    

0.65kg + \text{Mass of sand after 10s}

+ \text{Mass equivalence of force due to sand falling}

    

\text{Mass of sand after 10s} =

    

0.3kgs^{-1} \times 10s

    

= 3.00kg

    

\text{Mass equivalence of force due to sand falling} = \dfrac{\text{Force of sand}}{g}

    

= \dfrac{\text{Momentum per second}}{9.81}

    

= \dfrac{1.68}{9.81}

    

= 0.17kg

    Therefore, the balance reads:

    

0.65kg + 3.00kg + 0.17kg

    

= 3.82kg
    Thank you, just one question, how did you form the first equation?
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    (Original post by saad97)
    Thank you, just one question, how did you form the first equation?
    The one about what the balance reads?


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    (Original post by CD223)
    The one about what the balance reads?


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    Yes, are we just supposed to know to include the mass equivalence of force due to sand falling?
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    Can I ask what university you're going too CD223? Is it Oxford or Cambridge?

    Please prepare to tell everyone what you got as an answer for the questions once we do this exam.. because your exam paper will essentially be the mark scheme
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    Do we need to know unit 2 waves for unit 4? (See Q5C here: http://filestore.aqa.org.uk/subjects...W-QP-JAN11.PDF )
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    (Original post by saad97)
    Yes, are we just supposed to know to include the mass equivalence of force due to sand falling?
    I didn't at first, but I imagined the sand that falls right at 10s causing the scales to show a slightly bigger reading than the mass of the sand+container alone. (Imagine jumping on a scale.)
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    Any tips on how to answer the 6 marker
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    I'm stuck on how to do these two questions.

    Attachment 410565410567
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    (Original post by PotterPhysics)
    Do we need to know unit 2 waves for unit 4? (See Q5C here: http://filestore.aqa.org.uk/subjects...W-QP-JAN11.PDF )
    Technically, you can be tested on any units prior to the one you are sitting in the exam; this question (relates to unit 4 resonance as well unit 2 waves) is likely to be the only one of its type in a paper.

    (Original post by dominicwild)
    I'm stuck on how to do these two questions.

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    Q.14 - The gravitational potential (V) is proportional of the planet's mass (M) and inversely proportional of the planet's radius (r) following the equation: V=-GM/r. If r (diameter/2) is multiplied by 1/2, and M is multiplied by 1/10, then V is multiplied by 1/10 and 2/1

    -63 x (1/10) x (2/1) = -12.6 [A]
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    an anyone show mne working to june 2010 question 8. Its a quick question and Ive got the right answer I just dont think ive worked it out right. Thanks
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    Also can someone help me with june 2010 question 14
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    (Original post by saad97)
    Yes, are we just supposed to know to include the mass equivalence of force due to sand falling?
    We can work that out by dividing the force (momentum per second impacting on the balance) by g.


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    (Original post by EmiratesCaptain)
    Can I ask what university you're going too CD223? Is it Oxford or Cambridge?

    Please prepare to tell everyone what you got as an answer for the questions once we do this exam.. because your exam paper will essentially be the mark scheme
    Hahaha, I'm flattered, but no. I got rejected by Oxford after my interview in December. Being totally honest, I'm happy about it because I don't think the atmosphere would have been healthy for me - I need a place I feel I can chill out!

    I'm (hopefully) going to Bath to do Computer Science in September. How about you?


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    (Original post by PotterPhysics)
    Do we need to know unit 2 waves for unit 4? (See Q5C here: http://filestore.aqa.org.uk/subjects...W-QP-JAN11.PDF )
    It's more testing resonance than waves, but I do see your point. I think it's worth going over some AS stuff - particles for PHYA5 and Mechanics/Materials/Waves for this paper.


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    (Original post by Fvthoms)
    Technically, you can be tested on any units prior to the one you are sitting in the exam; this question (relates to unit 4 resonance as well unit 2 waves) is likely to be the only one of its type in a paper.



    Q.13 - The gravitational field strength (g) is inversely proportional to the square of the planet's radius (r) following the equation: g=GM/r^2. If r (diameter/2) is multiplied by 100, g is multiplied by 1/100^2.

    800/100^2=0.0008 [A]

    Q.14 - The gravitational potential (V) is proportional of the planet's mass (M) and inversely proportional of the planet's radius (r) following the equation: V=-GM/r. If r (diameter/2) is multiplied by 1/2, and M is multiplied by 1/10, then V is multiplied by 1/10 and 2/1

    -63 x (1/10) x (2/1) = -12.6 [A]
    (Original post by dominicwild)
    I'm stuck on how to do these two questions.

    Attachment 410565410567
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    Here is PotterPhysics' answer to the first question: The answer is 800 (C)

    http://www.thestudentroom.co.uk/show...9#post56268219

    And the second one comes out to be -13 (A) as above


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    (Original post by gcsestuff)
    an anyone show mne working to june 2010 question 8. Its a quick question and Ive got the right answer I just dont think ive worked it out right. Thanks
    For a simple pendulum:
    

T = 2 \pi \sqrt{\dfrac{l}{g}}

    This follows that:
    

T = \propto l

    For a mass on a spring:
    

T = 2 \pi \sqrt{\dfrac{m}{k}}

    This follows that:
    

T = \propto m

    That means if we double l and halve m then the period of the pendulum will be twice that of the spring.



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    (Original post by gcsestuff)
    Also can someone help me with june 2010 question 14
    I had workings for this a few pages back

    Potential is a scalar. You use scalar addition to work out total potential at a point in an electric field.

    

V = \dfrac{Q}{4 \pi {\epsilon_0} r}

    Due to the geometry of the square, each charge in this instance is at a distance of r = \sqrt{2} a from point P.

    See my workings below:
    Name:  ImageUploadedByStudent Room1432804311.429359.jpg
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Size:  72.5 KB


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