Uncertainities Flashcards
What is our uncertainty when using an instrument?
The resolution of the instrument (the smallest possible measurement)
What is the uncertainty in a spread of reading?
Range
———
2
How do we calculate % uncertainties?
Estimated uncertainity
———————————- x 100
Mean value
Which uncertainties are always added - absolute or % uncertainties?
% uncertainties
What’s the % uncertainties when multiplying and/or dividing quantities?
Add the % uncertainties of the different quantities
What’s the % uncertainty when multiplying by a constant?
Unchanged
What’s the % uncertainty when a quantity is raised to a power?
Multiplied by the same power
To how many significant figures is uncertainty always quoted to?
1
How do we know which value has contributed most to an uncertainty?
Highest percentage uncertainty
What is there never any uncertainty in?
Numbers or constants
How many significant figures are used for % certainties?
No more than 2 significant figures
How many significant figures have to be used for solute uncertainties every time?
1
What do you have to do once you’ve changes the significant figure of the absolute uncertainty to be 1?
You then have to change the final answer to be in the same number of decimal places
When are zeros significant? Give an example
Any zeros shown on an ammeter for example that trail after a non-zero digit are significant
What is the absolute uncertainty if you’re taking a single reading?
The resolution of the instrument
Resolution of an instrument
The smallest digit
When is the absolute uncertainty the resolution of the instrument?
If you’re taking a single reading
When could you argue that the absolute uncertainty is double?
If it’s something that you have to line up with zero at the start (e.g: measuring the length of something with a ruler)
What could you argue if you’re measuring something where you have to line it up with zero at the start (e. - measuring the length of something with a ruler)
Twice the absolute uncertainty
What would you need to do if you are using double the absolute uncertainty since you’re measuring with something where you have to physically line the equipment up with zero? Give an example
Make it clear that this is exactly how you got the absolute uncertainty
e.g - absolute uncertainty with a ruler +-0.1cm, or +-0.2cm (+-0.1cm each end)
What do we need to do to uncertainties if we have indices?
Multiply up
What do we do in terms of uncertainties if a value is square rooted?
Halve the value