jf1994
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Hi, does anyone know the standard number of significant figures we round to in all questions except the one where it tells you what to round it to?

Thanks
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lerjj
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I think three, unless the figures you are using differ substantially from that. If they do, you'd use the lowest number of s.f. as in any of your primary data.
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1322961
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I'm afraid there is no standard. I've gone through easily over 100 past papers published by AQA from GCSE up to my second year of A-Levels right now and if there's one thing I've learnt you're at the mercy of the mark scheme. This is from doing Maths and Physics (Applied Physics as optional module, so a lot of calculations in that one alone).

I've learned some trends though, most of the time you round to the same number of SF as the values your given in the question.

However for questions carrying on involving your answer to a previous question like 1. a) i) to ii) it varies a lot. For questions where i) is a 'Show that this is x=1.2' question you should round to 2 more significant figures than the answer they give (x=1.189), so that in the next question ii) when you have to use the same value of 'x' you use the answer you calculated and not x=1.2.

There are times where you have to make a judgement call. Like in Simpson's Rule in maths to find the area under a graph I always round 3 SF and have another answer next to it in brackets showing 5 SF. Or when working in units of MeV I always round to a whole number, showing another answer next to it to more SF.
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jf1994
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(Original post by JC 042)
I'm afraid there is no standard. I've gone through easily over 100 past papers published by AQA from GCSE up to my second year of A-Levels right now and if there's one thing I've learnt you're at the mercy of the mark scheme. This is from doing Maths and Physics (Applied Physics as optional module, so a lot of calculations in that one alone).

I've learned some trends though, most of the time you round to the same number of SF as the values your given in the question.

However for questions carrying on involving your answer to a previous question like 1. a) i) to ii) it varies a lot. For questions where i) is a 'Show that this is x=1.2' question you should round to 2 more significant figures than the answer they give (x=1.189), so that in the next question ii) when you have to use the same value of 'x' you use the answer you calculated and not x=1.2.

There are times where you have to make a judgement call. Like in Simpson's Rule in maths to find the area under a graph I always round 3 SF and have another answer next to it in brackets showing 5 SF. Or when working in units of MeV I always round to a whole number, showing another answer next to it to more SF.
Well that's irritating...haha, thanks man.

One more question, in specific charge calculations, should I treat the proton and the neutron as the same mass 1.67 or should I use 1.673 for the proton and 1.675 for the neutron? Thanks!
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1322961
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(Original post by jf1994)
Well that's irritating...haha, thanks man.

One more question, in specific charge calculations, should I treat the proton and the neutron as the same mass 1.67 or should I use 1.673 for the proton and 1.675 for the neutron? Thanks!
When you are calculating mass defect ALWAYS use 1.673x10^-27 and 1.675x10^-27 also include the mass of the electrons emitted 9.11x10^-31.

And don't make the same mistake I did when doing a past paper and think that neutrinos have mass :/
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7jdrabble
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(Original post by JC 042)
I'm afraid there is no standard. I've gone through easily over 100 past papers published by AQA from GCSE up to my second year of A-Levels right now and if there's one thing I've learnt you're at the mercy of the mark scheme. This is from doing Maths and Physics (Applied Physics as optional module, so a lot of calculations in that one alone).I've learned some trends though, most of the time you round to the same number of SF as the values your given in the question. However for questions carrying on involving your answer to a previous question like 1. a) i) to ii) it varies a lot. For questions where i) is a 'Show that this is x=1.2' question you should round to 2 more significant figures than the answer they give (x=1.189), so that in the next question ii) when you have to use the same value of 'x' you use the answer you calculated and not x=1.2.There are times where you have to make a judgement call. Like in Simpson's Rule in maths to find the area under a graph I always round 3 SF and have another answer next to it in brackets showing 5 SF. Or when working in units of MeV I always round to a whole number, showing another answer next to it to more SF.
Hi, I was going to create a new thread asking this but you seem to be the person to ask!I am doing OCR physics AS, I was given a question in a paper in which i had to work out the weight of a a spaceship when given the mass.The mass given was, 1.9 x 10^6 kgObviously i multiplied this by 9.81 to get the answer i wrote down of 1.9 x 10^7 N. In the mark scheme, it said on the far right it said ' Allow a bald answer of 1.9 x 10^7 N, but not if 10 ms-2 seen. On the left, the answer they were looking for was 1.86 x10^7 N.Would i lose the mark for putting 1.9 x 10^7 N?Also (this may be whats causing my confusion) - is 1.9 x 10^6 classes as two significant figures or is it something else? If you can offer any help it would be greatly appreciated! Many thanks!
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Joanne__
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I have the same problem as you. What I usually go by is the number of s.f. used in the question and if that varies the minimum as they are more lenient for less s.f. than more.

I hope that helped!
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Stonebridge
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(Original post by 7jdrabble)
Hi, I was going to create a new thread asking this but you seem to be the person to ask!I am doing OCR physics AS, I was given a question in a paper in which i had to work out the weight of a a spaceship when given the mass.The mass given was, 1.9 x 10^6 kgObviously i multiplied this by 9.81 to get the answer i wrote down of 1.9 x 10^7 N. In the mark scheme, it said on the far right it said ' Allow a bald answer of 1.9 x 10^7 N, but not if 10 ms-2 seen. On the left, the answer they were looking for was 1.86 x10^7 N.Would i lose the mark for putting 1.9 x 10^7 N?Also (this may be whats causing my confusion) - is 1.9 x 10^6 classes as two significant figures or is it something else? If you can offer any help it would be greatly appreciated! Many thanks!
The figure "on the left" is not "the answer they were looking for".
The mark scheme is a note to the examiner, not the model answer.
You 2 sig fig answer is perfectly acceptable. So is a 3 sig fig answer. That is actually what the mark scheme is saying.
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7jdrabble
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(Original post by Stonebridge)
The figure "on the left" is not "the answer they were looking for".
The mark scheme is a note to the examiner, not the model answer.
You 2 sig fig answer is perfectly acceptable. So is a 3 sig fig answer. That is actually what the mark scheme is saying.
Ah right that makes perfect sense! I did my answer was correct but I had to make sure, thanks for your help!
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1322961
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(Original post by 7jdrabble;47673060-)
is 1.9 x 10^6 classes as two significant figures or is it something else? If you can offer any help it would be greatly appreciated! Many thanks!
Yes, 1.9 is 2sf. The answer in the mark scheme was 1.86 is 3sf. I would guess that they expected you to use 3sf as in your calculations you used the acceleration due to gravity at the earths surface 9.81 which is 3sf

Also there's the times when you have stuff starting with zero followed by decimal places. In which case 0.00000005 would be considered 1sf.
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Stonebridge
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(Original post by JC 042)
Yes, 1.9 is 2sf. The answer in the mark scheme was 1.86 is 3sf. I would guess that they expected you to use 3sf as in your calculations you used the acceleration due to gravity at the earths surface 9.81 which is 3sf

Also there's the times when you have stuff starting with zero followed by decimal places. In which case 0.00000005 would be considered 1sf.
No they are not "expecting you to use 3 sig figs." That's not what the mark scheme is saying. Please read my earlier post.
Unless it is obvious from the question (eg atomic masses to 5 or 6 sig figs or a question that specifically asks you to use an appropriate number of sig figs) you can use two or 3. In this question you have used data of 2 sig figs for the mass of the space ship, so you are perfectly entitled to give your final answer to 2 sig figs.
Remember, it isn't an issue unless the question specifically asks for you to use an "appropriate" number of sig figs.
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