Uncertainty (Measurements)

• averycasille

averycasille

Gold Member
Hello, guys! (And girls, but.. you know..)
There are several things I do not quite understand, so, can you help me clear my doubts? ^^

1) How do I know when to multiply the value of calculated data when it comes to determining the uncertainty of the data?

2) When do I multiply the percentage of accuracy with given data when determining uncertainty?

I have no idea what you are asking, Perhaps you could give an example of your issue.

Sorry for being unclear!
• The manufacturers of a digital voltmeter give, as its specification, accuracy +-1% with an additional uncertainty of +-10mV. The meter reads 4.072V. How should this reading be recorded, together with its uncertainty?

How should this reading be recorded, together with its uncertainty?

You record the reading as is 4.072 V. The uncertainty should be 1% of that reading + 10 mV.= 0.0407 V + .01 V = .0.0417 V =0.042 V ( rounding )

Ohh. So, when the specific accuracy is given, I should always multiply with the data and add it with the additional uncertainty? Is that it?
Also, regarding the rounding off, that should be based on significant figures/decimal place of the data? O.O

so, regarding the rounding off, that should be based on significant figures/decimal place of the data? O.O[/QUOTE

yes

You record the reading as is 4.072 V. The uncertainty should be 1% of that reading + 10 mV.= 0.0407 V + .01 V = .0.0417 V =0.042 V ( rounding )
0.0407V + 0.010 V = 0.0507V which is 0.051 after rounding to an appropriate precision.

Thanks, peeps! But, significant figure OR decimal place? Sorry for asking a lot [emoji848][emoji23][emoji24]

As a general rule, significant figures are not appropriate in the real world. They are a toy for the classroom. The reporting conventions for your organization should be followed. One recommendation from http://web.mit.edu/fluids-modules/www/exper_techniques/1.Recording.Uncertainty.pdf is:

"As described above, to determine a quantity x, we make a measurement, report our best estimate, and report the range over which we are reasonably confidant the actual value lies: (measured value of x) = xbest ± δx ."

e.g. 4.072 ± .051 V

jk494
Thanks for the assistance, everyone. Means a lot [emoji120] Really appreciate it!