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    My specifications say that I need to be able to :

    - assess the uncertainty in a derived quantity by simple addition of actual,fractional or percentage uncertainties ( a rigorous statistical treatment is not required ).:confused:


    Can anyone tell me how to do it. We have vacations till August and I have no teacher at hand.


    I also have a question for this:

    The power loss
    P in a resistor is calculated using the formula P = V 2/R.( thats (v square) / R)

    The uncertainty in the potential difference
    V is 3% and the uncertainty in the resistance R is 2%.

    What is the uncertainty in
    P?

    A-
    4% B- 7% C- 8% D- 11%


    So can someone please help me with this. I need to know how to calculate uncertainities.


    Thanks !



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    dealing with the example will show the process nicely

    if the there is a 3% max error in V then the max error in V^2 will be 9%

    this will produce a max error in P of 9% also

    an error of 2% in R could also result in a 2% error in P

    in the extreme case the errors combined could produce an error in P of 11%, which is the answer to the question.

    notice this is simply the "addition ... of percentage uncertainties".
    • Thread Starter
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    (Original post by Drummy)
    dealing with the example will show the process nicely

    if the there is a 3% max error in V then the max error in V^2 will be 9%

    this will produce a max error in P of 9% also

    an error of 2% in R could also result in a 2% error in P

    in the extreme case the errors combined could produce an error in P of 11%, which is the answer to the question.

    notice this is simply the "addition ... of percentage uncertainties".

    But the answer is 8% in the marking scheme.

    So I am confused. :confused:
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    The error in V^2 is 2 X 3% = 6% not 9%

    You multiply the error by the power.
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    Teachercool is correct (I am not worthy!)

    0.97 x 0.97 = 0.9409 which is just 6% out, not 9%, so the answer is 8%
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    If the error for C is x%, then the error for Cn is nx%
    • Thread Starter
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    thanks
 
 
 

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