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

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Thanks!

Essentially you know it always takes 36ms for V to halve in value. This is because, for exponential decay the same decrease is observed over equal time intervals.

As E is proportional to V squared, this means that when E becomes E/16, V must have halved again to become V/4.

This means that the time for V to halve twice from its initial value and therefore become V/4 is:

36ms + 36ms = 72 ms

Does that help?

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Thanks

This would be the best way to approach that question because the change in voltage is an exact multiple of the voltage at 36 ms.
I don't examiners will give inexact values so yeah, this is the easiest way to get the answer :smile:

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Reply 2681

CD223

Original post by Mehrdad jafari

Thanks

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Thank my teacher lol.

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Reply 2682

Disney0702

Original post by Mehrdad jafari

Oh, sorry, i meant to write 72ms as i worked with ms in the question.
And yeah, you're correct in saying that you cannot assume the proportionality of t with C as C is constant, but this proportionality has a different sense. t is proportional to c means that the greater the capacitance the longer the time the capacitor takes to discharge as it can contain more charge. I needed that proportionality to see how the voltage varies with time. If, for example, the greater the capacitance the less time it would take to discharge then proportionally would differ. It would become :
ImageUploadedByStudent Room1433590500.968169.jpg

ImageUploadedByStudent Room1433590500.968169.jpg

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Ah okay, I understand.

Thank you :smile:

Reply 2683

Disney0702

Original post by getback339

yeah thanks for the reply, im not too sure i get the difference between A and B though

Graph A shows that as frequency increases toward the natural frequency the amplitude decreases and Graph B shows that as frequency increases towards natural frequency the amplitude increases.

Graph A's story is incorrect so it has to be Graph B.

Does that help?

Reply 2684

Disney0702

Original post by Jed-Singh

Can anyone help me with the multiple choice questions that involve 'when potential or field strength etc' equals 0. I never get them correct :frown:

Do you have an example question, it'd be easier to explain.

Reply 2685

coqthepoliceman

can someone help with q15 in mc section of the june 2014 paper?

Reply 2686

Jed-Singh

Original post by Disney0702

Do you have an example question, it'd be easier to explain.

June 2013 Q13 :smile:

Reply 2687

gcsestuff

Original post by coqthepoliceman

can someone help with q15 in mc section of the june 2014 paper?

ImageUploadedByStudent Room1433592670.383319.jpg

This is how I did it.

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Reply 2688

Disney0702

Original post by Jed-Singh

June 2013 Q13 :smile:

Does that help?

Reply 2689

Jed-Singh

Original post by Disney0702

Does that help?

X=d-y! Youre a genius, i never thought of doing that. Thanks so much :smile:

Reply 2690

Disney0702

Original post by Jed-Singh

X=d-y! Youre a genius, i never thought of doing that. Thanks so much :smile:

You're welcome :smile:

Reply 2691

Lau14

Original post by Disney0702

Thank you so much Lauren! :smile:

I've definitely never seen this before! Had you never uploaded this I would've probably freaked out in the exam hall.

And the attachment you released is in good condition. :wink:

Oh good, it worked then (stupid internet!). No problem, it's a little worrying how many teachers don't bother mentioning this at all - our teacher is virtually useless and even he managed to give us them! :smile:

Reply 2692

getback339

Original post by Disney0702

oh yeah haha, just confused there, thanks anyway

Reply 2693

Disney0702

Original post by getback339

oh yeah haha, just confused there, thanks anyway

You're welcome

Reply 2694

Disney0702

Can someone explain something to me please.

Q8 Jan '08

I understand that the answer is C but I do not see how D could be incorrect.

Reply 2695

a.a.k

Original post by Disney0702

Can someone explain something to me please.

Q8 Jan '08

I understand that the answer is C but I do not see how D could be incorrect.

C=Q/V

Which basically a graidient of this graphs.
So X has greater gradient than Y.
So Y has less gradient than X so less capacitance

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Reply 2696

Adangu

Original post by Disney0702

Can someone explain something to me please.

Q8 Jan '08

I understand that the answer is C but I do not see how D could be incorrect.

C=Q/V

For Y, The p.d is larger than the charge. Shown by a smaller gradient. So capacitance isn't increasing.

Reply 2697

CD223

Original post by Disney0702

Can someone explain something to me please.

Q8 Jan '08

I understand that the answer is C but I do not see how D could be incorrect.

The gradient of the graph is representative of the capacitance. As X has a greater gradient, its capacitance is greater.

Both are straight lines - in other words the gradient, and hence the capacitance is constant for both.

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Reply 2698

Adangu

Original post by CD223

Thank my teacher lol.

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Hey man, hows it going?

When we were discussing about the six markers a while back you said you thought it would be on SHM or circular motion. If the six marker is on SHM, what do you think they will ask? or like what would they be looking to see in your answers?

Reply 2699

Disney0702

Original post by a.a.k

C=Q/VWhich basically a graidient of this graphs.So X has greater gradient than Y.So Y has less gradient than X so less capacitancePosted from TSR Mobile

Original post by Adangu

C=Q/V

For Y, The p.d is larger than the charge. Shown by a smaller gradient. So capacitance isn't increasing.