Making and Recording Measurements

MAKING AND RECORDING MEASUREMENTS

Reasons for uncertainty in Measurements

1.      The limitations inherent in the measuring instrument.

2.      The conditions under which the measurement was made.

3.      The different ways under which the person uses or reads the measuring instrument.

Terminologies:

1. Fundamental or base unit – the standard unit for length, mass and time.
2. Derived unit a combination of any of the three fundamental base units; i. e.  m/s, m/s²,  ft², m³ etc.
3. Accuracy – refers to the closeness of a measurement to the standard value for a specific physical quantity. It is express either as an absolute error or relative error.
4. Absolute error ( E_A ) is the actual difference between the observed ( O ) or measured value and the accepted value ( A ).

                                                      E_A = | O – A |

5. Relative error ( E_R ) I expressed as a percentage error and is often called a percentage error.

                                                      E_R = E_A/A

6. Absolute deviation ( DA ) is the difference between a single measured value ( O ) and the average         ( M ) of several measurements made in the same way.

                                                      DA = | O – M |

7. Relative deviation ( D_R ) is the percentage average deviation of a set of measurements.

                                                      D_R = D_A/M

8. Precision is the agreement among several measurements tat have made in the same way. It tells how much reproducible the measurements are and is express in terms of the deviation.
9. Tolerance is the degree of precision obtainable in a measuring instrument.
10. Significant figure are those digits in a number that are known with certainty plus the digit that is uncertain.