accuracyprecisionerror_notes physics.ppt

Precision and error

1. Chapter 3: Measurement:
Accuracy, Precision, and Error

2. Objectives
•Distinguish among accuracy, precision,
and error of a measurement

3. Measurements
•Measurement
–quantity that has both a number and a unit
–fundamental to experimental science so
must be able take and evaluate them

4. Evaluating measurements
•Accuracy
–measure of how close a measurement comes
to the actual or true value of whatever is
measured.
•Precision
–measure of how close a series of
measurements are to one another.

5. Evaluating measurements
•Accuracy vs. Precision

6. Evaluating measurements

7. Evaluating measurements
•Often, we are experimentally determining
a value in the lab that is already known.
–When we do this, we must calculate error in
order to see how accurate and precise our
results are
•In lab reports, you will be required to
determine your error and percent error.

8. Evaluating measurements
•To determine Error:
–The accepted value is the correct value
based on reliable references.
–The experimental value is the value
measured in the lab.
–The difference between the experimental
value and the accepted value is called the
error.
–.

9. Evaluating measurements
•To determine Percent Error:
–The percent error is the absolute value of
the error divided by the accepted value,
multiplied by 100%.
–.

10. Practice: error and percent error
Question 1
•The accepted value for the boiling point
of water is 100.0°C. In the lab, you
experimentally determined it to be
98.7°C. What is the error and percent
error?

11. Practice: error and percent error
Answer 1
•Given
–Accepted value = 100.0°C
–Experimental value = 98.7°C
•Work
–.
–Error = 98.7°C - 100.0°C = -1.3°C
–.

−1.3
o
C
100.0
o
C
×100% = 0.013×100% = 1.3%