Join TSR now and get all your revision questions answeredSign up now

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

    Offline

    1
    ReputationRep:
    this one was definitely harder than last year - we're so pressed for time in this exam its so annoying. gonna have to boss phya5
    Offline

    2
    ReputationRep:
    (Original post by QueNNch)
    Past grade boundaries:Attachment 425419

    I reckon
    51 for A
    57 for A*
    64/5 for 120 UMS?


    Posted from TSR Mobile
    Offline

    1
    ReputationRep:
    (Original post by NEWT0N)
    The graph was for discharing, so my analysis applies there
    But the point is, it was charged to that max current without that resistance and then discharged so the only thing R affects is the time taken to discharge
    Offline

    1
    ReputationRep:
    (Original post by Humbers)
    1. Is newtons as rate of change of momentum is force (newtons 2nd law)
    21. I put A as it had the longest side perpendicular to the magnetic field. Its a couple and not looking for flux (so largest area is irrelevant) force on couple is F=BIl so biggest couple was A as it had largest length perpendicular to field
    22. I think is 1/root 2 as kinetic energy is proportional to the square of velocity
    yes i agree
    Offline

    2
    ReputationRep:
    For Coulombs law, would I get any marks for quoting the formula and saying what each symbol meant?
    Offline

    9
    ReputationRep:
    (Original post by Fred Cantoni)
    64/5 for 120 UMS?


    Posted from TSR Mobile
    I hope you're right, last year it was 69/75 for 120 UMS
    Offline

    3
    ReputationRep:
    (Original post by chizz1889)
    Average I got 0.0475. Worked out what I was at 90• (0.0950) then divided by 2 ☺️ (Think I may have needed to divide by root2 though as I think RMS applies
    Nah I don't think you do. It's average because the rate of change of flux may not be constant, it's just the change in Nphi/ t


    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    (Original post by Will177)
    But the point is, it was charged to that max current without that resistance and then discharged so the only thing R affects is the time taken to discharge
    Please tell me what you don't understand about this:
    The voltage provided by the capacitor as it discharges is unchanged
    The resistance of the load is greater than before as it discharges
    Then just use V=IR like I showed to find the current in the discharging circuit
    Offline

    2
    ReputationRep:
    (Original post by Will177)
    But the point is, it was charged to that max current without that resistance and then discharged so the only thing R affects is the time taken to discharge
    V=IR the first basic law, V remains the same , R increases therefore I decreases
    Offline

    3
    ReputationRep:
    (Original post by Humbers)
    1. Is newtons as rate of change of momentum is force (newtons 2nd law)
    21. I put A as it had the longest side perpendicular to the magnetic field. Its a couple and not looking for flux (so largest area is irrelevant) force on couple is F=BIl so biggest couple was A as it had largest length perpendicular to field
    22. I think is 1/root 2 as kinetic energy is proportional to the square of velocity
    Yeah, newton is equal to acceleration.

    For 21 i meant the same thing. I have written the one with the greatest width
    22 asked for the ratio of the forces snd not velocity


    Posted from TSR Mobile
    Offline

    1
    ReputationRep:
    well I just lost my uni place for september!
    Offline

    2
    ReputationRep:
    (Original post by TheRAG)
    For Coulombs law, would I get any marks for quoting the formula and saying what each symbol meant?
    From past paper mark schemes, that's fine and you should get full marks
    Offline

    1
    ReputationRep:
    The Electric field strength should have been negative as the charge was negative. -1560 Vm^-1.

    I got this wrong.

    Also any clues on the damping question? I wrote there would be more damping without the ring as the total energy given to the system with the ring will be greater as GPE=mgh. The work done against air resistance is the same as time period is not affected - because the pendulum system has more energy with the ring it will take longer for the initial energy to be lost through doing work against air resistance. Thus the amplitude will decrease at a slower rate.
    Offline

    9
    ReputationRep:
    (Original post by TheRAG)
    For Coulombs law, would I get any marks for quoting the formula and saying what each symbol meant?
    Its possible but they said to write in words so its a 50/50 chance coz sometimes they allow formulas as long candidates write what each symbol means
    Offline

    0
    ReputationRep:
    (Original post by Fred Cantoni)
    No. It's force.


    Posted from TSR Mobile
    F=m(v-u)/t so I don't see how it can be force? Surely the unit of force is kgms^2, whereas momentum has a unit of kgms^1
    Offline

    2
    ReputationRep:
    (Original post by Amanzz)
    Nah I don't think you do. It's average because the rate of change of flux may not be constant, it's just the change in Nphi/ t


    Posted from TSR Mobile
    That's not the law for a rotating coil
    Offline

    2
    ReputationRep:
    For the capcitance and 2mj question did you guys get B (the energy taken from the battery was 2mj) that was incorrect and some energy would have been wasted so more energy was actually taken?
    Offline

    2
    ReputationRep:
    (Original post by ssargithan)
    21 A I put the same as you fro the same reason but people are saying B due to bigger area?
    Yes B had the biggest area. The force is only on the vertical pieces of the wire because the horizontal ones are parallel to the field and therefore experience no force. F=BIL with I=5 for all the currents. Then the couple is Fd-BILd=BI*Area of the rectangle. BI is constant so the couple is proportional to area of loop.
    Offline

    2
    ReputationRep:
    (Original post by Mehrdad jafari)
    Yeah, newton is equal to acceleration.

    For 21 i meant the same thing. I have written the one with the greatest width
    22 asked for the ratio of the forces snd not velocity


    Posted from TSR Mobile
    A newton is not the same unit as acceleration

    Force = newton = rate of change of momentum mv-mv/t = kgms-2
    Acceleration = rate of change of velocity = ms-2


    for 22. i know its the ratio but if it has half the kinetic energy it has root 2 of the velocity F=BQV so force is proportional to velocity
    Offline

    0
    ReputationRep:
    Surely A because the longest length was perpendicular to the field?
 
 
 
Poll
Which Fantasy Franchise is the best?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.