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Author Topic: Edexcel PHYSICS Doubts  (Read 136006 times)

Offline viktress

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Re: Edexcel PHYSICS Doubts
« Reply #720 on: June 20, 2011, 03:19:02 pm »
Phew! Thanks, I kept getting 650 N s however much I tried and I just couldn't figure it out. Now I'll be able to sleep tonight  :D
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Offline wakemeup

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Re: Edexcel PHYSICS Doubts
« Reply #721 on: June 20, 2011, 03:39:46 pm »
Quote from: Hermione Jean Granger on June 20, 2011, 12:31:15 pm
I am lost in 13b myself too. :(

Ok, Q16:

bi) Capacitor stores charge, as charge flows in during the charging process, pd is also formed.
If the voltage is constant, the capacitor will not discharge. The graph is during the charging process. Hence, pd is constant.
(remember: during discharging process, pd falls.)

ci) Use E= 1/2*C*V^2
(take voltage value from the graph)



cii) Compare the graph with the previous one and see the change in voltage value. (pd decreases)
Capacitor is initially charging from power supply then the capacitor is discharging exponentially.
(remember: the changing position of switches causes the discharge process, instead here. . . we added a power supply)

I hope that's clear. :)


Sorry, I'm still pretty lost. How does the capacitor keep the p.d constant? By discharging a constant pd? But the pd varies when the capacitor discharges. And if the capacitor is discharging exponentially why does the graph look like that? Could you please explain cii as well. (You explained bii where you wrote ci)

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Offline Romeesa-Chan

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Re: Edexcel PHYSICS Doubts
« Reply #722 on: June 20, 2011, 03:48:59 pm »
Quote from: wakemeup on June 20, 2011, 03:39:46 pm
Sorry, I'm still pretty lost. How does the capacitor keep the p.d constant? By discharging a constant pd? But the pd varies when the capacitor discharges. And if the capacitor is discharging exponentially why does the graph look like that? Could you please explain cii as well. (You explained bii where you wrote ci)



The pd is constant during the CHARGING process. That's cos the pd is equal to the emf of the source.

During discharging, the pd value falls as the charge decreases. (the capacitor decreases exponentially, we must just say that pd falls)

Sorry, if I am not making sense here.^^ :(

cii) T= RC
     R= T/C
     (value for capacitance is given and T value is taken from the graph)

:)
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Offline wakemeup

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Re: Edexcel PHYSICS Doubts
« Reply #723 on: June 20, 2011, 04:01:49 pm »
Quote from: Hermione Jean Granger on June 20, 2011, 03:48:59 pm
The pd is constant during the CHARGING process. That's cos the pd is equal to the emf of the source.

During discharging, the pd value falls as the charge decreases. (the capacitor decreases exponentially, we must just say that pd falls)

Sorry, if I am not making sense here.^^ :(

cii) T= RC
     R= T/C
     (value for capacitance is given and T value is taken from the graph)

:)

Thanks, I understand a bit better now but as for cii what value of T are we supposed to take? Because the mark scheme has 15-20 ms in it and I don't know how that came about.
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Offline Romeesa-Chan

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Re: Edexcel PHYSICS Doubts
« Reply #724 on: June 20, 2011, 04:05:11 pm »
Quote from: wakemeup on June 20, 2011, 04:01:49 pm
Thanks, I understand a bit better now but as for cii what value of T are we supposed to take? Because the mark scheme has 15-20 ms in it and I don't know how that came about.

That's good. :D
Lemme know if you don't.
For value of T, I took 16 ms. :)
« Last Edit: June 20, 2011, 04:29:37 pm by Hermione Jean Granger »
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Offline wakemeup

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Re: Edexcel PHYSICS Doubts
« Reply #725 on: June 20, 2011, 04:08:53 pm »
Quote from: Hermione Jean Granger on June 20, 2011, 04:05:11 pm
That's good. :D
Lemme know if you don't.
For value of T, I took 16 ms. :)


Yes, but how? Are you supposed to take a period, because that's about 10 and nowhere near the range in the mark scheme.
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Offline Romeesa-Chan

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Re: Edexcel PHYSICS Doubts
« Reply #726 on: June 20, 2011, 04:12:55 pm »
Quote from: wakemeup on June 20, 2011, 04:08:53 pm

Yes, but how? Are you supposed to take a period, because that's about 10 and nowhere near the range in the mark scheme.

Okay. This seems crazy but I tried it this way! (makes sense to me though)scratch that 16ms previously

See the previous graph: The time is constant from 8ms to 28 ms. The double peaks in the graph.

Time constant is always the same for every circuit. So we have 20ms for T value.

Does that make sense?
« Last Edit: June 20, 2011, 04:33:06 pm by Hermione Jean Granger »
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Offline Romeesa-Chan

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Re: Edexcel PHYSICS Doubts
« Reply #727 on: June 20, 2011, 04:36:01 pm »
Any more doubts? I will be leaving now. (:
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Offline wakemeup

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Re: Edexcel PHYSICS Doubts
« Reply #728 on: June 20, 2011, 04:43:08 pm »
Quote from: Hermione Jean Granger on June 20, 2011, 04:36:01 pm
Any more doubts? I will be leaving now. (:

No, but thanks for all your help. That is the only chapter that's still not super clear to me. I'll just keep my fingers crossed and hope they don't ask any super complex question from that (or any other chapter) tomorrow. 

Thanks again.
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Offline Dangerous99

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Re: Edexcel PHYSICS Doubts
« Reply #729 on: June 26, 2011, 07:58:08 pm »
Hey can somebody please help me out with physics unit 5?? ???
I dont get question 9 from june 2010 paper. It says For a black body radiator, the frequecy at which maximum radiation of energy occurs is proportional to?
a) T^-4
b) T^-1
c) T
d) T^4
« Last Edit: June 26, 2011, 08:18:30 pm by Dangerous99 »
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Offline Romeesa-Chan

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Re: Edexcel PHYSICS Doubts
« Reply #730 on: June 26, 2011, 08:33:46 pm »
Quote from: Dangerous99 on June 26, 2011, 07:58:08 pm
Hey can somebody please help me out with physics unit 5?? ???
I dont get question 9 from june 2010 paper. It says For a black body radiator, the frequecy at which maximum radiation of energy occurs is proportional to?
a) T^-4
b) T^-1
c) T
d) T^4

It says 'max frequency'

Max wavelength is proportional to 1 / T (Wien's law)

Frequency is proportional to 1 / wavelength, so it's proportional to T.

:D
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Offline Dangerous99

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Re: Edexcel PHYSICS Doubts
« Reply #731 on: June 26, 2011, 08:43:52 pm »
OH! Thanks it makes sense now  ;D
I was doing something like  FA = stephen boltsman equation heh heh  :-\
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Offline Romeesa-Chan

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Re: Edexcel PHYSICS Doubts
« Reply #732 on: June 26, 2011, 08:49:57 pm »
Quote from: Dangerous99 on June 26, 2011, 08:43:52 pm
OH! Thanks it makes sense now  ;D
I was doing something like  FA = stephen boltsman equation heh heh  :-\

No problem! :D
It's quite a tricky question which makes us jump to the answer immediately!
Any more doubts? (:
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Offline Dangerous99

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Re: Edexcel PHYSICS Doubts
« Reply #733 on: June 27, 2011, 12:25:52 am »
Quote from: Romeesa Chan on June 26, 2011, 08:49:57 pm
No problem! :D
It's quite a tricky question which makes us jump to the answer immediately!
Any more doubts? (:

No thanks :) inshallah well ace the exam tom  ;)
By the way i really like ur kuran kaname gif lol HAWT :P
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Offline Romeesa-Chan

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Re: Edexcel PHYSICS Doubts
« Reply #734 on: June 27, 2011, 02:06:12 am »
Quote from: Dangerous99 on June 27, 2011, 12:25:52 am
No thanks :) inshallah well ace the exam tom  ;)
By the way i really like ur kuran kaname gif lol HAWT :P

Insha Allah!!!!!!!!!! :D

OMGGGGGGGGGGGGGGGGGGGGGG. You watched VK?!!!!!!!!!! AWESOME STUFF. :D

Haha. Good luck !!!!!!!!!!! :D
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