How can I calculate uncertainty in my lab report data?

[Hayool]

Hi,

I'm doing a lab report and for every number we need to calculate the uncertainty. I tried to calculate by using the SQRT of the number but i didn't get the same answer as my partner had?
could you help me!

These are the numbers and the uncertainty of my partner which i could not figure out how it was done!

 

[RUber]

It appears the uncertainty was calculated as
$\sqrt{2CPM}$.

 

[Hayool]

It appears the uncertainty was calculated as

Thanks RUber for the fast reply.

Are there any other way to calculate the uncertainty ?
And how can i know I'm using that right way?

 

[RUber]

Normally, the uncertainty comes from your measurement tool, or from the process itself.
Without more information about the expected relationships between your data, I am not sure why you would choose one method over another for uncertainty estimation.

In this document (http://instructor.physics.lsa.umich.edu/int-labs/Statistics.pdf) there is a reference to the "square root rule," which generally says if you know nothing else about a number (large integer), the standard deviation is the square root of the number.

Assuming CPM is a measure of some C per minute, then it might make sense that your count for 2 minutes was 2*CPM.
Then the uncertainty in that measurement would be (using square root rule) $\sqrt{2 CPM}$.