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.
