Measurements & Uncertainty

Textbook page 560

Systematic Errors

Systematic Errors

Measurement errors in which the measurements differ from the true values by a consistent amount each time a measurement is made.

Random errors

Measurement errors in which measurements vary unpredictably and can happen when any measurement is being made.

Zero Error

The reading is not zero on a measuring device when the quantity being measured is zero (the device is faulty). This is a type of systematic error.

2 potential reasons for random errors

• factors that are not controlled in the experiment

• difficulty in deciding on the reading given by a measuring device.

2 potential reasons for systematic errors

• the way in which measurements are taken

• faulty measuring devices.

True Value

The value that would be obtained in an ideal measurement.

Measurement Error

The difference between a measured value and the true value for the quantity being measured.

Precision

How close repeated measurements are to each other - the closer they are to each other, the more ____ the measurement is.

Accuracy

How close a measurement result is to the true value - the closer it is, the more ____ it is.

Uncertainty in a measurement

The interval within which the true value can be expected to lie.

Absolute uncertainty in the mean of a measurement

Approximated as half the range. This is often expressed as ± value.

Percentage uncertainty in the mean of a measurement

calculated from its absolute uncertainty and mean value as follows: ____ = (absolute uncertainty) / (mean value) × 100

Absolute uncertainty

Uncertainty in a measurement expressed as a numerical value.

Percentage Uncertainty

Uncertainty of a measurement expressed as a percentage of the recorded value.