OCR PHYSICS B G494~ 11th June 2015 AM ~ A2 Physics

Original post by asdfghi

For the measuring of the decay constant question, could you put measure number of decays of a nucleus in a certain time and do decay constant equals the number of decays / time (in seconds) ?

I did something similar, but you'd need to divide by N too, since dN/dt = -decay constant x N.

The comments on here and in that unofficial mark scheme about drawing the decay curve and measuring gradient etc seem more logical though, not sure we'd get the mark.

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Reply 223

urz13

8

Original post by rapunzelsa

I said they were different, i tested it out with much higher values of T and lower values of p that still fitted with the pattern in the table, and it was definitely not constant, but i don't know what they wanted :-(

Who knows - we might get the benefit of the doubt :smile:

Reply 224

Rhetorical Hips

14

Original post by asdfghi

For the measuring of the decay constant question, could you put measure number of decays of a nucleus in a certain time and do decay constant equals the number of decays / time (in seconds) ?

That would give you activity though wouldn't it?

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Reply 225

MasterOfTheSwag

Original post by Mutleybm1996

The relationship wasn't true, they weren't all the same value

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I got numbers around the value 352 for each one so I said that it was constant, as the +-1 difference was negligible

Reply 226

OP

Original post by MasterOfTheSwag

I got numbers around the value 352 for each one so I said that it was constant, as the +-1 difference was negligible

That came up in one of the past papers
they were +-1 or 2 out too and I said they were constant, the mark scheme said otherwise, hence I said they're not proportional

Reply 227

username1200599

12

Original post by Robbo54

Ok for the natural log questions I divided the two values so you cancel the two constants, and re-arranged to get Epsilon, anyone do a similar method to this?

I equated the constants and that was how I managed to get the answer people have got.

Reply 228

OP

POLL ADDED

http://www.thestudentroom.co.uk/showthread.php?t=3397723

Reply 229

OP

Original post by Iridann

I equated the constants and that was how I managed to get the answer people have got.

Did you get the values as constant relationship or not?

I know I made some mistakes, but I don't think it's enough to cost me an A
Well, I hope not any way!

Reply 230

mariamaisabelle

Original post by rapunzelsa

I said they were different, i tested it out with much higher values of T and lower values of p that still fitted with the pattern in the table, and it was definitely not constant, but i don't know what they wanted :-(

I just wrote that it does work with the equation because they were all like 351, 352, 353 so they were all 350 to (2.s.f.) and the differences are just due to experiments always have error! or something like that anyway
but they probably accept it if you say it doesnt work with the equation as long as you justified why!!

Reply 231

ladygabriela97

Original post by Greating

This is what a friend and I think are acceptable answers, though there is some uncertainty in some of the longer explanation questions.

Our answers are attached.

Thanks for that!

I think i got most calculations right. The explanations i think could've gone better but overall made me feel a little more confident! :h:

Reply 232

malachirp

Original post by nair39

Only a mark lost for your conclusion I reckon. As long as your calculations were right you'd get those marks.

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I wouldn't give up hope of getting all those marks, often the markscheme accepts both as long as you explain why you came to your conclusion and it is valid. That being said i also said the relationship was true

Reply 233

saycell_96

Was the graph p against V

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Reply 234

OP

Original post by malachirp

I wouldn't give up hope of getting all those marks, often the markscheme accepts both as long as you explain why you came to your conclusion and it is valid. That being said i also said the relationship was true

you rounded to 2sf right, the data was to 3sf though

Reply 235

OP

Original post by saycell_96

Was the graph p against V

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P vs T
straight line through origin

Reply 236

OP

Original post by mariamaisabelle

I just wrote that it does work with the equation because they were all like 351, 352, 353 so they were all 350 to (2.s.f.) and the differences are just due to experiments always have error! or something like that anyway
but they probably accept it if you say it doesnt work with the equation as long as you justified why!!

you rounded to 2sf, but the data was to 3sf so you're being inaccurate here
I';m pretty sure it wasn't constant
I remember a question in another paper when they were close and it rejected them

Reply 237

nair39