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

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JaySP
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Original post by saad97

Sorry some are clearer than others
(edited 8 years ago)
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Original post by C-king
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Can someone pls help me on this have no clue:frown:


using E=0.5CV^2 derive two equations (leaving units in microfarads) so you get

3200 = CVsquared

800 = C(V-2)squared

you got two simultaneous divide first eqn by V and the sub into 2 hence you get v = 4 and then get C from eqn 1 again (although I would rather stick with plotting each of those 4 answers in the eqn and check by verification)
Original post by C-king
BUMP


May have been answered, Is the answer B?
Original post by samlyon
Anyone? I'm just confusing myself


Think about moving a spring very slowly. You'd barely be affecting the oscillations which is what its getting at with 0.2 Hz.

1.5hz is resonance as its the same as the natural frequency.

As for 10Hz, you must remember those resonance curves, right? Think of what happens to the amplitude as the driver frequency exceeds the natural frequency.

Edit: I didn't pay attention to your question. When in resonance , the driver and the displacement of the oscillation system are 90 degrees out of phase. It's just a fact.
(edited 8 years ago)
Are we allowed Graphics calculators in the physics exams? :smile:
Original post by AnneOldman
Does anyone know any examples of the different types of damping?

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Light damping:
person on a swing

Heavy damping:
used in some earthquake proof buildings

Critical damping:
used in suspension systems, i.e shock absorbers

Hopefully this helped.

:smile:
Original post by JaySP
Impulse=∆momentum=kgms-1=Ns


Thanks mate is there ever a unit kgms-2


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Someone give me a question they can't do, multiple choice is my favourite!
Original post by Mattyhouse
Are we allowed Graphics calculators in the physics exams? :smile:


why would you need one?
Original post by AR_95
Don't ever think that with MC. It can vary from plugging into an equation without doing any work, to 3 or 4 step questions

well atleast I learnt that now and not in the exam
Reply 3730
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JaySP
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Original post by gcsestuff
Thanks mate is there ever a unit kgms-2


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Yes, rate of change of momentum (Also known as force)/
Original post by Mattyhouse
Are we allowed Graphics calculators in the physics exams? :smile:


Yes
Original post by Sbarron



Yeah I totally get the part where emf is max at 90 to field/flux lines as they are perpendicular and more are being cut.... But to me that is the same as maximum flux linkage as it's where the most flux is being cut!But I obviously can't see the difference between maximum flux linkage and maximum flux apart from the number of loops are considered!???!And maths explanations won't help I don't do alevel maths and didn't do GCSEs for years so Ihave only leant the basic physics maths skills

It's not really about whether you are doing maths or not. I'm doing a level maths too but i still haven't applied that maths anywhere in physics. The maths does help but that's where we have an idea of what's going on and not where we have no idea, lol


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Original post by davidharris96
May have been answered, Is the answer B?


yeh
Hi, quick question, if anyone could answer it for me, it would be a great help!!
Why in a MS does it say E proportional to V squared in the equation of energy stored in a capacitor? Why can't you use V is proportional to E because of the equation: E=0.5QV? How do you now what equation to use when working out what is proportional to what in the energy equations?



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Original post by samlyon
Anyone? I'm just confusing myself


The natural frequency is 1.5Hz.

When the frequency of the driver is equal to the natural frequency 2)(b)(ii), the phase difference is pi/2, i.e. in phase with velocity. At 0.2Hz (i), the phase difference is nearly zero. At 10Hz(iii) the phase difference is nearly pi

In general:
when driven at freq much lower than natural: little or no phase difference
when driven at resonance: phase difference pi/2
driven at frequency much higher than resonance: phase difference approaching pi.

I'm afraid I can't explain why this is the case, so unless someone else can it's just something to blindly accept.
Original post by AR_95
why would you need one?


you wouldnt, just saves time with solving quadratics ( i assume this is why he wants to know )
Original post by Brianna96
Hi, quick question, if anyone could answer it for me, it would be a great help!!
Why in a MS does it say E proportional to V squared in the equation of energy stored in a capacitor? Why can't you use V is proportional to E because of the equation: E=0.5QV? How do you now what equation to use when working out what is proportional to what in the energy equations?



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because technically if the pd is changing so is the charge, its only the capacitance tthat remains constant
Original post by AR_95
why would you need one?


My normal calculator keeps going on and off, its ****ed :s not sure whether just to use my graphic instead ;/
How to work out when a set of swings of varying time period will next be "in conjunction"?

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