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Questions about error treatment

  1. Aug 26, 2005 #1
    1.Which of the following experimental techniques reduces the systematic error of the quantity being investigated?

    A.timing a large number of oscillations to find a period

    B.measuring the diameter of a wire repeatedly and calculating the average

    C.adjusting an ammeter to remove its zero error before measuring a current

    D.using a metre rule graduated in 0.5 mm rather than 1 mm to measure diameter



    2.In an experiment to determine the period of oscillation,T, of an oscillation, the time ,t

    ,taken. It is found that the time for 20 complete oscillations is 36.5 +/- 0.2 s.Which of the following sattements is/are correct?

    A.The reading error in t can be reduced by counting 100 oscillations.

    B.The percent error in T is the same as that in t.

    C.The period T determined should be quoted as 1.83 +/- 0.01 s.
     
  2. jcsd
  3. Aug 27, 2005 #2
    I am very confused by the above questions, can anybody tell and explain me the answers? Thanks a lot!
     
  4. Aug 27, 2005 #3
    In question 1, the answer the book provided is C, but I think is A.
    Timing error by using timer is the human reaction time, that is 0.2 seconds, when measure more oscillations, the total time recorded becomes higher , the 0.2 seconds error become more negligible so the percentage of error will be reduced, is that right.
    In question 2, I think the correct answer should include A, but the answer the book provided is B and C only. The reason is the same as question 1.
     
  5. Aug 27, 2005 #4

    lightgrav

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    Homework Helper

    Freedom:
    1)
    If you're trying to do a good job at pendulum timing, you'll either *anticipate*
    the swing by watching beforehand (thereby eliminating the reaction time), or
    you'll NOT anticipate the start NOR the stop, so the reaction time subtracts out
    (the stopwatch runs for the correct duration, just "offset" by a reaction time).
    True, these 2 reaction times might not be identical, but that's RANDOM error.
    A *systematic* error might be a watch that runs fast (more oscillations won't help).
    Another systematic error would be anticipating the "stop" swing but not the "start" swing (which would be a reaction-time error, reduced to T / # counts as you say)
    Removing ammeter's "zero-offset" is definitely removing one systematic error;
    of course its spring could be weak so all the readings are high by some factor.

    In Q2, they didn't tell you whether this .2s uncertainty was a zero-offset type
    or a rate calibration-type. Since the 1880's timer errors have been dominated
    by zero-offset uncertainties (maybe its fast hand shows 10ths of a second!)
    Yes, the zero-offset uncertainties can be reduced by counting more oscillations.

    So, I don't think you're confused by the questions -
    you're exasperated (rightly) by their impractical (but definitionally correct) answers.
     
  6. Aug 28, 2005 #5
    Thank you very much for your explanation, lightgrav
     
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