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Physics Exams and the Accuracy of your answers. Watch

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    So, we're getting really close to exam time again and for the second time in my A-level career I find myself wondering about the answer tolerances OCR places on questions in their physics exams.

    I don't know about you, but I've been caught out many times by giving my answers to too many decimal places/significant figures. I think that perhaps the time has come we get to the bottom of, what I believe to be rather puzzling, problem.

    I know from numerous discussions with teachers and fellow physics students that the general consensus is to give answers according to the WEAKEST accuracy strength value used in calculations. E.g. in a questions using, lets say, 1 value to 2d.p., another value to 3d.p. and the final value to 1d.p. we give our answer to 1d.p.

    However, do we loose marks for giving TOO accurate answers if perhaps we are mistaken? I've seen no mention as to the answer in the mark schemes or even the examiners reports (which, by the way, I recommend reading.). So what does TSR Physics Student community think?

    Cheers,

    Beaneebar
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    (Original post by Beaneebar)
    So, we're getting really close to exam time again and for the second time in my A-level career I find myself wondering about the answer tolerances OCR places on questions in their physics exams.

    I don't know about you, but I've been caught out many times by giving my answers to too many decimal places/significant figures. I think that perhaps the time has come we get to the bottom of, what I believe to be rather puzzling, problem.

    I know from numerous discussions with teachers and fellow physics students that the general consensus is to give answers according to the WEAKEST accuracy strength value used in calculations. E.g. in a questions using, lets say, 1 value to 2d.p., another value to 3d.p. and the final value to 1d.p. we give our answer to 1d.p.

    However, do we loose marks for giving TOO accurate answers if perhaps we are mistaken? I've seen no mention as to the answer in the mark schemes or even the examiners reports (which, by the way, I recommend reading.). So what does TSR Physics Student community think?

    Cheers,

    Beaneebar

    As far as I'm aware, there is one question on each paper that specifically tests your use of significant figures. It will state in the question that you are to use an appropriate number. There will be one mark given for this. In other questions you will not be tested. You can therefore only lose one mark per paper if you get this wrong.
    In general you are correct to use the least number of sig figs in the data provided when presenting your answers to a numerical problem.
    If in doubt use 2 or 3 figs.

    The exam board spec should state this but it's often difficult finding this info.
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    The way it works is that sig figs are relevant in most numerical questions BUT you only get penalised once even if you get it 'wrong' several times.

    As a general rule you wont get penalised if you use 2 or more - BUT every digit you give has to be correct. You can give 8 sf answers without penalty but all 8 digits have to be spot on ie no rounding.
    You get penalised for using 1sf answers.
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    So, I was doing a paper (Jan 2011) Newtonian World and I come across this question:

    Q:
    Name:  Screen Shot 2014-04-27 at 15.08.33.png
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    A:
    Name:  Screen Shot 2014-04-27 at 15.06.34.png
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    In my answer, I did exactly this only giving the answer as 2.9*10^7 as 6.0*10^24 is only to 2sig.figs./1.d.p..

    Why do I lose a mark for that?

    (sorry for the tiny images SR uploads)
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    (Original post by Beaneebar)
    So, I was doing a paper (Jan 2011) Newtonian World and I come across this question:

    Q:
    Name:  Screen Shot 2014-04-27 at 15.08.33.png
Views: 156
Size:  17.8 KB
    A:
    Name:  Screen Shot 2014-04-27 at 15.06.34.png
Views: 116
Size:  15.9 KB

    In my answer, I did exactly this only giving the answer as 2.9*10^7 as 6.0*10^24 is only to 2sig.figs./1.d.p..

    Why do I lose a mark for that?

    (sorry for the tiny images SR uploads)
    Where does it say you lose a mark?
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    (Original post by Stonebridge)
    Where does it say you lose a mark?
    Perhaps it's me misreading the mark scheme but doesn't the emboldening of the answer mean that only that answer will be accepted?
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    (Original post by Beaneebar)
    Perhaps it's me misreading the mark scheme but doesn't the emboldening of the answer mean that only that answer will be accepted?
    No. That's just the correct numerical answer for the person marking the paper.
    If you give it correctly to 2 sig figs you're ok.
    In the questions where you are tested on sig figs, the question will tell you this is the case by asking you to express your answer to an appropriate number of sig figs, and the mark scheme will indicate to the marker exactly what is expected and how to award the mark.
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    (Original post by Stonebridge)
    No. That's just the correct numerical answer for the person marking the paper.
    If you give it correctly to 2 sig figs you're ok.
    In the questions where you are tested on sig figs, the question will tell you this is the case by asking you to express your answer to an appropriate number of sig figs, and the mark scheme will indicate to the marker exactly what is expected and how to award the mark.
    Oh, well I guess that clears that up then, thanks.
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    (Original post by Stonebridge)
    No. That's just the correct numerical answer for the person marking the paper.
    If you give it correctly to 2 sig figs you're ok.
    In the questions where you are tested on sig figs, the question will tell you this is the case by asking you to express your answer to an appropriate number of sig figs, and the mark scheme will indicate to the marker exactly what is expected and how to award the mark.
    So say we give an answer to more sig figs than the mark scheme has and it is not featured on the mark scheme, what would you do? Do you do the question yourself and then note a more accurate value to be able to check the other digits?
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    (Original post by ForgottenApple)
    So say we give an answer to more sig figs than the mark scheme has and it is not featured on the mark scheme, what would you do? Do you do the question yourself and then note a more accurate value to be able to check the other digits?
    Ignore the other digits. You can see if it agrees with the mark scheme
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    (Original post by ForgottenApple)
    So say we give an answer to more sig figs than the mark scheme has and it is not featured on the mark scheme, what would you do? Do you do the question yourself and then note a more accurate value to be able to check the other digits?

    Yes - we calculate the answer to more sig figs then check the other digits. When I'm marking exam papers for OCR I write down all the acceptable versions of the answer
    eg 6.0, 5.97, 5.967, 5.9666. etc

    It saves me time when marking 100s of scripts!
 
 
 
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