Error Analysis: Addition of Quantities with Uncertainty

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Homework Help Overview

The discussion revolves around error analysis in the context of adding quantities with associated uncertainties. The original poster presents a scenario involving two quantities, u and v, each with specific values and uncertainties, and seeks clarification on whether to use rounded or raw data for calculations.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster questions the appropriate method for combining values with uncertainties, specifically whether to use rounded values or raw data. Some participants provide insights into the significance of figures, while others seek clarification on the origin of the values used.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of how to handle uncertainties in calculations. Some guidance on significant figures has been offered, but the original poster remains uncertain about the application of this information to their specific scenario.

Contextual Notes

The original poster indicates that the values discussed are fabricated for the purpose of a report, which may influence the context of the uncertainty analysis.

NachoNovo
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Hi there,

I have a pretty basic question on error analysis. say we want to obtain a quantity which is given by u+v.

if u = 8.5452545 and has uncert 0.025454. it would be quoted as 8.55(2) and if v = 3.865898 and has uncert 0.04124343.

it would be quoted as 3.87(4).

but when calculating say u+v...

do i a) use 8.55 and 3.87 and their rounded uncertainties.

or b) use the raw data?

thanks for any help.
 
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The uncertainty of a given value must be in the last significant figure.
So if u is given as 8.5452545 the uncertainty is in the last figure 0f 5.
It means that u lies between 8.5452544 and u = 8.5452546.
This is what is meant by SIGNIFICANT figures.
Hope this helps
 
no sorry it doesn't help.

I'm not sure when calculating a new value experimentally if I use the rounded values or the raw values of the old data?

I know what sig figs mean.
 
where did these figures come from?
Are they from a question you have seen?
Were they given to you to test your understanding?
Are they values you have measured?
 
The values are made up. I am writing up a report and wasn't sure what to do.
 

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