Limitation of physical measurements

Readings vs Measurements

Readings: Only one judgment is made to obtain a value (e.g. using a thermometer, digital voltmeter, measuring cylinder)

Measurements: Requires two judgments (using a ruler, protractor, stopwatch)

Random error definition

Cause unpredictable fluctuations in measurements about the mean, directly affecting the precision of measurements. Common causes include electronic noise, human reaction time, and parallax errors.

How to reduce random errors

1. Taking multiple repeats and calculating a mean
2. Using a computer and data logger to remove the effects of reaction times and to allow more readings taken at smaller intervals
3. Using instruments with a higher resolution to reduce random rounding error

Systematic error definition

Affect every reading in a consistent matter, affecting the accuracy of your measurements, and are caused by equipment and experimental method issues

How to reduce systematic errors

1. Zeroing equipment to avoid any offset errors
2. Checking and calibrating your equipment by measuring a known and trusted value
3. (Radioactivity) Measuring the background count rate without the source and taking away background count rate from final results
4. Using the equipment correctly

Accuracy definition

An accurate measurement is one that is close to the accepted ‘true value’

Resolution definition

The smallest increment an instrument can detect and display

Precision definition

The degree of exactness, affected by the extent of the random errors associated with a measurement. Reflected by the number of significant figures to which a quantity can be reliably measured.

Repeatability definition

Results are repeatable if the original experimenter repeats the experiment and gets the same results

Reproducibility definition

The results are reproducible if the experiment is redone by a different person or with a different technique and the same results are found