Combining uncertainties

  • Thread starter swain1
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  • #1
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Homework Statement


If the uncertainty in a measurement of dameter is +-0.02cm is the uncertainty in radius the same or half of this value. The formula given in wikipedia implies that it would be half of the value.

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Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
nrqed
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Homework Statement


If the uncertainty in a measurement of dameter is +-0.02cm is the uncertainty in radius the same or half of this value. The formula given in wikipedia implies that it would be half of the value.

Cheers


Homework Equations





The Attempt at a Solution


Yes, it will be half of this value. If the uncertainty had been given in percent form, then the percent uncertainty on the radius and on the diameter would be the same.
 
  • #3
you should had this formula in your relevant equations thingy:
radius = diameter /2

2 is a number, and has uncertainty of 0
so, use division rule
 
  • #4
30
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Ok thanks guys.
I now have to work out the uncertainty in the voume of a sphere using the radius I have. Any clues on how to get the uncertainty in this value? I would expect that it would be bigger but I can't really understand why?
 
  • #5
30
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I have this formula

deltav/v=3xdeltar/r

Is this correct?
 

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