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# OCR Physics B - G491 (Physics in Action) January 2012

Physics exam discussion - share revision tips in preparation for GCSE, A Level and other physics exams and discuss how they went afterwards.

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1. Re: OCR Physics B - G491 (Physics in Action) January 2012

H D^2 l/4 pi R -which value had the most uncertainty

My thinking was d^2 because if you square a value the uncertainty on the top decreases,over a small uncertainty on the bottom.

I know a lot of people put R but does anyone know what the right answer is here
2. Re: OCR Physics B - G491 (Physics in Action) January 2012
(Original post by sfalcini1)
in our class half of us did your way and the other did a different way. I ended up doing what you did finding 2.3V across other resistor , and as we had the resistance and V across one resistor , i worked out the current as it is the same across both components (series circuit) , then knowing V for both , i worked out R for the resistor which the resistance we were not given and got something like 1300 ohms ??

I reckon sadly however you worked out the ohm rating for the 3.7V across the resistor,I think you needed to work out the 2.3/6 v resistor using the graph

1300/2100 x 6 = 3.7

I got 500 personally although that could quite obviously be wrong

500/1300 x 6=2.3
3. Re: OCR Physics B - G491 (Physics in Action) January 2012
(Original post by KING2011BOB)

H D^2 l/4 pi R -which value had the most uncertainty

My thinking was d^2 because if you square a value the uncertainty on the top decreases,over a small uncertainty on the bottom.

I know a lot of people put R but does anyone know what the right answer is here
I think it was D, but because it had the largest percentage uncertainty in it's measurement, rather than it being squared. Not 100% sure though, the numbers threw me off a little bit.
4. Re: OCR Physics B - G491 (Physics in Action) January 2012
(Original post by KING2011BOB)
I reckon sadly however you worked out the ohm rating for the 3.7V across the resistor,I think you needed to work out the 2.3/6 v resistor using the graph

1300/2100 x 6 = 3.7

I got 500 personally although that could quite obviously be wrong

500/1300 x 6=2.3
Yep your way sounds right , Hopefully i still get marks for working out , and thanks for the clearing up.
5. Re: OCR Physics B - G491 (Physics in Action) January 2012
(Original post by KING2011BOB)
I reckon sadly however you worked out the ohm rating for the 3.7V across the resistor,I think you needed to work out the 2.3/6 v resistor using the graph

1300/2100 x 6 = 3.7

I got 500 personally although that could quite obviously be wrong

500/1300 x 6=2.3
So did you get like 497 Ohms for your answer because that is why got, I think I used the same method as you.
6. Re: OCR Physics B - G491 (Physics in Action) January 2012
(Original post by Matt G)
So did you get like 497 Ohms for your answer because that is why got, I think I used the same method as you.
I got 511 but it was one of those questions which will have a boundary from 485-515 I would say-either way still get working marks

Did anyone get for the question just after the emf prove question

The value of the resistor to be 6 ohms-I reckon this was rite
7. Re: OCR Physics B - G491 (Physics in Action) January 2012
can someone please post the paper with the mark scheme??
8. Re: OCR Physics B - G491 (Physics in Action) January 2012
hey,

can someone email me the paper and the mark skeme please?

Last edited by Loz17; 16-04-2012 at 18:56.
9. Re: OCR Physics B - G491 (Physics in Action) January 2012
(Original post by Speccysteve)
hey,

can someone email me the paper and the mark skeme please?

Did you manage to get hold of the paper?
Im tryna make sure i can get all the past papers done in preperation for my exam , ,would be really grateful if anyone could send it to me, thanks
10. Re: OCR Physics B - G491 (Physics in Action) January 2012
11. Re: OCR Physics B - G491 (Physics in Action) January 2012
(Original post by cloudhang)
They are on the OCR website for this exam.

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