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Uncertainities help

Hi, when combing uncertainties in the percentage form, how do you turn them into absolute uncertainty of an experiment. For example after combining percentage error of two values (current and voltage), how would you turn the combined percentage error into absolute error.

I know Percentage uncertainty = (Absolute/measured value)*100

For different units (A and V), what would the measured value be. Would the current and voltage values be added together??
Original post by Tobeadoc
Hi, when combing uncertainties in the percentage form, how do you turn them into absolute uncertainty of an experiment. For example after combining percentage error of two values (current and voltage), how would you turn the combined percentage error into absolute error.

I know Percentage uncertainty = (Absolute/measured value)*100

For different units (A and V), what would the measured value be. Would the current and voltage values be added together??


If, as you say, % uncertainty = ("absolute uncertainty" / "measured value") x 100

then rearrange the formula to find absolute uncertainty, using the % uncertainty you found by combination.
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Tobeadoc
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Original post by Stonebridge
If, as you say, % uncertainty = ("absolute uncertainty" / "measured value") x 100

then rearrange the formula to find absolute uncertainty, using the % uncertainty you found by combination.

But what should be used as the measured value, addition of both the voltage and current values?? I can manipulate the formula no problem, just unsure what should be used in the measured value bit. Thanks
Original post by Tobeadoc
But what should be used as the measured value, addition of both the voltage and current values?? I can manipulate the formula no problem, just unsure what should be used in the measured value bit. Thanks


Lets say you multiply 2 quantities together each with a 5% uncertainty to give 10% altogether.
Your final answer after the multiplication comes to, say, 50.0

The uncertainty in your final value is 10% of 50 which is 0.5
So you say 50.0 ± 0.5

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