Error, Accuracy, Deviation, and Precision in Lab data.

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Error, Accuracy, Deviation, and Precision in Lab data

Common misconception:  Any mistake in a lab is considered Error?  NOT TRUE, lab Error does NOT include calculating wrong, measuring wrong, etc…

TYPES OF ERRORS: Systematic & Random  Systematic Error u Produces an error that is always the same. Either always high or always low.

TYPES OF SYSTEMATIC ERROR  INSTRUMENTAL ERROR u caused by faulty inaccurate equipment, use in labs  PERSONAL ERROR u caused by some peculiarity or bias of the observer—not acceptable in labs, these are “mistakes”  EXTERNAL ERROR u caused by external conditions, use in labs if applicable

TYPES OF ERRORS  RANDOM ERROR:  Errors that are due solely to chance. They will produce errors that are both above and below the accepted value.  Random errors cannot be corrected but can be minimized by doing a large number of observations  Random error always is present

ACCURACY  The closeness of a measurement to the accepted value for a specific physical quantity

ACCURACY is represented MATHEMATICALLY as ERROR (Relative) or % Difference Accepted Value Mean Experimental Value Absolute Error Absolute Error Relative Error Accepted Value

Percent Difference ( %Diff)  When comparing two values or sets of Data to determine error between them, the calculation is called percent difference First calculate the average if using sets of data

PRECISION  The agreement of several measures that have been made in the same way with each other  It is also how exact an instrument can measure

PRECISION is represented MATHEMATICALLY as DEVIATION (Relative) Mean Experimental Value Each Observed Experimental Value Absolute Deviation done for each measurement Average Absolute Deviation Relative Deviation Mean Experimental Value

Example: Deviation and Error

Absolute and Relative Error First: CALCULATE THE AVERAGE 8.93m/sec 9.36m/sec 10.48m/sec 9.15m/sec 9.33m/sec 47.25m/sec

ABSOLUTE ERROR RELATIVE ERROR

Absolute and Relative Deviation Absolute Deviations

Absolute and Relative Deviation AVERAGE ABSOLUTE DEVIATION D A 0.52 m/s 0.09 m/s 1.03 m/s 0.30 m/s 0.12 m/s 2.06 m/s

Relative Deviation

Explain the difference between: Accuracy and Precision AkaError and Deviation You should be able to: In a lab, be able to calculate Error % or % Difference and Deviation % when needed.