AQA AS uncertainty in measurements Watch

honoris
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Report Thread starter 7 years ago
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A question the nelson thornes text book pg.186

Following measurements taken: 425mm,407mm,396mm,415mm,402mm

mean = 409mm

Calculate uncertainty? the answer is 12mm but I do not know how to get to this value.

I thought uncertainty was range/but this gives a value of 14.5mm
Or perhaps add the range of each value from the mean and divideby 5 but this is also incorrect.

How do I do it?
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Stonebridge
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Report 7 years ago
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It's quite possible they wanted you to find the standard deviation, rather than the mean value of the 5 uncertainties (which comes to about 9mm)

This is done by finding the squares of the 5 uncertainties and adding them together.
Then divide by 4 (which is one less than the number of readings)
Then finding the square root of that.
I get 11.3mm which would round to 11mm
It's the nearest I can get to their value.
See this for some background
http://www.rit.edu/cos/uphysics/unce....html#estimate
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honoris
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Report Thread starter 7 years ago
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I know standard deviation but I don't think it's required in physics, perhaps it's a printing error
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Stonebridge
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(Original post by honoris)
I know standard deviation but I don't think it's required in physics, perhaps it's a printing error
Quite possibly.
In practical work you would not need to use standard deviation.
The simple mean uncertainty would be fine.
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