Monday, October 31, 2011

Measurement --- by Ria Park

Measurement
- Every measurements are the best estimate.
- The exact numbers are when we can COUNT

Absolute Uncertainty
- The uncertainty forms in the unit ofmeasurement, not in a ratio.
- There are two method : 1. - Make at least 3 measurement
                                           - Calculate the average
                                           - The absolute uncertainty is the larrgest difference between the average and the
                                              the lowest or highest measurement.

E.g. Trial #                 Mass of an object
           1                             23.56cm
           2                             23.57cm
           3                             23.34cm    <----- it should be removed.
           4                             23.54cm

 }Average is = (23.56 + 23.57 + 23.34 + 23.54) / 4 = 23.50=
 }Difference between the average and the lowest measurement = 23.54 - 23.50 = 0.04
 }Difference between the average and the highest measurement = 23.57 - 23.50 = 0.07
 }So the mass would be 23.50 ± 0.07cm


- Method 2. - Determine the uncertainty of each intrument
       +) Measure to the best precision as possible when making a measurement. So you should estimate to a fraction 0.1of the smallest segment on the intrument.

E.g. Ruler = 0.1   0.01   0.01
       Themometer = 1℃   0.1℃  0.1℃e
       100㎖ graduated cycilnder = 1㎖   0.1㎖   0.1㎖
       400㎖ beaker = 50㎖   5㎖   5㎖


Relative Uncertain and Sig. Fig.

Relative uncertainty = Absolute Uncertainty / Estimated measurement

- It cane be a) in percent form(%)
                   b) using sig.fig.
- The numebr of sig fig indicates the relative uncertainty : The largest digit in a measurement in uncertain as it could be one digit higher or one digit lower very easily.
- Sig figs are ALL of the certain digits plus ONE uncertain digit in a measurement.