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Surya Adinata

Propagation of uncertainties?

My chemistry teacher has been teaching us about propagation of error. She thought us that if we sum c=a+b, then Δc=sqrt(Δa^2+Δb^2).(this is according to our Oxford Chemistry Textbook for 2016 syllabus)

 

However, in my physics class, my teacher thought us that if c=a+b, Δc=Δa+Δb. (this is supported by the data booklet.)

 

I've done a research on the internet and found that the former uses standard deviations while the latter uses simpler average errors.

 

So, what should I do with the uncertainties when I sum a and b?

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Use the one provided by the data booklet, If you any definitions or formulas that differ between official IB documents and text books/unofficial documents go for the IB documents without a second thought as it will be more valid according to IB at least.

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As far as I know, the correct formula for the propagation of error is Δc=Δa+Δb. In fact, I have never really seen the other formula that you gave. So I recommend you to go with the formula suggested by the data booklet.

 

Plus, i don't really see the connection between standard deviations and propagation of errors at all. I mean standard deviations are often used when you have lots of different values of measurements for a quantity. While propagation of errors only comes in when we operate on values that have uncertainties. Thus, standard deviations and propagation of errors are often used in entirely different contexts.

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