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

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Original post by AR_95
Im all set for the MC, but not prepared at all for any 6 markers..


You'll be okay! I'm scared for multiple choice.. they just mess us up sometimes. -_-

6 marks will be something from the past papers or something totally new..
Question 1c) june 2013 phya4/2 ? Help much appreciated as I never know how to do these

http://filestore.aqa.org.uk/subjects/AQA-PHYA4-2-QP-JUN13.PDF
Original post by aprocrastinator
could someone explain this question please? I've seen several of these questions come up before and I just don't get them. Like why would the sides attract each other??


is the answer B, because the currents are parallel to the field
Original post by CD223
They're respectively defined as the force per unit mass/charge exerted on a test mass in the field.


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ahh okay - thank you! :smile:
Original post by _Caz_
No AQA for me. was a terrible paper. pretty sure about 8 marks of it were not even on the specification...


Ah that sucks. Ours was absolutely horrific as well, fingers crossed for really low boundaries.

Original post by Mattniemier
Is anyone else revising from the CGP guide rather than the nelson thornes book


You can use it alongside classnotes, but if you mean the revision guide it doesn't actually have everything in so be aware of this!
Original post by CD223
PQ and RS is where current (therefore charges) is parallel to magnetic field lines so no force is experienced on them


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Thank you :smile: I really hope I don't make stupid mistakes in this paper I need to get as high as UMS as possible!
Original post by aprocrastinator
could someone explain this question please? I've seen several of these questions come up before and I just don't get them. Like why would the sides attract each other??


If you don't mind me asking, what year paper is this question from?
Original post by Adangu
Question 1c) june 2013 phya4/2 ? Help much appreciated as I never know how to do these

http://filestore.aqa.org.uk/subjects/AQA-PHYA4-2-QP-JUN13.PDF


Lowest common multiple which is 38s. After each oscillation of the 2s pendulum the 1.9s pendulum become 0.10s more out of phase. So after 20 cycles, the phase difference between the 2s pendulum and the 1.9s pendulum becomes 2s. As this is equal to the 2s pendulum's time period, they are back in phase (in the same way that for any waveform 2pi out of phase is the same as being in phase)
Original post by Adangu
Question 1c) june 2013 phya4/2 ? Help much appreciated as I never know how to do these

http://filestore.aqa.org.uk/subjects/AQA-PHYA4-2-QP-JUN13.PDF


Take the period of one and divide by the difference in period, usually works
I don't understand how the induced emf (rate of Change of flux) is max when the flux through it is zero!?
So do we always use the lowest significant figure from the question in the final answer?
Original post by Sbarron
I don't understand how the induced emf (rate of Change of flux) is max when the flux through it is zero!?


If you do AS or A level maths, it's because differentiating cosx gives (-)sinx. Otherwise it's because (maximum flux- current flux) is greatest when current flux= 0. Hence emf= (maximum flux- current flux)/time is greatest
Original post by Sbarron
I don't understand how the induced emf (rate of Change of flux) is max when the flux through it is zero!?


imagine the flux changing as a sin wave as a coil rotates. the derivative of a sine wave is cosine, ie pi/2 out of phase. when a sine wave is zero its gradient is max and when its at max and min its gradient is zero. Its the rate of change of flux not actually the flux itself
Original post by HenryHein
Lowest common multiple which is 38s. After each oscillation of the 2s pendulum the 1.9s pendulum become 0.10s more out of phase. So after 20 cycles, the phase difference between the 2s pendulum and the 1.9s pendulum becomes 2s. As this is equal to the 2s pendulum's time period, they are back in phase (in the same way that for any waveform 2pi out of phase is the same as being in phase)


Original post by DanielWall96
Take the period of one and divide by the difference in period, usually works


Thank you guys so much. So basically

Work out difference between time period = 0.1

Take the longer time period and divide by it 2/0.1= 20

Times this by the shorter time period 1.9 x 20 = 38s

Cheers!
Original post by michaelotty
So do we always use the lowest significant figure from the question in the final answer?


Only have to if they ask you to. Of course it is good general practice to do so anyway.
Can someone explain why Q14 is A? i thought it was B?...

http://www.egsphysics.co.uk/files/a_level_past_papers/Jun02/AQA-PA04-W-QP-Jun02.pdf
Original post by Sbarron
I don't understand how the induced emf (rate of Change of flux) is max when the flux through it is zero!?


When the magnetic flux linkage through the rectangular coil is 0 ( parallel to the magnetic field) then the induced emf would be maximum because the rectangular coil would cut most of the field lines perpendicularly at this position.
Does anyone know how to go about answering this question? I got A but the answer is B.
Original post by Boop.
Can someone explain why Q14 is A? i thought it was B?...

http://www.egsphysics.co.uk/files/a_level_past_papers/Jun02/AQA-PA04-W-QP-Jun02.pdf


Because the magnetic field lines are not passing through the charged particles at RIGHT ANGLES. Therefore, the magnetic force would not act where the particles would move unaffected.
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Deddy
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Original post by Boop.
Can someone explain why Q14 is A? i thought it was B?...

http://www.egsphysics.co.uk/files/a_level_past_papers/Jun02/AQA-PA04-W-QP-Jun02.pdf


The electron is travelling parallel to the magnetic field, so the force on the electron is 0.

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