The Four Types of Uncertainties:
There are a total of only four ways that you can obtain
a quantity in lab. It might help you to see this laid out:
| |
You can obtain a quantity by… |
for which the uncertainty is given by… |
| 1) |
… obtaining one or two measurements, |
… estimation. |
| 2) |
… calculation from other numbers using a theoretically based
formula, |
… propagation of uncertainty rules. |
| 3) |
… averaging many values which ideally should be the same (e.g.,
measurements), |
… calculating the standard deviation. |
| 4) |
… obtaining parameters from a least-squares fit of a graph, |
… the output of LINEST(). |
Sometimes methods 3 or 4 can free you from having to do methods 1 or 2.
That is…
- … if you can obtain a bunch of values that you expect to
be the same, then you can skip estimation or propagation of uncertainty and use standard
deviation instead.
- … if you can obtain a bunch of values, use them to make
a graph, and then get parameters from a fit, then you can skip estimation or propagation
of uncertainty and use LINEST() instead.
On the other hand, when you are being extremely careful uncertainties from methods 1 or 2 can be used as part of the process for methods 3 or 4. That level of care is not expected in almost all Geneseo course work.
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