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

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Original post by CD223
The general equation for the induced emf is:

[br]ϵ=BANωsin⁡(ωt)[br][br]\displaystyle \epsilon = BAN \omega \sin (\omega t)[br]

Due to the nature of the sinusoidal variation in emf (when sin⁡(ωt)=1\displaystyle \sin (\omega t) = 1), its peak value is:

[br]ϵ0=BANω[br][br]\displaystyle \epsilon_0 = BAN \omega[br]

As ω=2πf\displaystyle \omega = 2 \pi f, and flux linkage is equivalent to =BAN\displaystyle = BAN:

Dividing both sides by omega gives the max flux linkage equal to:

[br]BANMax=ϵ0ω[br][br]\displaystyle BAN_{Max} = \dfrac{\epsilon_0}{\omega}[br]

[br]∴BANMax=ϵ02πf[br][br]\displaystyle \therefore BAN_{Max} = \dfrac{\epsilon_0}{2 \pi f}[br]


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Original post by CD223
The general equation for the induced emf is:

[br]ϵ=BANωsin⁡(ωt)[br][br]\displaystyle \epsilon = BAN \omega \sin (\omega t)[br]

Due to the nature of the sinusoidal variation in emf (when sin⁡(ωt)=1\displaystyle \sin (\omega t) = 1), its peak value is:

[br]ϵ0=BANω[br][br]\displaystyle \epsilon_0 = BAN \omega[br]

As ω=2πf\displaystyle \omega = 2 \pi f, and flux linkage is equivalent to =BAN\displaystyle = BAN:

Dividing both sides by omega gives the max flux linkage equal to:

[br]BANMax=ϵ0ω[br][br]\displaystyle BAN_{Max} = \dfrac{\epsilon_0}{\omega}[br]

[br]∴BANMax=ϵ02πf[br][br]\displaystyle \therefore BAN_{Max} = \dfrac{\epsilon_0}{2 \pi f}[br]


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What do you mean by the sinusoidal variation of emf?, is sinwt=1 after one full cycle?
Original post by CD223
Is anyone revising AS stuff?


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I hope they don't bring any AS in the exam :frown:

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Original post by TALAKHAN
What do you mean by the sinusoidal variation of emf?, is sinwt=1 after one full cycle?


The emf varies as a sine wave. At its peak, sin⁡(ωt)\sin (\omega t) is at a maximum (ie: it equals 1). This gives the largest possible value of ϵ\epsilon.

The emf is cyclical in nature - it peaks in regular intervals, so there will always be the same amount of time elapsing between peaks.


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Original post by _Caz_
I hope they don't bring any AS in the exam :frown:

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They sometimes questions about hookes laws and spring extension


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Original post by CD223
It's a uniform electric field so the potential varies linearly.

[br]E=ΔVΔd=2.0V0.6m[br][br]E = \dfrac{\Delta V}{\Delta d} = \dfrac{2.0V}{0.6m}[br]

[br]⇒E=3.33Vm−1 (3 sf)[br][br]\Rightarrow E = 3.33 Vm^{-1}\ \text{(3 sf)}[br]


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Cheers, you're a god really. I was confused because I didn't know if it was Delta V or just V, but was doing it in exam conditions so wasnt able to check.
So E would be 2/0.6 as you've said, but would the potential then be 2 at the midpoint?


I can't seem to get the right answer for this one,

I tried using the F = QQ/4piEoR^2 but it doesnt work, why?

(edited 8 years ago)
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Original post by AR_95
Cheers, you're a god really. I was confused because I didn't know if it was Delta V or just V, but was doing it in exam conditions so wasnt able to check.
So E would be 2/0.6 as you've said, but would the potential then be 2 at the midpoint?


I can't seem to get the right answer for this one,

I tried using the F = QQ/4piEoR^2 but it doesnt work, why?



Yeah the potential would be 2.0V midway between the two as the field is uniform so the same change in potential is observed over equal distances.

In that question it's asking for the gravitational force of attraction. In other words, you'd use:

[br]F=GMpMer2[br][br]\displaystyle F = \dfrac{GM_pM_e}{r^2}[br]


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Original post by CD223
Yeah the potential would be 2.0V midway between the two as the field is uniform so the same change in potential is observed over equal distances.

In that question it's asking for the gravitational force of attraction. In other words, you'd use:

[br]F=GMpMer2[br][br]\displaystyle F = \dfrac{GM_pM_e}{r^2}[br]


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Yet again just me failing to read the question :frown:

I did the same with another part where I used diameter instead of radius, it's going to affect me :s-smilie:

Hopefully all these mistakes is because of the burnout of revising every day, and in the exam i'll do better with a fresh mind lol
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Original post by AR_95
Yet again just me failing to read the question :frown:

I did the same with another part where I used diameter instead of radius, it's going to affect me :s-smilie:

Hopefully all these mistakes is because of the burnout of revising every day, and in the exam i'll do better with a fresh mind lol


Yeah, just read the question twice before attempting it - it takes longer but is more effective :smile:


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Original post by _Caz_
I hope they don't bring any AS in the exam :frown:

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They will do - PHYA4 is a synoptic unit, which means previous content will be tested in it. It's usually only in a very small way (2 marks maybe).
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Original post by Lau14
They will do - PHYA4 is a synoptic unit, which means previous content will be tested in it. It's usually only in a very small way (2 marks maybe).


Personally I think it's really harsh. Other A levels don't test anything from AS.


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Original post by CD223
Personally I think it's really harsh. Other A levels don't test anything from AS.


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They do, actually! Chemistry requires ongoing knowledge to be able to do the A2 stuff, and they do occasionally put in questions that are purely AS based. Maths is obviously constantly building on AS stuff, and apparently biology is absolutely awful for it - because of the essay questions and some other bits, you basically need to know the entire of AS. Almost all subjects do it I think, these are just the ones I know a bit about :smile:
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Original post by Lau14
They do, actually! Chemistry requires ongoing knowledge to be able to do the A2 stuff, and they do occasionally put in questions that are purely AS based. Maths is obviously constantly building on AS stuff, and apparently biology is absolutely awful for it - because of the essay questions and some other bits, you basically need to know the entire of AS. Almost all subjects do it I think, these are just the ones I know a bit about :smile:


Sorry yeah when I said other subjects I basically meant the only others I do :P besides obviously maths, history and computing are totally separate -,-


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Original post by gcsestuff
They sometimes questions about hookes laws and spring extension


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Physics 2 stuff is okay. Physics 1 is where my worry lies. I can't remember anything aside from debroglie wavelength :frown:

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Original post by _Caz_
Physics 2 stuff is okay. Physics 1 is where my worry lies. I can't remember anything aside from debroglie wavelength :frown:

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Lol there's not much else I'd assume they could ask you about particle stuff?


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How would you answer question 9 on the multiple choice part of the jan 2013 paper
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Original post by SuperMushroom
How would you answer question 9 on the multiple choice part of the jan 2013 paper


ImageUploadedByStudent Room1433441793.561546.jpg


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Original post by CD223


Thanks! Do you have these model answer cards for every multiple choice question?
Original post by CD223
Lol there's not much else I'd assume they could ask you about particle stuff?


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True. Maybe they could put it in the energy mass part of unit 5 though. :s

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Original post by SuperMushroom
Thanks! Do you have these model answer cards for every multiple choice question?


Nope lol, unfortunately not. When people ask questions on the thread I just quickly grab a pen and paper and post my workings :smile: sorry!


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Original post by _Caz_
True. Maybe they could put it in the energy mass part of unit 5 though. :s

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I swear that's illegal.

(It's not, but you know what I mean :tongue:)

I think the stress/strain topic is worth revising along with waves from last year as they seem to come up in SHM questions in the past.


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