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7/23/2019 Assignment 1 - Error Analysis
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Waqar Azeem
NUST-SNS
Error Analysis
Waqar Azeem
NUST-SNS
September 21, 2014
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7/23/2019 Assignment 1 - Error Analysis
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Waqar Azeem
NUST-SNS
Introduction
Some numerical statements are exact: Mary has 3 brothers,
and 2 + 2 = 4. However, all measurements have some de-gree of uncertainty that may come from a variety of sources.The process of evaluating this uncertainty associated witha measurement result is often called uncertainty analysis orerror analysis.
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7/23/2019 Assignment 1 - Error Analysis
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Waqar Azeem
NUST-SNS
Difference Between Accuracy and Precision
Accuracy is the closeness of agreement between a measuredvalue and a true or accepted value. Measurement error is
the amount of inaccuracy.Precision is a measure of how well a result can be deter-mined (without reference to a theoretical or true value). Itis the degree of consistency and agreement among indepen-dent measurements of the same quantity; also the reliabilityor reproducibility of the result.
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Waqar Azeem
NUST-SNS
Difference Between Accuracy and Precision
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7/23/2019 Assignment 1 - Error Analysis
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Waqar Azeem
NUST-SNS
Relative Uncertainty and Relative Error
Precision is often reported quantitatively by using relativeor fractional uncertainty
RelativeUncertainty = uncertainty measuredquantity
(1)
Accuracy is often reported quantitatively by using relativeerror
RelativeError = measured value − expected value expected value
(2)
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7/23/2019 Assignment 1 - Error Analysis
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Waqar Azeem
NUST-SNS
Measuring the Length and Width of a Table
Length (cm) Width (cm)140 93
140.2 93.1
140.1 92.8139.8 92.8139.9 92.9140 93.1
140.1 92.9
139.6 93.2139.5 92.7
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7/23/2019 Assignment 1 - Error Analysis
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Waqar Azeem
NUST-SNS For single measurement:
Length = 140 ± 0.2 (3)
Width = 93 ± 0.2 (4)
Mean Length = 139.9 cm
Mean Width= 92.9 cm
Standard Deviation (S L) = 0.026 cm
Standard Deviation (S W ) = 0.17 cm
Error in Each Measurement = Measurement ± SD
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7/23/2019 Assignment 1 - Error Analysis
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Waqar Azeem
NUST-SNS
Histogram and Normal Distribution
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7/23/2019 Assignment 1 - Error Analysis
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Waqar Azeem
NUST-SNS
Error in Mean
Standard Error (σ) = S √ N
σL = 0.0087 cm
σW = 0.057 cm
Area of Table = 12996.71 cm2
Perimeter of Table = 465.6 cm
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7/23/2019 Assignment 1 - Error Analysis
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Waqar Azeem
NUST-SNS
Propagation of Error
σf =
∂ f
∂ x
2
σ2x +
∂ f
∂ y
2
σ2y (5)
σP = 2
(σ2l + σ2
w ) (6)
σA = lw
σl
l
2
+
σw
w
2
(7)
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7/23/2019 Assignment 1 - Error Analysis
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Waqar Azeem
NUST-SNS
Perimeter of Table = 465.6±
0.307 cm
Area of Table = 12996.71 ± 11.12 cm2
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