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# Physics Uncertainties watch

1. A student has a diffraction grating that is marked 3.5 × 103 lines per m.

Calculate the percentage uncertainty in the number of lines per metre suggestedby this marking.

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I'm not really sure how to do this question
2. I'm pretty sure the absolute uncertainty is the lowers unit, so in this case 0.1 X 10^3. From there you can work out the percentage.

I think this being a new spec there is still some confusion about what to estimate the uncertainty as, Different text books are saying different things, but it appears to be the lowest unit from what my class has seen.
3. (Original post by CoreyRobertson)
I'm pretty sure the absolute uncertainty is the lowers unit, so in this case 0.1 X 10^3. From there you can work out the percentage.

I think this being a new spec there is still some confusion about what to estimate the uncertainty as, Different text books are saying different things, but it appears to be the lowest unit from what my class has seen.
I don't quite get what you mean by the lowest unit.
The method I was taught was a significant figures method so for this question, since it's 2sf, I would have thought the uncertainty would be 0.05 x10^3 - this answer isnt right but if I round the answer then it is right. I don't known if this is the correct method but I've noticed on the aqa books mentioning to round uncertainties to make sure it isn't more precise. Idk if that's the method that you're essentially using or not
4. Thats what you would use in the practical assessment but for some reason it's different in the exam.I think the idea is if you use a ruler you take to readings, so 2(0.05 X 10 ^3) which is 0.1 X 10^3. Although, this wouldn't really make sense with a diffraction grating, so I imagine they probably want you to use 1 of the lowest significant figure(not unit sorry).
I imagine the mark scheme will probably be more forgiving in the real thing though.

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